Gardeners have grown tomatoes in hothouses for almost 100 years, according to the University of Kentucky Extension. Hothouses, also called heated greenhouses, provide ideal conditions for growing tomatoes all year. During cool winter months, use a hothouse's heater to keep your tomatoes growing strong. Use the protective benefits of a greenhouse along with other gardening techniques that help grow healthy tomato plants.
Fill a five-gallon pot half full, if using transplants, with a potting mix with additives such as compost and peat moss. If using seeds, start in peat pots and keep in an area that maintains consistent temperatures of 75 to 80 degrees Fahrenheit. Transplant after seeds emerge and develop five to seven true leaves.
Set the transplant in the middle on top of the soil and pour more soil around the sides and up to the plant's base. Pack soil firmly around the roots and the plant's base.
Push a cage in the soil around the edge of the pot until it feels secure.
Water the soil each day until moist. Test the wetness of the soil by placing a fingertip in the soil. If it feels moist, skip watering until the next day.
Turn up the hothouse heater first thing in the morning to a temperature between 75 and 85 degrees Fahrenheit. At sunset, turn the temperature down to 60 to 70 degrees Fahrenheit.
Apply a fertilizer formulated for tomatoes by following the application instructions provided. The University of Kentucky Extension recommends using a fertilizer "moderate in nitrogen and high in phosphorus, potassium, calcium and magnesium."