Tips for the beginning greenhouse gardener
The benefit of having a greenhouse is that you can extend your growing season and grow vegetables and flowers all year long. The first decision you must make that will guide all of your other decisions is what do you want to grow? It is important to be realistic and consider your level of experience and the time that you have available for gardening. Having and maintaining a greenhouse is much like having a pet that requires daily attention.
What do you want to grow? Do you want to grow cool season or warm season vegetables? Do you want to use the greenhouse for seed starting or plant propagation? Or grow specialty plants such as orchids or bromeliads? The temperature requirements, as well as lighting needs, will be based on what you want to grow.
In general, an unheated greenhouse will allow you to grow plants that are rated for 1 Climate Zone warmer than yours or about 5-8 degrees Fahrenheit. This can add 2 to 3 weeks on each end of the growing season. If you intend to provide supplemental heat and light, you can grow any plant you desire at the cost of electricity or gas.
Greenhouses are typically divided into four types based on the plant’s temperature requirements:
• The cool (unheated) greenhouse (also known as a high tunnel),
•The temperate greenhouse (40-50 degrees),
• The warm greenhouse (55-60 degrees), and
• The tropical greenhouse (60-70 degrees).
Once you have decided what you want to grow, it is necessary to create the proper environment. If you have chosen to heat the greenhouse, you will need to research the methods of heating. Typically for a beginner with a small greenhouse, electric heat is recommended due to the ease of use, but it can become costly. Other methods include propane, oil, natural gas, wood, radiant heaters, and inground water heaters. These require a greater initial investment and consideration of proper ventilation to the outside to prevent the buildup of carbon monoxide and ethylene gas.
During the summer it may be difficult to maintain a consistent temperature. Since the greenhouse is designed to trap and maintain heat, cooling one down can be difficult. A couple of options include shade cloth and evaporative air coolers. It is necessary that you monitor the temperature in the greenhouse. You can accomplish this with a thermometer and a journal to log the temperatures. You can also invest in a monitoring device.
Ventilation for the greenhouse varies with the season. During the summer, use an exhaust ventilation fan along with roof or wall vents. This will allow cooler air in and hot air out. During the winter an oscillating fan can be used for air circulation to maintain a uniform temperature and to keep leaf surfaces dry.
During late spring and summer, your greenhouse should get enough natural lighting. If you want to grow in the fall and winter, supplemental lighting will be required for strong, healthy plants. LED grow lights and high output fluorescent lamp strips are popular because they output full spectrum light, are energy efficient and can cover larger areas. If you have a small green house, a normal fluorescent strip hung 3-7 inches above the plants will do.
One mistake that beginners make is overstocking the greenhouse. Young plants need less space than they will need when they get just a few weeks older. The number of plants that you can grow depends on the space needed when they reach maturity. Overcrowding can lead to stressed plants that are more susceptible to disease and insect damage. Start conservatively; you can add more plants later. Also it is best for the beginner to limit the diversity of the plants.
The first and best pest management strategy is to keep pests out of the greenhouse from the beginning. Installing insect screening on air intakes will reduce the likelihood of insects and mites getting into the greenhouse. Outside plants and shrubs should be kept away from the greenhouse since they can harbor unwanted pests. If you have an outside garden, the greenhouse
work should always be done before going into the garden. If you intend to move outdoor plants into the greenhouse, be sure to check for pests and spray beforehand. Starting with seeds in the greenhouse is preferable to using cutting or seedlings obtained from somewhere else. This process makes it less likely to introduce insects, mites, or disease.
There is a lot of information available to support the hobby greenhouse grower. You might want to consider joining a gardening club or joining the Hobby Greenhouse Association. You can
obtain information online at www.hobbygreenhouse.org or the Virginia Cooperative Extension at https://ext.vt.edu.
Lori Deprisco is a Master Gardener with the Virginia Cooperative Extension Prince George County Office. Virginia Master Gardeners are volunteer educators who work within their communities to encourage and promote environmentally sound horticulture practices through sustainable landscape management education and training. Virginia Master Gardeners bring the resources of Virginia’s land-universities, Virginia Tech and Virginia State University to the people of the commonwealth.