A greenhouse is a good way to grow vegetables even when the weather is too cold for tender vegetables to naturally grow. Greenhouses work by trapping solar radiation inside layers of clear material such as glass or plastic. The more layers of glass or plastic between the inside of a greenhouse and the outside world, the warmer the greenhouse. This means you can grow cold-hardy vegetables year-round and start tender vegetables well before the last average frost date for your region.
Space your plants properly so that there is adequate circulation between the plants. If you use raised beds, thin out weak and spindly plants as they grow. If you grow plants in containers, set each container far enough apart that air can pass freely between the plants. This will help deter sickness and diseases. You may wish to include a fan in the greenhouse to stir the air. Small and low-growing plants such as lettuce or radishes need less space between them than vines or tall plants such as cucumber or tomato.
Water the soil as it dries out. Most vegetables prefer soil that is the consistency of a wrung-out sponge. Examine each plant for signs of disease or pest infestation. Bacterial or fungal diseases can enter a greenhouse through contaminated soil or on plants or seeds.
Remove plants from a greenhouse that show signs of disease. Manage pests with traps, insecticidal soap, and natural repellents such as basil, marigold or garlic plants. Hand-pick pests off the plants or release beneficial insects such as ladybugs into your greenhouse.
Pollinate vegetable blossoms to ensure that the plants produce vegetables. Tomatoes and peppers are self-fruitful. To pollinate them, tap on the plant to release pollen. Pollinate cucumbers, melon or squash by transferring pollen from male blossoms to the flowers of female blossoms with a paintbrush.
Add mulch around the bottoms of plants to help reduce evaporation and reduce the frequency of watering.