GROWING FROM THE GREENHOUSE

A Quick Greenhouse Guide for the Organic Gardener

By

Nicole Wrinn

© 2014 Nicole Wrinn

West Jaro Publishing

All rights reserved. This book or any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of the publisher except for the use of brief quotations in a book review.

Although the author and publisher have made every effort to ensure that the information in this book was correct at press time, the author and publisher do not assume and hereby disclaim any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from negligence, accident, or any other cause.

Your Sanctuary Awaits!

With increasing concerns about toxic pesticides and inefficient agricultural methods used on commercial farms, not to mention the cost of organically grown produce, many people have turned to organic gardening as a means of taking back some control over what goes into their bodies and what comes out of their wallets. By using safe, homemade pesticides, smart irrigation systems, and efficient garden layouts, gardeners are able to simultaneously sustain themselves, save money, and create a better environment for the flora and fauna of their region.

Unfortunately, no matter what precautions you take, your outdoor garden will always be at the mercy of seasonal weather, soil conditions, and pests. Planting drought-resistant vegetation can help, but there is a limited selection of such plants, and as a result you may not be able to plant your favorite vegetables or flowers. On the other hand, what if you have more rain than usual? Too much water can be just as detrimental as too little. Planting itself can be troublesome, as you must take into account sunlight exposure, soil acidity, windbreaks, as well as spacing between plants. It takes time to have your soil professionally tested. Sometimes, in spite of all your efforts, those hungry little insects simply won’t be deterred. In addition, there is tilling to be done, and mulch, compost and/or fertilizer to spread. And whether you live in an apartment building with a rooftop garden or in a suburban neighborhood with a backyard garden, you’ll always have family members or neighbors who want to tell you how to manage your garden.

Have you ever wished you could find some sort of refuge, where you could be the boss, plant whatever you like, and be truly self-sufficient? Well, you can—with a greenhouse! Now, due to the time and expense involved, it’s not an enterprise to be entered into lightly. A greenhouse requires a real investment, but we believe that this investment will pay invaluable dividends in the form of a beautiful green sanctuary that you can call your own.

Also called a conservatory, a greenhouse can be a freestanding element of the landscape, or it can be attached to your house. The underlying principle involves building a structure covered with a material such as glass (traditional), fiberglass, plastic, or polyethylene, which will then act as a selective medium for the sun’s electromagnetic radiation. The covering material absorbs this radiation, heating the plants and soil inside the greenhouse.

Greenhouses enable you to extend the growing season, and control temperature, light, and moisture in order to obtain desired results. You can also use the controlled atmosphere to get acquainted with a variety of plants, or to specialize in one species. This will improve your gardening skills tremendously. A greenhouse will also protect your plants from bad weather, birds, animals, and harmful insects, though you can allow beneficial animals, such as bumblebees, to enter. It’s much easier to deal with pests and diseases in a greenhouse than outside, where there are many variables to rule out. You can also save money on seeds by collecting your own.

As we mentioned, a greenhouse should be a personal sanctuary. If you have disabilities or limited mobility, you can still enjoy gardening with a greenhouse instead of trying to maintain a large outdoor garden. Remember, the greenhouse will be a reflection of you, so you can build and lay it out any way you choose, as small or as large as you wish. You can make everything easy to reach. If you live in an apartment, you can place your greenhouse on the roof, above all the hustle and bustle in the streets below. A greenhouse can be especially inviting for those who have a demanding job and need a place where they can unwind in the presence of nature, be alone with their thoughts, and have some control over the situation. If you have a family, children or grandchildren, you might find that they come to appreciate life more after spending some time helping you in the greenhouse.

We hope that you’ll find building and maintaining a greenhouse worthwhile and fulfilling. In the following pages you’ll read about the different kinds of greenhouses, how to irrigate, vent, and heat them, what tools and materials are required, and how to plant vegetables and flowers in them.

The door is open...let’s step inside. Your sanctuary awaits!

Table of Contents

Your Sanctuary Awaits!

Table of Contents

Chapter 1: Asking the Right Questions

Chapter 2: Decisions, Decisions

Location

Structure

Frame Design

Chapter 3: Building Your Wonderland

First Things First

Basic Components

Blueprint

Foundation

Flooring

Frame Materials

Covering

Roofing

Shelves and Benches

Chapter 4: Putting the “Green” in Greenhouse

Lighting

Carbon Dioxide

Passive Solar Heating

Winter Air Circulation

Summer Ventilation and Air Conditioning

Irrigation

Automation

Chapter 5: Planting Tips

Soil Care

Containers

Raised Bed

Pest Control

Pollination

Other Tips

Chapter 6: Some Like It Hot

Warm Season Fruit and Vegetables

Warm Season Plants and Flowers

Chapter 7: Keepin’ It Cool

Cool Season Fruit and Vegetables

Cool Season Plants and Flowers

Thinking outside the Box

Further Reading

Books

Websites

Other Books by this Author …

One Last Thing…

Chapter 1: Asking the Right Questions

Before we discuss greenhouse options, let’s address some preliminary questions.

s Do you prefer to build or buy?

Of course we encourage you to construct the greenhouse yourself, as this will allow for extensive customization, improve your building skills, provide a project for the whole family, and simply be a lot of fun! However, if you’re not skilled in construction or physically able, you may want to buy a prefabricated greenhouse, such as one from eartheasy. If you don’t have the budget for that, but are willing to try your hand at building, you can use mostly inexpensive, recycled materials.

