If you're an avid gardener with a green thumb, you've probably entertained the thought of greenhouse gardening. Successful amateur gardeners in hardiness zones that do not support year-round gardening often turn to greenhouse gardening to support their habit.
You already know the basics of gardening if you're contemplating a greenhouse. Your goal is to emulate natural growing conditions as closely as possible to maintain a year-round growing season for your plants. The challenge is how to emulate those natural growing conditions.
The selection of a proper greenhouse, its construction and major systems such as heating and cooling play a paramount role in achieving success with greenhouse gardening. All of these factors create the environment in which your plants will thrive or decline. Even if you already have a greenhouse, you may find tips and tricks below that you can incorporate into your existing greenhouse to create better growing conditions.
While all of this may sound complicated and expensive, there are many hobby greenhouse kits available from Home Depot, Wal-Mart, and specialty greenhouse mail order and Internet centers. If you're handy around the house, the "some assembly required" route might work for you. You should be able to assemble a smaller greenhouse or a lean-to greenhouse in several hours. The smaller the greenhouse, the fewer major systems you'll need to install. Small hobby greenhouses in a moderate zone may not require more than a mister, a few lights, and a few passive solar heating drums.
Selecting Your Greenhouse Site
Even before considering what type of greenhouse to purchase, consider your property's sun exposure.
• How much sunlight is available in your back yard?
• Do you have a suitable location with enough natural sunlight to support a greenhouse with minimal supplemental lighting?
• Where is the best available sunlight, year-round?
Locate your greenhouse in the area with the best natural sunlight, if possible. Proper placement can reduce the amount of insulation, lighting and heating necessary to maintain optimal growing conditions and save money.
Other things to consider when selecting your location:
• The site should offer good drainage.
• The site should be level.
• A site close to the driveway provides a convenient drop-off location for plants and supplies.
Buying a Greenhouse
Your next consideration is what type of greenhouse to purchase. You'll find greenhouse frames in wood, plastic or metal. Redwood is the best wood for greenhouses. Because of its rot-resistant quality, redwood frames have a lengthy lifespan. Most pre-fabricated greenhouses come with a metal frame, usually aluminum. Plastic frames are the least expensive.
Other important considerations when purchasing your greenhouse--considerations that directly affect the quality of your growing conditions and your plants--include:
• Glazing
• Foundation
• Heating and Cooling
• Lighting
• Ventilation
• Humidity
Glazing
You can choose from several coverings or glazings. The glazing determines the amount and quality of light that enters the greenhouse. All-glass, including tempered glass, provides a crystal-clear edifice when clean and works best in moderate zones. Glass glazings endure well against the elements, and except for the occasional break, outlast the synthetic glazings, which are susceptible to damage from the elements.
Polycarbonate is a popular glazing. Cost-effective and lightweight, it provides superior insulation. Polycarbonate glazings are available in several weights: single, double, and triple walls. Each additional wall provides an added degree of insulation. Select only as much insulation as required for your zone. Too much insulation will trap more heat than you need, and you'll spend more money than necessary on cooling and shading in warm weather.
Other glazings include polyethylene, fiber-reinforced polyester, polyvinyl chloride, acrylic and fiberglass. Contact your state's Cooperative Extension Service for recommendations and assistance in choosing the greenhouse glazing best suited to your region.
Foundation
Foundations soak up heat during the day and release it at night. Small, low-end greenhouses require no foundation. Higher-end hobby greenhouses often sit atop concrete slabs, resin, brick or treated wood foundations. Concrete slabs require built-in drainage and often require installation by a contractor. Wood is the most popular foundation for smaller greenhouses, and not as expensive as concrete. You'll need to consider the size of your greenhouse and your climate when determining whether you need a foundation.
Some gardeners sink their greenhouse into the soil a few feet. This provides insulation, and steadies the greenhouse. You can cover the soil with a floor of sturdy boards or foam.
Ventilation
Look for a greenhouse that provides natural cross-ventilation. Even hobby greenhouses have removable or extendable roof panels as well as doors and side panels, which facilitate air movement. Hot air escapes through the open roof panels while fresh cooler air flows in through the side panels and doors. A well-ventilated greenhouse exchanges the oxygen produced by plants for carbon dioxide, exchanges hot and cool air and humid and dry air. Good air circulation also minimizes humidity when it's hot.
