Plant heirloom tomatoes in spring after the last frost date, in a spot that gets at least six to eight hours of direct sun each day

Heirloom tomatoes need warmth to thrive—they won't germinate or grow well in cold soil. Wait until nighttime temperatures stay above 50°F consistently, which usually falls two to four weeks after your area's last spring frost. You can find your frost date by searching "[your city] last frost date" online, or by calling your local cooperative extension office.

Choose a location where tomatoes receive six to eight hours of direct sunlight daily. More sun means more fruit and better flavor. If your yard is shaded, heirlooms will struggle to produce. Avoid planting in the same spot where tomatoes, peppers, or potatoes grew the previous year, since soil-borne diseases can linger and attack the new plants.

Key Takeaways

  • Heirloom tomatoes need soil warmer than 60°F and air temperatures above 50°F at night before they will grow well.
  • Dig a hole deeper than the root ball and bury the stem partway up the plant—heirlooms will sprout roots all along the buried stem and anchor better.
  • Space plants 24 to 36 inches apart so air flows between them and prevents fungal disease.
  • Water deeply at the soil level once or twice a week rather than daily light sprinkling, which keeps foliage dry and reduces disease.

Prepare the soil before planting

Heirloom tomatoes are heavy feeders and need rich, well-draining soil. Before planting, mix compost or aged manure into the top 8 to 12 inches of soil—aim for about one-third compost to two-thirds existing soil. If your soil is clay-heavy and drains poorly, add compost to loosen it; if it is sandy and drains too fast, compost helps it hold moisture and nutrients.

Test your soil pH if you can. Tomatoes prefer soil between 6.0 and 6.8 on the pH scale. If your soil is too acidic (below 6.0), add lime; if too alkaline (above 7.0), add sulfur. A soil test kit from a garden center costs $10 to $20 and takes a few minutes. If you skip testing, straightforward adding compost will improve most soils enough for heirlooms to grow.

Dig the hole and plant the seedling

Dig a hole deeper than the root ball of your seedling—about 1.5 times the depth. Heirloom tomato stems will sprout roots all along their length if buried, which creates a stronger root system. Remove the seedling from its pot and gently loosen the roots with your fingers. Place it in the hole so that the lowest leaves are just above the soil surface, then bury the stem up to those leaves. The buried portion of the stem will develop new roots.

Backfill the hole with the soil-and-compost mixture you prepared, pressing gently so the plant stands upright and has good contact with the soil. Do not compact the soil hard—tomato roots need to breathe. Water thoroughly after planting so the soil settles and air pockets close.

Space plants far enough apart for air circulation

Plant heirloom tomatoes 24 to 36 inches apart, depending on the variety. Determinate (bush) types can be closer; indeterminate (vining) types need more room. Check the seed packet or plant label for the mature size of your specific variety.

Spacing matters because heirloom tomatoes are prone to fungal diseases like early blight and septoria leaf spot, which spread in humid, crowded conditions. Good air flow between plants keeps foliage dry after rain or watering, which slows disease. If you plant too close together, you will spend the summer fighting mold and rot.

Water deeply and infrequently rather than daily

Water heirloom tomatoes once or twice a week, giving each plant about 1 to 2 inches of water per week—enough to soak the soil 6 to 8 inches deep. Water at the base of the plant, at soil level, not on the leaves. Wet foliage invites fungal disease. A soaker hose or drip line works better than overhead sprinklers for this reason.

In hot weather, you may need to water twice a week. In cool, rainy weather, you may skip a week. The goal is to keep the soil consistently moist but not waterlogged. Stick your finger into the soil 2 inches deep; if it feels dry, water. If it feels wet, wait a few days. Inconsistent watering—dry one week, soaked the next—causes problems like blossom-end rot and fruit cracking.

Install support early to prevent root damage

Set up stakes, cages, or trellises at planting time, not later. Driving a stake into the ground after the plant is established can damage roots and set the plant back. Indeterminate heirlooms (the vining types that grow tall) need sturdy support—a 6-foot stake or a sturdy cage. Determinate types (bushier, more compact) can use shorter cages or stakes.

As the plant grows, tie the main stem loosely to the stake with soft ties like cloth strips or tomato clips. Avoid tying too tight, which can strangle the stem as it thickens. Prune suckers (shoots that grow between the main stem and branches) on indeterminate types to direct energy into fruit rather than foliage.

Fertilize every two to three weeks once flowering starts

Heirloom tomatoes need steady nutrition to produce well. Once the plant flowers, feed it every two to three weeks with a balanced fertilizer—something like 5-10-10 (nitrogen-phosphorus-potassium) or a tomato-specific formula. Follow the package directions for the amount; too much nitrogen pushes leafy growth at the expense of fruit.

You can use liquid fertilizer mixed into water, granular fertilizer sprinkled around the base, or compost side-dressed around the plant. Organic options include fish emulsion, seaweed extract, or bone meal. Stop fertilizing in late summer so the plant focuses on ripening fruit rather than growing new leaves.

Watch for common pests and diseases

Heirloom tomatoes attract hornworms (large green caterpillars), aphids, and spider mites. Check plants twice a week for damage. Hand-pick hornworms if you see them; they are straightforward to spot and remove. For aphids or mites, spray the plant with a strong stream of water from the hose, which knocks them off. If the problem persists, use neem oil or insecticidal soap, following label directions.

Early blight and septoria leaf spot are fungal diseases that cause brown spots on lower leaves. Remove affected leaves as soon as you see them, and do not compost them—throw them in the trash. Water only at the soil level, not on foliage. If disease spreads despite prevention, a copper fungicide can slow it, but the best defense is spacing, air flow, and dry foliage.

Frequently Asked Questions

Can I start heirloom tomatoes from seed indoors?

Yes. Start seeds indoors 6 to 8 weeks before your last frost date, in seed-starting mix under grow lights or a sunny window. Keep soil warm (70–75°F) and moist. When seedlings have two true leaves, thin them or move them to individual pots. Harden them off by setting them outside in a sheltered spot for a few hours each day for a week before planting in the garden.

What is the difference between determinate and indeterminate heirlooms?

Determinate heirlooms grow to a fixed size (usually 3–4 feet) and produce most of their fruit at once, then slow down. Indeterminate types grow tall (5–8 feet or more) and produce fruit steadily all season until frost. Check the seed packet to know which type you have; they need different spacing and pruning.

Why are my heirloom tomato flowers dropping without setting fruit?

Flowers drop when temperatures are too hot (above 90°F at night), too cold (below 55°F), or when the plant is stressed by drought or inconsistent watering. may support steady moisture and wait for temperatures to moderate. Flowers will set fruit again once conditions improve.

Do heirloom tomatoes need to be pruned?

Indeterminate heirlooms benefit from removing suckers (shoots between the main stem and branches) to focus energy on fruit. Determinate types need little pruning. Remove any diseased or damaged leaves at any time. Avoid heavy pruning that exposes fruit to sunscald.