Greenhouse Planting Guide

Ideal Growing Conditions

• High humidity can cause problems with plants. One way to avert this problem is to space the plants far enough apart that air can easily flow around them. Another option is to install a fan to help circulate both the air and the heat. The use of a fan also can help prevent disease and bring fresh carbon dioxide to the plants' leaves. Maintaining an even temperature in a greenhouse is difficult, so instead of trying to do this, position thermometers throughout the greenhouse, near the floor, at eye level and at the ceiling. Select plants that will thrive in the various temperature ranges once you know what they are. Use soaker hoses or another form of automatic watering to keep plants from drying out, especially during the summer. Finally, install grow lights to supplement the natural light during the winter.

Seasonal Growing

• The temperature range inside a greenhouse will vary according to the season, just like it does outside. During the summer, a greenhouse can get quite hot, especially if there is not enough ventilation. Tropical plants or warm-weather vegetables such as eggplants are good choices for keeping in a greenhouse but do leave doors and windows open, plus use a fan to circulate the air. A variety of flowers and vegetables will thrive in a greenhouse from fall through winter. Select cool season plants for greenhouses that remain on the cool side and warm season plants for heated greenhouses. Stocks, flowering sweet peas, lettuce, cabbage and peas are ideal crops for the cool greenhouse. Tomatoes, melons and a wide array of tropical plants are ideal for warm greenhouses.

Companion Planting

• Companion planting works as well in the greenhouse as it does in the garden. Greenhouses are an ideal place for bugs to overwinter. Plants grown outdoors, then moved indoors for the winter, often bring bugs in with them. Even if you do not see any, there is still a chance there could be bugs or bug eggs hiding in the soil. Purchasing and releasing beneficial insects is one way to combat this problem, but the easier way is simply to grow plants close to one another that help deter insects. Nasturtiums help repel whiteflies, aphids and squash bugs. Marigolds help rid the soil of nematodes and Mexican bean beetles seem to avoid this plant. Both of these annual flowers, which are flowers that grow, flower, set seed and die in one season, will thrive in the greenhouse.

Pollination

• Greenhouse-grown fruits and vegetables will require pollination to produce, just as flowers will require pollination to set seed. You can leave this to chance, or you can formulate a plan of action. During warm weather when the greenhouse is open, pollinators will find their way inside, but during the winter there is a good chance there are not enough pollinators left to do the job. Releasing beneficial insects, such as honeybees or butterflies, into the greenhouse is one option, however be aware they may leave if there is not a source of insects and natural nectar to sustain them. Another option is to hand pollinate, which is labor intensive but well worth the extra effort.