Important Note: For most greenhouses, you shouldn’t need a building permit, but just to be on the safe side, you should check with local authorities to find out how large a building you can construct without a permit. You would hate to get in trouble if you forget to pull a simple permit.

s What are you going to use the greenhouse for?

1. Cold frames are basically “mini-greenhouses.” In early spring, you set a cold frame directly on a garden bed to help seedlings get established before planting time. The cold frame protects them from frost and cold rain. You can move cold frames around for different plants.

2. Starter (or hobby) greenhouses are small to mid-size greenhouses used to propagate seeds and starter plants before transplanting. You generally have a potting shed nearby (or inside the greenhouse, if large enough) where you can keep your tools, repot plants, and cure harvested crops prior to storage.

3. Grower greenhouses are the largest type, used to grow crops year-round. There is room enough inside for propagating seeds, growing crops, and preparing harvest crops for storage.

Consider both daytime and nighttime temperatures in your region and compare these to the requirements of your desired plants. Also note the average date of the first frost to estimate how long you can extend the growing season. The USDA Plant Hardiness Zone Map is a good place to start.

s What Temperature do you need to provide

After determining what kind of garden you want to have and the temperature requirements of the plants, you need to select the appropriate greenhouse environment. This will influence how you build the greenhouse and what kind of temperature control systems you use.

1. Hot greenhouses have an inside temperature of 65-85°F, ideal for growing tropical and exotic plants. If you live in a cold climate, you’ll have to add supplemental heating and lighting to maintain the required temperature. See Chapter6 for a list of warm season crops, plants, and flowers.

2. Warm greenhouses have an inside temperature of 55-65°F (cooler than the outside air in summer), which allows you to grow a large variety of plants, just like in an outdoor garden.

3. Cool greenhouses have an inside temperature of 45-50°F (warmer than the outside air in winter), and are perfect for starting seedlings to transplant once the growing season begins, or for growing plants that prefer cooler conditions. In this case, you don’t have to use any supplemental methods to maintain the temperature. See Chapter 7 for a list of cool season crops, plants, and flowers.

s How much available space do you have?

Do you want a large or small greenhouse? If space is limited, don’t worry; it’s quite feasible to grow more than 100 plants in an 8x10 ft. greenhouse!

s Will the greenhouse be the main feature of your garden?

Will it be freestanding or attached to your house?

s What kind of weather conditions does your region usually experience?

Heavy rain, drought, strong winds, etc. play a role in determining your needs. Particularly in windy conditions, your greenhouse needs a strong, sturdy frame.

s Animal Protection

Are there birds, deer, rodents, or other animals in the area that could damage unprotected plants? Also, you need to make sure the greenhouse is childproof so that your children, grandchildren, or neighbors’ kids don’t disturb anything or injure themselves somehow. You should always supervise children around the greenhouse.

If you’re still unsure where to begin, you can consult a fellow gardener who has a greenhouse or speak to your local cooperative extension office.

Chapter 2: Decisions, Decisions

If you choose to build your own greenhouse, the number of design options can be both overwhelming and exhilarating. We’ll go through the alternatives one by one, outlining the pros and cons and any unique characteristics of each. Unless otherwise stated, all illustrations are adapted from the University of Maryland Cooperative Extension Service.

Location

Regardless of whether it is attached or freestanding, the greenhouse should be located so that it receives the most sunlight possible. This will maximize solar energy, requiring less artificial heating. Most plants prefer sunlight all day, but as long as they get sufficient sunlight in the morning and shade in the late afternoon, they will thrive. Morning sunlight acts as a kickstarter for photosynthesis, encouraging growth. We recommend situating the greenhouse on the south, southeast, or east side of your home or shade trees. This way plants will be exposed to sunlight in the morning, as well as during the winter months when the sun is low. If you don’t have room on these sides, you can place the greenhouse on the southwest or west side, where the plants will receive sunlight in the afternoon. If possible, avoid locations on the north side of the house, unless you’re growing shade-loving varieties.

You can utilize existing trees to shade the greenhouse, reducing the need for artificial cooling (though ventilation is still necessary). Deciduous trees, such as maple and oak, can block the scorching sun on late summer afternoons, but they shouldn’t be in the way of that vital morning sunlight. Since they shed their leaves in the fall, these trees will also allow sunlight to reach your greenhouse during the winter. Evergreen trees, on the other hand, do not shed their leaves, so they must not deprive the greenhouse of winter sunlight. Instead, use them as a windbreak by placing the greenhouse to the south. When using trees for shade, make sure your greenhouse covering and frame can withstand falling branches! Also, there is always the risk of a whole tree crashing onto the structure, so check that all nearby trees are healthy (dead and diseased trees are usually the first casualties in a storm).

Make sure water will not pool around the foundation of the greenhouse, but will drain away. Avoid marshy or unstable soil.

Position the greenhouse conveniently near to sources of heat, water, electricity, windbreaks, and the home itself. You should be able to access and enter it easily, even with physical disabilities or special equipment such as a wheelchair, power chair, or walker. Consider the slope, the path, the width of the doorway, and the steps, if any. It’s also a good idea to have a workplace (a shed or open area) nearby for potting plants, and a dry, cool place to keep tools.

Structure

Basic considerations include bench space, storage space, and room for expansion. While small greenhouses may be less expensive, you have to contend with the rapid temperature fluctuations. In short, these greenhouses have a large area for heat transfer, but a small volume of air inside; this causes the temperature to change quickly. For easier management, we recommend a minimum size of 6 ft. wide by 12 ft. long for an even-span or freestanding greenhouse (see below).

