How to Grow Heirloom Tomatoes From Seed

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If I walked up to random vegetable gardeners and asked what they were planning to grow this season, the safe money would be placed on heirloom tomatoes.

Most everyone can readily find uses for the classic tomato in salads, sauces, juices, cocktails, breaded and fried, placed in a pie, and my personal favorite, the BLT. Few of us don’t like tomatoes, but to those who do not, I give my sincerest apologies.

Some veteran gardeners out there have an unofficial competition around who can produce the first vine-ripened tomato of the season. This blog entry isn’t for them; it’s for the folks who want to move beyond the Beefsteak and Super 100 transplants from their local garden center and try their hand at raising some heirloom tomatoes from seed.

Determine the last frost date for your region

Contact your area’s extension service or garden center, or better yet, ask a gardening neighbor familiar with your local conditions. What you’re looking for is an estimate of when it’s safe for tender plants to be outside without getting nipped by a damaging frost. Also, you could Google it.

When to Plant Heirloom Tomatoes Outside

Got that last frost date? Okay, now add two weeks to it. That’s the earliest date you can plant your tomatoes outside.

Tomatoes grow like gangbusters when the temperatures are warm. Planting them outside when temps are still cool only slows their growth rate.

When to Sow Heirloom Tomato Seeds Indoors

With that date in mind, now count backwards 6 to 8 weeks. This is about the time you want to plant your tomato seeds. For me in Boston, last frost is roughly May 3, giving me a plant-out date of May 17; count back 6 to 8 weeks and I should be sowing my tomato seeds indoors between March 22 and April 5. In comparison, someone in Charleston would be sowing tomato seeds around March 1.

Containers and Soil

Any container with a hole for drainage will do. If you’re reusing plastic plant or food containers, clean with a 10% bleach solution. Use a commercial seed starting mix available at your local garden center. Pre-moisten your starting mix (it’s easier to work with) and fill your trays or containers. Press down firmly to remove large gaps. You also can use those pre-filled Jiffy pots, they work well too.

How to Plant Heirloom Tomatoes

Plant each seed about an inch deep, gently press down on the soil, and give them a light sprinkle of water. Increase the humidity around your container or tray by placing a clear plastic bag around it loosely (leave a little opening for air to get in). Place in a warm location with indirect light. You might consider placing them on top of a warm major appliance or on a special heating mat available from garden centers or online suppliers.

Seeds should germinate in about 7-14 days with consistent conditions of 70F-80F. Keep an eye on the trays. Once your seeds germinate, remove the plastic bag.

Tomatoes Need Sun

Keep growing at 70F-80F once the seedlings germinate. The more light, the better your heirloom tomato seedlings will be.

If all you have is a windowsill, that’s fine. Your seedlings will turn toward the light coming in the window, so be sure to give the containers a turn every day or two to keep them growing straight.

Also, try to minimize drafts sneaking through the window. If you can, set your seedlings under fluorescent stick lights, such as those used in a workshop, for 14 hours a day. Position the lights about 6 inches above the seedlings. And remember, seedlings grow up! You’ll have to either adjust the lights to move upward or adjust your tray’s bench to move downward.

Keep in mind, seeds will germinate more slowly if temperatures are cooler than 70F-80F. Add a week to your calculations if that’s the case.

These seed-starting tips will work for pretty much any vegetable that seed companies recommend starting indoors. Some veggies you can plant directly in the ground! Look for that info soon.

Meet Ellen Wells

When you’re raised on a farm, you can’t help but know a thing or two about gardening. Ellen Wells is our expert on edible gardening.…

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