Heating and Cooling
Greenhouses, by definition, utilize some degree of passive solar heat during the day. Depending on your weather conditions, and assuming that you have adequate insulation, you may require no further heat. If you live in the colder zones, you'll need supplemental heat at night.
Passive and active solar heating provide the most natural heat for your greenhouse. Passive heating traps the heat during the day and releases it at night, using materials such as rocks and water-filled drums to collect the heat. It's also the least expensive and most environmentally friendly way to heat your greenhouse. Active solar heating systems add forced distribution by utilizing electricity and heat pumps to distribute the collected heat at night.
If you periodically need more heat than your heating system produces, place a few milk containers or soda containers full of water throughout the greenhouse. Cut off the top few inches of the containers to provide more open space to collect the heat, and paint the outside of the containers black to retain the heat.
Other popular methods for heating a home greenhouse include electric and gas heating systems. The key to efficient heating is insulation and capturing as much sunlight as possible during the day. Regardless of the primary heating method you choose, utilizing passive solar heating reduces your electricity and gas bills significantly.
Lowering your greenhouse into the ground by a couple of feet provides natural insulation and cuts your heating bills.
If you utilize your greenhouse year-round, you'll need to cool the greenhouse during the mid-day heat in the summer. Turn off lighting to reduce the temperature quickly. Open vents for cross-ventilation, turn on the mister, and use a shade cloth to protect plants from heat and extreme sunlight.
Lighting
Plants require light for photosynthesis whether they grow outside or in the greenhouse. Quality full-spectrum fluorescent lighting is ideal for the greenhouse. High quality bulbs last between two to five years and provide illumination that closely matches the sun's rays. By using the highest-quality fluorescent bulbs, you eliminate many of the problems associated with store-brand bulbs, such as diminished lighting over time, and you'll save money with the increased life span of each bulb.
The reverse side of the lighting coin is the question of shade. Young plants and seedlings require protection from direct sunlight. Use a shading cloth when the sun provides too much light and heat.
Humidity
The ideal humidity for optimal growing conditions is 50 percent to 70 percent. Maintaining a suitable humidity level reduces the amount of time you'll spend watering your plants. The best way to provide constant humidity is with a mister, which supplies a continuous fine (almost invisible) mist to the plants. As the air evaporates, the air temperature cools, so the mister doubles as a cooling system in warmer weather. The fine misters work in most climates except for the most hot and arid climates. Water misters, which are similar to fine misters, except that their spray is heavier, work well in arid climates.
Maintenance
To maintain the glazing and keep bacteria and mold at bay, wash the interior panels, shelves and benches twice yearly with a simple solution of soap and water, and rinse thoroughly. Wash down or rinse the outside of the panels when necessary, usually no more often than twice yearly. Clean panels allow the best sunlight into the greenhouse. Schedule one cleaning just before you bring the plants in for the winter. You'll have more room to move around the greenhouse. Schedule the other cleaning just after you've moved the plants outdoors.
Miscellaneous Greenhouse Growing Tips
• Water all greenhouse plants at the soil level. It's humid in the greenhouse, and watering the leaves invites black rot, mold and fungus.
• When you transplant the seedling into a larger container, place a stake in the new pot. That way, when it's time to tie the plant, you don't have to look around for a stake.
• To increase space in your greenhouse, add shelves and benches. You can use the benches to hold potting trays with seedlings. Seal the wood to prevent rot. You'll probably have to replace the benches after a few years' use. Be sure that you have proper drainage to carry off the excess water from the plants on the benches.
• While it's tempting to keep your plants nice and warm, a cool environment makes the plants hardier. You don't want to take your plants from a hot greenhouse into the cool spring air before you've hardened them, so ease back on the temperature a bit before moving the plants outdoors in the spring.
• While water is essential to your plants growth, a convenient water source is essential to your well-being. Install a water facet in or near the greenhouse so that you don't have to lug gallons of water into the greenhouse.
• Dormant plants require less water and heat. Water dormant greenhouse plants only when the soil is dry.
• Water seedlings in the early morning or late afternoon. Mid-day watering can burn the delicate plants.
• You can recycle the water that collects in your greenhouse drain and use it for watering.
Most of the tips you have just read are common sense, but conditions in a greenhouse do not mimic the outdoor garden. Use the tips as a checklist, and pay attention to your plants closely. They'll let you know when the greenhouse conditions need adjusting.