Lean-to

First up, we have the lean-to, which is the least expensive design due to the fact that the side of your house serves as a ready-made wall. (If your house’s perimeter has an L-shaped portion, you can snuggle the greenhouse right into that corner. Then you’d only need to build two walls and a roof). Most lean-tos are 7-12 feet wide (the wider the structure, the higher the supporting wall must be), with the long, front wall at an angle calculated to transmit the most sunlight to the supporting wall (often painted white). This design provides significant support for the greenhouse, as opposed to a freestanding structure.

You may find that the greenhouse’s proximity to the house will cause “sweating” behind the siding, and in turn, mold. In certain conditions, the humidity can cause condensation inside your home, depending on the type of supporting wall, whether it is cladded, or made of brick or wood. If there is a doorway communicating between the greenhouse and a finished room (even a shed), the interior walls can be damaged. You’ll probably have to reinforce the insulation of the abutting wall to prevent moisture seeping in from the greenhouse. Lacking that other greenhouse wall, lean-tos can be difficult to ventilate. Lastly, don’t place a lean-to under a roof that is prone to heavy snow, ice, or rain runoff, as this could damage the greenhouse.

Even-span

Unlike lean-tos, even-span greenhouses are complete structures attached to a building at only one end, which allows for better ventilation and temperature control. The ideal width is 17-18 feet, and you can install 2-3 benches for vegetables. However, you must balance the larger growing space with the higher expense of this design.

Window-mounted

This is a fairly low-cost option, particularly suitable for apartment dwellers. The greenhouse can be attached to a south- or east-facing window, extending about a foot from the house. It can hold 2-3 shelves.

Freestanding

Lacking the support of an existing building, freestanding greenhouses must be designed to withstand the elements. They also require their own water and energy sources. At the same time, they give you the freedom of location, space, and style. As with an even-span greenhouse, the ideal width is 17-18 feet. You could install a central bench, flanked by two walkways, with two side benches running along the walls.

Frame Design

The following frames apply to even-span or freestanding structures. If you plan to build a lean-to, visualize these frames cut in half and attached to a supporting wall.

1. Quonset

Made of galvanized steel pipe or electrical conduit, the Quonset is a circular frame with a plastic covering. Unfortunately, the low sidewall height restricts movement and storage.

2. Gothic

The Gothic frame has more sidewall space than the Quonset. The arches are usually made of wood and joined at the ridge.

3. Rigid-frame

In contrast to the Quonset and Gothic frames, the rigid-frame has vertical sidewalls and rafters, with no supporting columns or trusses. Plywood gusset plates connect the sidewall supports to the rafters, creating a single rigid frame that allows for maximum interior space and air circulation. However, since the frame is not circular, you need to provide it with a strong foundation to handle the lateral load.

4. Post and rafter

This design requires a good deal of wood or metal. You must build it with strong sidewall posts, embedding them deeply into the foundation so that the structure can withstand pressure from the rafters and wind. If constructed properly, you’ll have adequate sidewall space and good air circulation.

5. A-frame

Similar to the post and rafter design, the A-frame has a collar beam that ties the upper parts of the rafters together. Sidewall space is limited.

Chapter 3: Building Your Wonderland

Now that you have a few style ideas in mind, you need to pick out which materials are appropriate for your budget and the purpose of the greenhouse.

First Things First

We already mentioned that recycled and salvaged materials can significantly lower the cost of your greenhouse. For instance, a prefabricated 8x12 ft. glass greenhouse can cost up to $5,000, while a DIY greenhouse of the same size, using post-consumer windows and doors, will run only $300 or $400. To capitalize on this, you should collect the materials first and construct as much of the greenhouse as possible from these. Then you can fill in around them with new materials. See what you have around the yard or garage. If necessary, look for auctions and garage sales in your area or go to freecycle.org, craiglist.com, or a Habitat Restore. You may be surprised at how exciting the search is—like a treasure hunt!

Basic Components

Let’s review the main structural components of a greenhouse, illustrated by the following diagram from the Texas A&M Agrilife Extension.

Rafters (A) provide the primary vertical support for a greenhouse. They can be trusses (e.g. post and rafter frame) or curved arches (e.g. Gothic frame). Purlins (E) run between the rafters, spaced 4-8 feet apart, and provide horizontal support. They may be connected by a cross tie if high winds warrant extra support. Ranging in height from 1 to 10 feet, side posts (C) give additional vertical support, and the corresponding sidewalls (D) influence production efficiency and ventilation, depending on height and covering. End walls (B) can be made solid for additional support (e.g. Quonset structure).

Blueprint

You don’t have to be an artist to draw up a good blueprint for your greenhouse. After observing potential building sites and making notes, select the best site and simply make a sketch with the desired dimensions clearly marked. This will help you stay on plan.

For a step-by-step guide for building a greenhouse, we recommend that you read an article from Mother Earth News. It has details on the foundation, flooring, frame, and roof. The article specifically concerns a lean-to, but you can adapt these methods to other designs.

For a large number of greenhouse plans, including heating, cooling, and ventilation schemes, please check out Build It Solar. It’s an invaluable source for any first-time greenhouse grower!

