How to Grow Heirloom Tomato Plants

heirloom tomato harvest

The Spruce / Autumn Wood

Heirloom tomatoes are annual vegetable plants that have not been crossbred or hybridized for at least 40 years. They are open-pollinated, meaning the seeds will produce plants identical to the parent plant. This means you can save your heirloom tomato seeds and grow the same tomatoes next year. Heirloom tomatoes need a bit more care than standard hybrids (which are bred primarily for growing performance rather than flavor), but they tend to have thinner skin, juicier flesh, and better flavor than most hybrid varieties.

Like the many hybrids, heirlooms are fast-growing, but the plants need 60 to 80 days or more to produce ripe fruit. They are best planted in spring (after the threat of frost has passed) as transplanted seedlings or small plants bought from a garden center. If you live in an area with a long growing season, you might have success direct seeding heirloom tomatoes in the garden, provided you start them early enough.

Botanical Name Solanum lycopersicum
Common Name Heirloom tomato; open-pollinated tomato
Plant Type Annual, vegetable
Mature Size 5-8 ft. tall
Sun Exposure Full sun
Soil Type Loamy, well-drained
Soil pH Slightly acidic (6.0-6.8)
Bloom Time Summer
Flower Color Yellow
Hardiness Zone 1-13 (USDA)
Native Area South America
Toxicity  Toxic to pets

How to Plant Heirloom Tomato Plants

Depending on whether they are early or main-season varieties, you should space your heirloom tomatoes between 2 and 3 feet apart. The soil should reach the first set of leaves—setting deeply like this will strengthen the support for these tall-growing plants.

Tomatoes are frequently grown alongside basil as it is an excellent natural fly repellant, and chives and mint are thought to improve flavor. Potatoes, however, can also suffer from blight, so don't plant them in the same space.

Heirloom Tomato Plant Care

Light

When it comes to sunlight, heirloom tomatoes are one of the hungriest plants out there, along with plants like sunflowers or corn. These are plants that need full, direct, unfiltered sunlight all day long. Pay attention to any shadows cast by neighboring trees or buildings when you plan your tomato patch.

Soil

Healthy soil is a critical component of thriving heirloom tomato plants. They will yield the greatest harvest in rich, loamy soil that allows roots to penetrate deeply. If your soil is heavy clay, use raised beds or container culture. Add compost, leaf mold, or manure up to fifty percent to blend with the native garden soil.

Water

Keeping your tomatoes well-watered is a must for heirloom tomatoes, especially once they set fruit. Watering deeply will encourage deep root systems. Assuming you did a good job preparing the soil, drainage should be excellent, so keep an eye on the moisture level and never let plants dry out. Allowing the soil to vacillate between moist and dry causes problems in fruit development, including cracking and blossom end rot. Use drip irrigation to further limit airborne diseases like blight.

Temperature and Humidity

Heirloom tomatoes need warm temperatures to grow. Planting them too early won't give you earlier fruits; wait until night temperatures are at least 60 degrees Fahrenheit before planting outdoors. Humid conditions don't bother heirloom tomatoes.

Fertilizer

Heirloom tomatoes are heavy feeders and need regular fertilizing to bloom and fruit. Organic and chemical balanced all-purpose fertilizers are both acceptable and a matter of personal preference.

unripe heirloom tomatoes
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heirloom tomato ready for harvest
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checking an heirloom tomato for harvesting
The Spruce / Autumn Wood
Heirloom Tomato Plants
Fabio Pagani/Getty Images

Varieties of Heirloom Tomatoes

There are hundreds of varieties of heirloom tomatoes, and the cultivar names are as colorful as the fruits themselves.

  • Brandywine is a gateway variety for many new to heirloom tomato gardening. The giant pinkish-red ruffled fruits, tender skin, and juicy complex flavor might remind you of a piece of Willy Wonka chewing gum. They have sweet, followed by tangy and spicy, followed by savory and umami flavors, all in one magnificent bite
  • Black Krim tomatoes originated from Krim, Russia, and quickly gained a wide following with their sweet, robust flavor and handsome maroon fruits
  • Aunt Ruby's German Green tomatoes stay green until harvest, which might fool hungry squirrels but not your tastebuds. These large beefsteak tomatoes are the perfect blend of sweet and tangy

Heirloom Tomatoes vs. Hybrid Tomatoes

Heirloom tomatoes and hybrid tomatoes look the same and have the same growing requirements. However, you cannot save seeds from hybrids and expect them to grow true-to-type. Check your plant or seed packet labels if you wish to save seeds.

Brandywine Tomatoes
Posinote/Getty Images
Black Krim Tomatoes
Campbell Downie/Getty Images
Aunt Ruby's German Green Tomato
cristina.sanvito/Flickr/CC BY 2.0

Harvesting

Heirloom tomatoes are ready to be picked just before their color peak. Leaving them on the vine too long encourages cracking. Tomatoes that stay green upon ripening can be a little tricky to judge; usually, the color shifts from flat mint green to bright chartreuse or streaky green. The fruits will also soften as they approach their peak.

heirloom tomato harvest
The Spruce / Autumn Wood 
heirloom tomato harvest
The Spruce / Autumn Wood 

How to Grow Heirloom Tomatoes in Pots

Heirloom tomatoes growing in containers will need more frequent watering and fertilization than those growing in the ground. Use a large 24-inch pot for healthy root systems. Fertilize every two weeks with an all-purpose 10-10-10 fertilizer.

Pruning

Pruning heirloom tomatoes can increase plant productivity in the garden. Remove suckers at the plant base to direct energy to produce fewer but larger fruits. Heirloom tomatoes grow quite large and need staking for support. By reducing the number of fruiting branches down to four or five with pruning, your plants will be manageable, and individual fruits will be larger.

Propagating Heirloom Tomatoes

Tomato cuttings root readily. As you prune away suckers, plant them in the soil or root them in water. They will form roots and begin to grow as separate plants within a week.

How to Grow Heirloom Tomatoes From Seed

Heirloom tomatoes are easy to grow from seed. Use moist, sterile potting mix, and press the seeds lightly into the soil. Germination takes place in about a week if temperatures are between 70 and 75 degrees Fahrenheit.

Potting and Repotting

Use premium potting soil for potting tomatoes. Plants will need frequent repotting in warm weather, so check the drainage hole for roots to prevent plants from becoming root-bound.