Heirloom is an old time variety of tomatoes that your great-grandparents may have grown; the hybrid tomato was introduced in the United States in 1940. The hybrid variety is now the most common variety found in grocery stores, but if you are looking for a brilliantly colored, richly flavored tomato that is quite different in taste and texture from store-bought tomatoes, the heirloom is the one to grow. Heirloom plants tend to produce less fruit than the hybrid variety, so be sure to grow a few extra plants, using several different varieties to ensure a continuous harvest.
Wait until the last frost has passed and there is no chance of more cold weather before preparing your garden soil for planting. Till the soil at least one foot deep and work in organic compost to make the soil well-draining. Heirloom tomatoes do not thrive in heavy, water-logged soils.
Dig a hole for each plant that is twice as big as the root ball for each plant, spacing the holes about 36 inches apart with rows at least 40 to 48 inches apart. Heirloom tomatoes can grow to 6 feet high and need plenty of room to grow and allow good air circulation between plants, which helps prevent diseases.
Add a handful of organic plant food in each hole and then add tomato plants. Backfill halfway with soil, water thoroughly and, after water has drained out, finish filling with soil and tamp down gently with your hands to firm over.
Water your plants well after planting and keep watered deeply each week. Use a soaker hose for the deepest watering that gets clear down to the roots. Run for one hour once a week and only water if the soil seems dry. It's normal for heirloom tomatoes to droop some in really hot weather so that is not the best indicator of watering needs.
Add a 4- to 5-inch layer of mulch such as straw, pine needles, hay or dry leaves. Mulching is extremely important for Heirloom tomatoes because it helps hold moisture in the soil, keep weeds and grass from taking over the plants and reduces pests. Keep 1-2 inches around the main stem of the plant free of mulch.
Support your tomato plants to prevent them from falling over as they get taller, which can cause the plants to break. Ordinary stakes will not be strong enough to support these plants, since heirloom tomatoes can grow up to 6 feet tall; using a trellis or old ladder placed between plants can both work well.
Feed your heirloom tomatoes with a high nitrogen organic liquid fish fertilizer at the time of planting and for the first month which will help to develop a good root system and healthy foliage. After the first month, apply an organic liquid fertilizer low in nitrogen and high in potassium and phosphate which will encourage blossoms and fruit set increasing the amount of tomatoes produced in a season.