Foundation

Apart from the frame, the foundation of your greenhouse is crucial to its strength and efficiency. The last thing you want is an awesome-looking greenhouse that starts leaning or has a cracked foundation. Because of its importance, you might want to have the foundation professionally installed.

If you decide to construct the foundation yourself, it is imperative that you check the local building codes to find out where the frost line is, so you know how deep to set the footings (they should always be deeper than the frost line). Otherwise an inspector may come along and tell you the greenhouse isn’t up to code, or the first frost will crack the foundation anyway. A poorly built foundation will cause you endless trouble. There is no room for guesswork or shortcuts.

First, level the building site, while making sure it slopes enough to drain water away from the greenhouse. Excavation by shovel may take 1-2 days, depending on the size of the site. You can also rent an excavator or hire a construction crew. Next, cover the site with a weed barrier, such as landscape fabric, though a 3-inch layer of wood chips (mulch) will work just as well and often even better. Pour gravel over the site, particularly around the border.

Once the site is prepared, it’s time to construct the foundation, which can take many forms based on your specific needs. Follow the directions on Remodeling.com for forming up and leveling concrete footings. Remember, the footings must be at least 8 inches wide. Before pouring the concrete for the footings, reinforce them with rebar both horizontally and vertically.

Put ¼ or 1/3 inch “D” anchor bolts in the poured concrete. Space them to match the bearing plate and/or vertical posts of the greenhouse. Also space 2-inch drainage holes about 4 feet apart in the footing walls. You may also have to install drainage channels made of tile or gravel. Before creating foundation drains, please consult Green Building Advisor.

Remove the wooden forms after the concrete cures, and then backfill the trenches with gravel and/or dirt.

Flooring

Concrete makes good permanent flooring because it resists stains and moisture. However, pouring and troweling concrete is not most people’s idea of fun. You may prefer to lay bricks in a base layer of sand or mortar. Bricks cost more than concrete, but you can salvage them from a demolished building. On the other hand, you can add temporary flooring made of several inches of gravel, which you can spray with water to create a humid atmosphere. Walkways should be 24-36 inches wide and can be covered with concrete, gravel, or stone. Some gardeners add a rodent barrier (hardware mesh) or a weed barrier (landscape fabric) to the floor.

Frame Materials

1. Aluminum has proven to be the most durable and economical frame material. It is strong, lightweight, and will not rust.

2. Galvanized steel is inexpensive, extremely strong, and long lasting. Its weight makes transportation and assembly difficult, but you’ll be thankful for it during windy conditions.

3. Wood decays quickly in the moist greenhouse environment, though cedar, Redwood, Douglas fir, and cypress are rot-resistant. You can also purchase pressure-treated wood that lasts longer.

4. Plastic resin is less expensive than aluminum and insulates better than steel or aluminum. Unfortunately, plastic frames aren’t very strong, so you should only use them with small greenhouses. Industrial resins also pose environmental risks.

Covering

Greenhouse coverings vary by type and lifespan, but they must be suited for both the frame and the foundation. As a general rule, the covering should let in the amount of light appropriate for the greenhouse’s purpose. If you’ll be germinating seeds and starting transplants, you want warm, direct light, provided by a clear covering, such as glass. If you’ll be growing year-round crops, you want a diffused covering, such as fiberglass or multi-walled polycarbonate, which will facilitate the most efficient photosynthesis. Diffused light reaches the plants from many angles, causing them to develop in a more balanced, compact way instead of competing with each other for a limited light source. If you have an all-purpose greenhouse for both germinating seeds and growing crops full-term, you want a semi-diffused covering, such as polyethylene film. You can even use two different coverings: diffused on the roof and clear on the sides.

The following are common greenhouse coverings. Although widely used, we did not include polyvinyl chloride (PVC) because it poses too many health risks.

1. Glass

This is the traditional covering. It’s inexpensive to build and maintain, and suits practically any style. If you want an aesthetically pleasing, maintenance-free, weather-tight, and energy efficient greenhouse, you should combine a glass covering with an aluminum frame. Aluminum works best because glass requires a strong, well-fitted frame to support its weight and rigidity. When working with glass, you can’t cut corners with the foundation or frame; otherwise the structure won’t hold up.

If you choose glass, you have a prime opportunity to save big on recycled or salvaged windows, storm doors, and patio doors.

The downside to glass is that it breaks easily. Fortunately, we can now use tempered glass, which is 2-3 times stronger than regular glass, is impact-resistant, and can withstand seasonal expansion and contraction. You can use 3mm-thick panes, but 4mm is stronger and will insulate better. During installation, you must protect the edges of the pane so a knock won’t shatter it. Tempered glass does not diffuse light.

2. Fiberglass

Fiberglass can work well as a greenhouse covering, as it is strong, lightweight, and hail-proof, but you must buy a good grade that will last and consistently provide diffused light. Translucent fiberglass, coated with polyvinyl fluoride (PVF) film, has a lifespan of up to 15-20 years. One plus of PVF is that it emits no volatile organic compounds (VOCs) during application.

When the PVF coating wears off after 6-10 years, the fiberglass panels will become discolored and collect dirt. Re-coat the panels or, if necessary, replace them. Do this immediately, or the exposed fiberglass fibers may cause skin, eye, and upper respiratory irritation in humans and animals.

3. Polyethylene film

Polyethylene is the most common plastic. While the fact that it is derived from petroleum and natural gas (both fossil fuels) is disconcerting, the biggest issue is that it does not easily decompose and clogs up landfills.

