Growing your own vegetables is a fun, profitable and delicious hobby, but in many regions the growing season is too short to get a really good yield. Raising greenhouse vegetables is a great way to extend your growing season and give yourself and your family months of fresh, delicious produce every growing season.
Select a good site for your greenhouse. Sunlight is the most important factor. Your greenhouse should be in a spot that gets good light both in the summer, when the sun is overhead at midday, and during the winter, when it doesn't rise as high. If you can, select a site that has flat ground as well, and a good location. Having your greenhouse near, or even connected to your house will make it much more convenient.
Regulate the temperature inside your greenhouse. For most vegetables, you want to keep the daytime temperature around 80 degrees F, and you want the nighttime temperature to be as warm as possible. A good way to regulate the temperature is by storing full jugs of water painted black in the greenhouse. They will absorb heat during the day and release it at night, keeping the temperature stable. You might also have to open doors or vents in the greenhouse during the day to keep it from overheating.
Plant your vegetables in the correct months. You can usually start greenhouse vegetables a few months earlier than you can outdoor ones. In many climates, you can start onions, carrots, radishes and other bulbs in January, lettuce, celery, eggplant and peppers in March and so on. If you live very far north, you might have to wait until later in the year. Talk to a horticulturist at your local garden store about when to plant greenhouse vegetables where you live.
Start your vegetables according to the instructions on the seed packages. For most vegetables, you will need to start the seeds in flats with a mix of 1 part compost, 1 part garden soil and 1 part sand. You might want to stagger your plantings of each type of vegetable over several weeks or even a couple months so that you will have a long harvest of ripe vegetables instead of a whole bunch ripening all at once.
Once your plants have germinated, transplant them. You can put them in planters or grow them in the ground if you have good soil in the floor of your greenhouse. Plant them in the same soil and with the same spacing as you would if you were growing your vegetables outside.
Keep your soil damp but not wet. The air in a greenhouse is usually more damp than the outside air, so your plants will require less water. You can add gravel to the bottom of your plant beds or poke small holes in the planters to increase drainage.