Ideally, bring temperatures to the lower end of this range on overcast days, and raise them to the upper end (or even slightly higher) during clear, sunny days. You’ll also need to keep humidity below 90% to prevent excessive leaf mold. Ventilate regularly to bring fresh, dry air into the greenhouse, especially on cool, cloudy mornings.

Tomatoes marketed as greenhouse varieties are more tolerant of greenhouse conditions. The letters VFNT and A after the name mean the variety is resistant to disease. [3] X Research source “Indeterminate” tomatoes grow and produce fruit indefinitely, taking advantage of the longer growing season inside a greenhouse. If you’re short on space, plant a “determinate” variety, which stops at a certain height.

Perlite bags or rock wool slabs are the cheapest options in many areas. [4] X Research source Some growers prefer a 1:1 mix of sphagnum peat moss and vermiculite. [5] X Research source Purchase sterile soil mix or make your own. Never use soil or compost from your garden without sterilizing. Choose this option if you do not want to install an irrigation system.

Tomatoes are also easy to grow in a hydroponics system. See this article for detailed instructions.

If you use soil, make sure it is sterile. If you use a soil-less mix, you’ll also need a seedling nutrient solution (see below).

Plant about 10-15% more seeds than you plan on growing, so you can discard the least healthy seedlings.

A 5:2:5 nutrient solution that contains calcium and magnesium is ideal. Dilute the solution according to label instructions.

To keep temperatures under control, you may want to start the tray in partial sun. Move to full sun once all seedlings have sprouted. [11] X Research source This usually takes 5 to 12 days.

If you see any insects, mold, or disease spots on a plant, do not bring any of them to the greenhouse. Give each plant about 4 square feet (0. 37 m2) of floor space. [15] X Research source Planting too close together can reduce airflow and encourage disease.

If your pH is fine, mix in gypsum or calcium sulfate instead to add calcium without changing the pH. [18] X Research source Alternatively, just choose a fertilizer that contains calcium and apply every week or two. In a hydroponics setup, you can supply calcium by injecting calcium nitrate into the irrigation feed. This requires a second injector, as calcium nitrate cannot be stored with your main fertilizer. [19] X Research source

Reduce fertilizer as the final fruits ripen. Do not fertilize in late autumn or winter, unless using artificial grow lights and reliable heaters. [21] X Research source

If the top of your plant is damaged, the top sucker can become the new main stem.

In peak growing season, the plant will grow up to 6 in (15 cm) per week and will need tying each week. Commercial operations save on materials by stringing a wire over each row, with a support post every 20 ft (6m). Wrap the twine around each plant and fasten to the overhead wire. [23] X Trustworthy Source EDIS Electronic database of the University of Florida Institute of Food and Agricultural Sciences’s peer-reviewed articles Go to source For smaller home gardens, you can place a tomato cage over each plant when it is small. These don’t require as much maintenance as staking.

For best results, buy an electric plant vibrator. Touch the vibrator against each flower stalk every other day, at any time between 10am and 2pm. (An electric toothbrush is another, less effective option. ) Alternatively, you can place fans in the greenhouse and direct the airflow over your plants to distribute the pollen. Large operations should consider keeping their own bees. Hand out cotton swabs to your children or family members and have them rub the cotton swabs in the flowers to distribute pollen.

Once fruit starts to grow, thin each cluster down to four or five fruits, removing the smallest or most misshapen. Very large fruits or winter conditions may require going down to three per cluster. Varieties with small fruits may not need any thinning. [25] X Trustworthy Source EDIS Electronic database of the University of Florida Institute of Food and Agricultural Sciences’s peer-reviewed articles Go to source As the fruit matures, snap off older leaves from the lower clusters. This helps improve air circulation. [26] X Research source