Polyethylene film is inexpensive and easy to maintain. You can buy utility-grade polyethylene, which will last about a year, at the local hardware store. UV-treated, commercial-grade polyethylene will last 12-18 months. Polyethylene covers steel well because it fastens more easily than other materials. Being translucent, it provides semi-diffused light. In normal outdoor conditions, you may be able to get the film to last 3-5 years, but there is always the risk of stretching, sagging, and tearing due to wind, snow, and falling branches.

4. Twin-walled polyethylene

This grade of polyethylene is flexible, though not as much as regular polyethylene. It comes in rolls or sheets, where the inner walls separate the sheets to create an internal air space. UV-treated, twin-walled polyethylene provides soft, diffused light. About 75% natural light is still able to penetrate.

5. Polycarbonate

Polycarbonate panels come in different thicknesses. They cover plastic frames well and can last over 15 years. While less expensive than tempered glass, polycarbonate is less durable and scratch resistant. It’s also less flexible than twin-walled polyethylene. However, like glass, single-walled polycarbonate does provide clear, undiffused light. Multi-walled polycarbonate panels are stronger and more insulative.

If coated with laminated acrylic sheets, polycarbonate releases volatile organic compounds (VOCs). Also, a lot of energy is required to dispose of polycarbonate (by burning).

6. Twin-walled polycarbonate

As we mentioned, multi-walled polycarbonate panels provide strength and insulation due to internal air spaces. They share this quality with twin-walled polyethylene. You can save up to 30% on energy costs compared to other materials. In addition, multi-walled polycarbonates are UV-treated and provide diffused light (letting in about 80% natural). They usually carry a 10-year warranty for light transmission. Polycarbonates are great for curved greenhouse designs, such as the Quonset.

7. Triple-walled polycarbonate

Triple-walled polycarbonates work well in cold climates, as they can withstand snow and freezing temperatures. They are very strong and retain heat excellently.

Roofing

Don’t use transparent glass or plastic for the entire roof, or the greenhouse will overheat in the summer and freeze during the winter. Most plants need only 30% top light. Instead, concentrate on reinforcing the roof to protect it against precipitation, especially snow.

Remember to make the roof tall enough to accommodate tall shrubs and small trees!

Shelves and Benches

This is another area where you can let your imagination run wild. Consider building a potting shed. Hunt around for an old wooden workbench or table that you can repurpose as a potting bench. If you’re so inclined, you can build your own out of scrap wood. A few wooden cabinets, which you can decorate, wouldn’t hurt either. Aluminum bakery racks make good plant shelves, but really any rack of shelves (e.g. a finished hardwood bookcase) will do. For optimal customization, make the shelves adjustable. If there’s room along any side of the greenhouse, add a few utility shelves or brackets to place tools and equipment out of the way. The main consideration for greenhouse “furniture” is moisture-resistance, because it’s going to be humid in there all the time. You want wood that won’t rot, and plastic that won’t decay quickly. Several preservatives are available for preserving wood against high humidity, but some should not be used in the greenhouse due to their non-green derivation (e.g. paraffin wax) or just plain ineffectiveness (e.g. linseed oil). On the other hand, two component epoxy polyamide paint (sounds bad but actually low VOCs, no lead or chromate) works well, as does polyurethane varnish and natural beeswax (if properly prepared).

Chapter 4: Putting the “Green” in Greenhouse

While a greenhouse will not usually pay for itself except in terms of enjoyable gardening (unless you plan to sell cut flowers or vegetables), you need to make sure that, once it’s built, it won’t cost a lot of money to operate. You can ensure cost-effectiveness by designing an energy- and resource-efficient greenhouse.

Lighting

It’s wise to use artificial lighting sparingly, but if winters in your region are long and dark, or if your greenhouse never receives adequate sun exposure, you can help your plants by installing fluorescent lamps. Some types are specially designed for plants, while others mimic sunlight. You can also use both cool and warm bulbs together. To ensure that each plant receives the correct amount of light, make use of shade panels, screening fabrics, and washable shading paint.

Carbon Dioxide

Plants won’t flourish without an adequate amount of CO₂. While some gardeners purchase equipment to pump CO₂ into their greenhouses, this is often a waste of money. You should monitor CO₂ levels (see section on automation below), and if they do drop below an acceptable amount, you can add the gas the natural way: with animals. Keeping some chickens in a coop connected to the greenhouse can provide CO₂, warmth, and manure without a lot of hassle or expense.

Passive Solar Heating

Obviously, a greenhouse is supposed to use solar radiation (i.e. cost-free energy) to create a heated atmosphere. Ideally, you should be able to rely solely on the sun for heat without resorting to artificial heating (which requires electricity), even in winter. You can achieve passive solar heating through the following properties:

1. Orientation

As mentioned in Chapter 2, the greenhouse should be facing to the south, southeast, or east for maximum sun exposure. Your latitude and climate will determine the proper orientation.

2. Solar Collector

You can engineer the north wall of the greenhouse so that it collects heat. One method is to construct the wall with concrete-filled brick (i.e. thermal mass). Such a wall will absorb 30-35% of the solar radiation. In winter, the greenhouse will reach the desired temperature by mid-morning, at which time you should begin ventilation. In Colorado, the nighttime temperature inside this kind of greenhouse dropped to only 35°F when outside temperatures fell to –17°F. No supplemental heating was required.

