When growing heirloom tomatoes, it’s important to start the seeds indoors about six to eight weeks before the last frost date in a sterilized seed-starting medium. A fluorescent grow light on a timer placed no more than 6 inches (15 cm) from the heirloom tomato plant will ensure that the seedlings get 12 to 14 hours of light each day. Once the tomatoes have produced two sets of true leaves, the outdoor soil has warmed, and the last frost date has passed, the heirloom tomato seedlings are ready to be hardened by sitting outside in the shade for about a week or two. After hardening, the heirloom tomato plant should be planted in a small trench with the plant lying on its side and buried up to the first set of leaves so it will develop a strong root system along this stem and produce a hardier plant. Heirloom tomatoes should be watered very consistently, about every two to three days.
Growing heirloom tomatoes are more susceptible to the cold than other varieties. The hardening process will help them toughen so they can endure the stress of changing weather patterns, wind, and extremes with less damage. About a week or two before planting, tomato plant seedlings should be placed in a shady part of the garden in an area protected by the wind for about 30 minutes. This can be increased each day by about an hour until they are out overnight on a night when there is no danger of frost. The plants can gradually be exposed to more wind and watered more frequently as they are exposed to sunlight.
Growing heirloom tomatoes in containers is similar to growing heirloom tomatoes outdoors. The bottom third of a 15-gallon (about 57-liter) container should be filled with compost. The heirloom tomato plant should be set deeply into the container and buried up to the first set of leaves. All buried leaves should be pinched off before burying so the plant doesn’t direct nutrients to them. Heirloom tomatoes planted in a garden can be transplanted in a similar way, buried up to the first set of leaves.
To prevent blossom end rot and cracked fruit, heirloom tomatoes should be watered consistently. Watering should be done only when the soil has dried out an inch or two beneath the surface. Too little water will result in less fruit, while too much watering may result in cracked and split fruit. When growing heirloom tomatoes, inconsistent watering will result in blossom end rot. Heirloom tomato plants should be mulched with grass clippings or commercial mulch. Tomato plants may be fertilized with a balanced fertilizer when planting and once after the first small fruit appear.