Planting the Tomato Plant. 1  1. Choose a sunny spot. Place tomato plants in full sun. 2  2. Space the plants 18 to 36 inches (45 to 90 cm) apart. This is usually enough space to allow you to get in between the plants to water, weed, and harvest. 3  3. Transplant the plant deeply. Bury about 50 to 80 percent of the plant.