Another method is to build the wall with water-filled plastic milk jugs. (A great way to recycle!) These jugs will absorb 90% of the solar radiation, as opposed to the 30-35% for a brick wall. In Colorado, the nighttime temperature inside this kind of greenhouse dropped to only 39°F when outside temperatures fell to -17°F. No supplemental heating was required. The wall should be a bookcase-style frame, with cells no higher than two jugs. The jugs should be returnable, heavyweight jugs, not larger than 2 gallons. Spray-paint the jugs flat black, fill them with water, and add 1 tablespoon of bleach per jug to prevent algae growth. Caulk around the cap of the jug. Heavy-duty jugs will last longer, but they will eventually have to be replaced due to leaks. You can use other types of containers, as long as they don’t hold more than 2 gallons and are durable.

One thing to keep in mind when using the greenhouse itself as a solar collector: you may not always be able to keep the air temperature at plant-growing levels. It really depends on how well the greenhouse is constructed and on the climate of your region. If passive solar heating is insufficient, you can replace or supplement it with a 220-volt circuit electric heater or a small gas or oil wall-heater.

3. Insulation

Construct the greenhouse so as to keep cold air from coming in and heat from going out. The north, east, and west walls should be insulated to an R-value of R38. For instance, you can use recycled double-glazed patio door glass as a covering (reducing heat loss by 25-30%) and night curtains (conserving energy by an additional 30-50%). Some gardeners add bubble wrap to the windows (or inflate their own air pockets using plastic sheets), and others make entire walls out of straw bales, which provide superb insulation.

You should insulate the foundation and floor as well so that the ground below doesn’t rob the structure of heat.

Winter Air Circulation

In winter, you don’t want the hot air to rise towards the roof, leaving your plants cold. Installing a fan to circulate the air can keep the air temperature uniform. Calculate the air volume of your greenhouse and buy an electric fan with a CFM equal to ¼ of that number. Assuming the greenhouse is a small rectangle, place two single-speed fans in opposite corners, diagonally across from each other, so that the air will circulate in an oval pattern. Leave the fans on 24/7 during the winter, but turn them off when summer arrives.

However, increasing electricity (and in turn, fossil fuel) use is not recommended if you want to be environmentally conscious. You can circulate air with solar-powered automatic windows or louvers, or with a well-placed windmill. If you must use a fan, you could power it with a solar panel or a small wind turbine. On the other hand, if you use the greenhouse for cool season crops, you need only open the windows to let in fresh air.

Summer Ventilation and Air Conditioning

In summer, you need proper ventilation to control temperature, restore CO₂ levels, and remove excess moisture. There are two different methods of ventilating the greenhouse.

1. Natural ventilation

This uses ridge-line roof vents with louvers. When warm air rises and escapes, cooler air is drawn in. You can open windows manually (as long as there are screens in place to keep out bugs), but solar-powered louvers open and shut automatically when the temperature reaches a certain level.

2. Mechanical ventilation

Here an exhaust fan removes used air from one end of the greenhouse, while motorized louvers bring in fresh air at the other end. You need to purchase an exhaust fan with a CFM equal to the air volume of the greenhouse.

If ventilation alone doesn’t lower the air temperature enough, consider purchasing a small evaporative cooler, which will produce moist, cool air while heated air escapes through vents in the roof or exhaust fans on the sidewalls. (Build It Solar has several plans for constructing such a cooler). This system will work best when the outside humidity is low (i.e. in arid or drought-prone regions). After removing the water evaporation components, you can use the cooler for ventilation purposes. Calculate the volume of the greenhouse and buy a cooler with a capacity of 1.0-1.5 times that number. Alternately, you can place evaporative pads on the louvers, so that the exhaust fans will pull the cool, moist air through the greenhouse. For added cooling, you can shade the greenhouse with wood or aluminum roll-up screens, or paint.

Irrigation

Over- or under-watering are common problems in the greenhouse setting. You should always water consistently.

Hand-watering is usually not sufficient or healthful for plants. The root zone needs to be watered precisely to reduce water stress. Also, leaves can easily develop problems if they remain wet. That’s why automated drip irrigation is essential for proper plant growth. You can hook up the drip irrigation system to your water line (but the chlorine in the water may cause plants to develop brown tips), or you can harvest rainwater from the greenhouse roof and store it in a tank, to be used when necessary. Then all you have to do is add a drip hose to each raised bed or container. We advise setting up a timer to control the system.

Automation

Automation allows you to go to work each day or take a short vacation without worrying about your plants while you’re gone. The best way to automate the temperature control process is to install a thermostat for each unit or a central controller for all of them. The thermostat or controller should be positioned in a shady spot, away from the sidewalls, where there is constant air flow. As illustrated in this diagram from the University of Maryland Cooperative Extension Service, the device should be housed in an aspirated, white-painted box.

Inside the box, a small fan moves the air across the sensor. If the box is properly shaded and painted, the sensor will provide accurate temperature readings and adjust the environmental systems appropriately. The timer can control lighting, heating, ventilation, and irrigation.

Chapter 5: Planting Tips

Below you’ll find some pointers for planting your vegetables and flowers and creating a healthy environment for them.

Soil Care

Like an outdoor garden, a greenhouse garden needs soil rich in nutrients, which can be provided by fertilizer and compost. However, vegetables can accumulate unhealthy amounts of nitrates, so it’s advisable to use non-nitrogen fertilizers and plant-based (as opposed to manure-based) composts. Regarding compost, add mostly “brown” waste to your bin, i.e. carbon-containing materials, such as fallen leaves, straw, bark, pine needles, soiled paper, sawdust, and woodchips. This means you’ll be adding dry yard waste instead of kitchen scraps and grass clippings. By contrast, most fruit trees need nitrogen-based fertilizer and compost, so in this case you should add “green” waste to your bin.

