By growing tomatoes in a hothouse, you can extend the growing season and get maximum yields for your plants. In southern states, plant hothouse tomatoes in the summer and harvest from fall through spring. In northern states, plant hothouse tomatoes in the winter to harvest spring through fall.
Fill starter trays with moistened potting mix. Plant two to three tomato seeds per tray cell. Sprinkle a thin layer of potting mix--no more than 1/4 inch deep--on top to cover the seeds. Drizzle with water.
Keep the soil moist until the tomato plants germinate, which usually takes seven to ten days. Thin seedlings to one per cell after the tomato plants have developed their first true leaves. Allow seedlings to grow for four to five weeks, watering them whenever the soil becomes dry.
Put a thin layer of gravel on the bottom of a large container for transplanting. Add moistened potting mix until it is about 2/3 full and center a seedling in the container. Fill in around the plant with potting mix, covering most of the stem up until the bottom leaves. Repeat until you have all of the seedlings in large containers. Water the tomato plants.
Water tomato plants daily or as needed with about 2 qt. of water per plant.
Apply a premixed 5-10-10 fertilizer according to manufacturer's directions. To decrease chances of over-fertilization, the North Carolina University Extension recommends applying half the recommended fertilizer twice as often.
Maintain the hothouse temperature between 60 to 90 degrees Fahrenheit, the range at which tomatoes set fruit. Use a shade cloth if needed to prevent the hothouse from getting too hot, and a heater to keep the plants adequately warm during winter growing.
Consider supplemental lighting for tomato plants growing in a hothouse during winter months. If possible, ensure tomato plants receive 12 to 14 hours of light per day.
Set tomato cages around the plants as they reach a height of about 10 inches. The cages help conserve space as they encourage vines to grow upward and also eliminate the need to prune. Tuck any stray vines back into the cage, as needed.