For the serious gardener or culinary chef, greenhouse tomatoes provide a beneficial way to have rich, juicy produce high in vitamins A and C and lycopene year-round. This way you do not have to be concerned with regional climate or bad soil. The key to raising tomatoes in a greenhouse is to prepare the soil properly and ensure the tomatoes receive sufficient light, either from the sun or artificial lights.
Mix the potting soil with 10 to 15 percent worm castings for the seedling trays and add 1 tsp. of lime per gallon of soil. This helps prevent future blossom end rot. Fill the seedling trays with the prepared soil. Make sure the seedling trays have proper drainage.
Lightly push two or three tomato seeds into each seedling tray pocket about 1/3 inch deep. Moisten the soil with the water bottle. Continue to spritz the seed tray a couple times per day for the next two weeks to keep the seeds moist. The ideal temperature for tomato seed germination is 80 degrees F.
Keep 12 hours of light on the seedlings each day, either sun or grow lights.
Fill the second largest planters, the 6-inch ones, with the prepared soil. Use your fingers to create shallow holes about 2 inches deep and transplant the seedlings from the seedling tray when they are 2 to 3 inches tall.
Change the temperature. At this point, the young tomato plants need the atmosphere to be about 75 degrees F. during the daytime and about 65 degrees F. in the evening. Continue to keep 12 hours of light on the plants.
Continue to water the tomato plants so the soil is regularly moist. Do not let it dry out. On average, this means you should water about every two to three days. Fertilize the plants with a 16-16-16 fertilizer.
Fill the third largest planter pot, the 1-gallon container, with the prepared soil. Transplant the tomato plants once they are 12 inches tall to this container for maturation by carefully scooping them up with a trowel.
Observe the tomato plants over the next two months, continuing to keep the soil moist and provide 12 hours of sunlight. By the end of two months, the plants should start to flower, with fruiting in another eight weeks.
Harvest the fruit when it is a rich, red color (or if they are different variety like yellow or green) and heavy on the vine with firm skin.