Some gardeners leave the vegetable soil fallow during the summer, allowing the intense heat to kill pathogens and mollusks, but it will probably be necessary to grow a cover crop (e.g. cowpea) during that time and then till it in in the fall, followed by grain grass (to absorb excess nitrogen).

Also consider adding a vermicomposting bin to the greenhouse, as worm castings make excellent fertilizer.

Never use bark or wood chips as mulch in the growing beds. Weed-free straw works well to retain moisture and moderate temperature.

Containers

For starting seeds and transplants (not fruits or vegetables), use black plastic flats (for displaying plant containers) and individual plastic plant containers, as well as Styrofoam cups and plastic yogurt cups—in fact, anything you can find! Fill containers with gravel, marbles, charcoal, or even cracked walnuts to facilitate drainage. Broken clay pots can also serve this purpose, though they must be soaked in water for a few minutes before use so that the clay won’t suck the moisture out of the potting soil. Whiskey barrels and big pots can accommodate the large vegetation, such as fruit trees.

Raised Bed

In a raised bed (constructed of wood or stone), you can plant vegetables in traditional rows, but we recommend a block style layout, coupled with companion planting, for better efficiency. Both Organic Gardening Magazine and Mother Earth News provide good guides for companion planting. “Companions” can shade other plants, provide support (instead of a stake), and keep away pests. Some vegetables, such as tomatoes, grow fine in their own containers.

Pest Control

Sheltering plants in a greenhouse won’t eliminate pests unless you take a few preventative measures. For instance, you can plant insect-repellent herbs around and/or inside the greenhouse. As a supplement or substitution for this, you can make your own insecticides with natural, organic ingredients. Caution! If you’re growing vegetables, don’t use any homemade remedies that are not safe for food crops, as they can leave a harmful residue. Have major insect problems? Plant a border of marigolds around the greenhouse, as well as inside. They repel practically everything.

Pollination

One of the few downsides to growing plants in a greenhouse is that you have to play the pollinator. David L. Green provides an illustrated guide for gardeners who are new to this practice. For plants that have separate male and female flowers, it’s important to be able to recognize sexes, capture the pollen without injuring the flowers, and transfer it successfully. Q-tips and small, soft paintbrushes work well here. If you plan to grow such plants, such as squash and cucumbers, you should also know the symptoms of inadequate pollination. Green provides a separate guide for hand-pollinating this group of vegetables. For tomatoes and other plants that have both sexual parts in a single flower, you can gently shake the plants or tap the flowers. Tomato vines need shaking once a day to produce good fruit.

For natural pollination, you can buy a package of bumblebees, which are far more efficient than other bees. Being solitary and docile, bumblebees are also well-suited to living in a greenhouse. You can install a hive inside the greenhouse and just let the bees do their thing. You won’t have to worry about inadequate pollination or a bunch of stir-crazy bees!

Other Tips

Always space plants so that they have “room to breathe.”

Coat hangers can be fashioned into trellises for the vining plants.

If planting a bulb, make sure that you pack the soil around it. Leaving air pockets behind can result in plant death.

If plants aren’t growing, try adding some crushed egg shells to the soil. If the soil is too alkaline, add some coffee grounds.

If winter temperatures concern you, select frost-resistant varieties.

Don’t be alarmed when lettuce leaves go limp in winter—this is simply a strategy the plants employ to prevent cellular damage due to freezing. When the temperature rises, the leaves will perk up again.

As gardener Harvey Ussery puts it, the soil in a greenhouse is like a rechargeable battery: it absorbs a tremendous amount of heat during the day, so on cold winter nights it can afford to lose some of that energy without the root zone freezing. In other words, don’t be alarmed by a layer of frost on the growing beds!

If you start winter crops in late summer or early fall, and plant what seems a surplus, you’ll be able to harvest until the days grow longer in late winter and you can plant new crops. In some regions, the greenhouse is too hot in late summer/early fall to start winter crop seeds, so gardeners must grow them indoors under artificial lighting (e.g. grow lights) and then transplant them in the greenhouse when they’re strong enough.

Scrub produce thoroughly before consuming.

Water seeds only lightly for the first few times; otherwise they may not take root properly.

Keep your production area separate from your preparation area. In other words, the potting shed should literally be a shed or another room. This will ensure that the greenhouse is organized and tidy.

Plant vegetation that will produce high yield relative to the space it takes up.

Chapter 6: Some Like It Hot

So-called “warm season” crops, plants, and flowers grow best in a hot or warm greenhouse (60-85°F). They need high light intensity during the day. The temperature can’t drop too low at night (must stay at 55-65°F). If you extend the season into winter, you’ll have to use some kind of solar heat collector. Also, don’t plant warm season plants alongside cool season plants; there’s no way to set the temperature for both to thrive. That’s why in Chapter 1 we asked you to decide whether to go with a hot, warm, or cool greenhouse before purchasing any materials or plants.

The following tables provide some helpful data for growing warm season plants in a greenhouse. Remember, the deeper the container, the more water and nutrients the plant will have. Also, this list is confined to common greenhouse varieties. For instance, beans are not usually grown in greenhouses, so they are omitted here. Note: if you want to grow fruit-bearing trees, buy dwarf varieties (to fit under a normal roof) and space them several feet apart. Pack soil around root balls of trees to eliminate air pockets, which can kill the trees. If planting depths aren’t available in the tables, consult the seed packet.

Warm Season Fruit and Vegetables

Warm Season Plants and Flowers

Chapter 7: Keepin’ It Cool

So-called “cool season” vegetables, plants, and flowers grow best in a cool greenhouse (45-50°F). They prefer daytime temperatures of 50-70°F. The temperature can fall to 35°F at night without harming them. These plants don’t require high intensity light, but you should fertilize them frequently and never allow the soil to become dry. Don’t plant cool season plants alongside warm season plants; there’s no way to set the temperature for both to thrive. That’s why in Chapter 1 we asked you to decide whether to go with a hot, warm, or cool greenhouse before purchasing any materials or plants.

The following tables provide some helpful data for growing cool season plants in a greenhouse. Remember, the deeper the container, the more water and nutrients the plant will have. Also, this list is confined to common greenhouse varieties. For instance, potatoes are not usually grown in greenhouses, so they are omitted here. In addition, carrots and peas should be overwintered outside to free up greenhouse space. If planting depths aren’t available in the tables below, consult the seed packet.

Cool Season Fruit and Vegetables

Cool Season Plants and Flowers

Thinking outside the Box

After reading this book, we hope you’ve come away inspired by the endless possibilities that a greenhouse offers. We can’t emphasize enough that a greenhouse should reflect the gardener’s personality. Structural requirements are merely the canvas on which you can paint your gardening dreams. Not only can you eat fresh salads and fruit and cut beautiful flowers during the bleak days of winter, you can retire to your living laboratory after a hard day’s work in the summer.

Of course, we intended this book to be a true introductory guide, so our list of options is certainly not exhaustive. Feel free to visit any of the links scattered through the preceding pages, and explore those provided in the Further Reading section below. As you probably noticed, there is no single right way to design a greenhouse. Many of the greenhouse “experts” are simply gardeners who have used a lot of trial-and-error methods, failed many times, and finally found success. This kind of gardening necessitates experimentation, because each person’s climate, budget, and preferences are different. While you can learn a great deal from gardeners who have paved the way before you, don’t hesitate to be a pioneer yourself. Think outside the box—er, greenhouse! Never stop asking questions, such as “What unconventional materials could I use?” and “How can I customize the environmental systems or space?” In other words, we want this book to be a starting point, not an end point. Take the ideas we’ve discussed and read more about them elsewhere; make them your own. If you come up with a new idea, try it out!

We’ve said before that a greenhouse should be a sanctuary, for the plants as well as for you. You’re certainly not obligated to share it with anyone else, but we encourage you to do so. Searching for recycled materials can be a husband-and-wife project, while building the structure can involve the whole family. And once the greenhouse is in operation, you can use it to teach the next generation about caring for nature. In this way, a greenhouse can be a priceless legacy.

Further Reading

Books

Coleman, Eliot. The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses. 2009.

Freeman, Mark. Gardening in Your Greenhouse (Greenhouse Basics). 1998.

Marshall, Roger. How to Build Your Own Greenhouse: Designs and Plans to Meet Your Growing Needs. 2006.

Schmidt, Philip. The Complete Guide to Greenhouses & Garden Projects: Greenhouses, Cold Frames, Compost Bins, Trellises, Planting Beds, Potting Benches & More (Black & Decker Complete Guide). 2011.

Smith, Shane. Greenhouse Gardener's Companion, Revised: Growing Food & Flowers in Your Greenhouse or Sunspace. 2000.

Websites

http://www.wvu.edu/~agexten/hortcult/greenhou/building.htm

http://eartheasy.com/how-to-buy-a-greenhouse.html

http://www.motherearthnews.com

http://homeguides.sfgate.com

http://aggie-horticulture.tamu.edu

https://hrt.msu.edu/Energy/Notebook/pdf/Sec4/Solar_and_Wind_Energy_by_AJ_Both.pdf

http://simplifyandsave.weebly.com/1/post/2013/08/straw-bale-greenhouse.html

http://www.homesteadingtoday.com

http://remodeling-projects.com/concrete_footing.htm

http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/how-install-foundation-drain

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#Greenhouse Plans

http://www.toolbase.org/Best-Practices/Failure-Prevention/protecting-wood-from-humidity

http://www.cmg.colostate.edu/gardennotes.shtml

http://garden.lovetoknow.com/wiki/Winter_Gardening_Greenhouse

http://orchidflowers.wordpress.com/2011/08/22/which-flowers-can-be-grown-in-greenhouse/

http://www.gardenguides.com/100472-list-flowers-grow-greenhouse.html

http://forums2.gardenweb.com

http://theselfsufficientliving.com/growing-vegetables-and-fruits-in-a-green-house/

http://www.koppertonline.com/pollination.asp

http://www.thegardenhelper.com

http://www.organicgardening.com/learn-and-grow/

http://tipnut.com/natural-pesticides/

http://www.raintreenursery.com/growingfruitincontainers.html

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One Last Thing…

When you turn the page, Kindle will give you the opportunity to rate the book and share your thoughts on Facebook and Twitter. If you believe the book is worth sharing, would you take a few seconds to let your friends know about it? If it turns out to make a difference in their lives, they’ll be forever grateful to you. As will I.

All the best,

Nicole Wrinn