Planting Tomatoes From Seed

Learn how to grow tomatoes from seed.

Not much beats a sun-ripened, garden-fresh tomato. If you’re someone who salivates at the thought of sinking your teeth into that first luscious ‘mater of the season, take your experience to the next level by planting tomatoes from seed.

Tomato Seedlings

Tomato Seedlings

Starting tomato seedlings in peat pots minimizes transplant shock because you plant both the seedling and pot.

Photo by: Gardener’s Supply Co. at Gardeners.com

Gardener’s Supply Co. at Gardeners.com

Seed starting isn’t hard, and it gives you a chance to get some dirt under your fingernails while winter still has its chilly grip on your garden. Learn how to grow tomatoes from seed with this back-to-basics tutorial.

Timing

Most experienced seed-starting gardeners sow tomato seeds indoors anywhere from 5 to 6 (but up to 8) weeks prior to their region’s last average frost date. Check your frost date here. You can usually get by with a five- to six-week start, which is ample time to grow stocky seedlings with plenty of leaves. If you’re raising seedlings in a greenhouse or high heat (more than 70°F) setting, reduce your start time by one week. (Warmth makes plants grow faster.) With a longer start time, you risk getting leggy seedlings and will likely need to repot seedlings several times.

Soil

Tomato Seedlings In Deep Pots

Tomato Seedlings In Deep Pots

Choose deep pots for growing tomatoes from seed. Peat pots minimize transplant shock because you plant both the seedling and pot.

Photo by: Gardener’s Supply Co. at Gardeners.com

Gardener’s Supply Co. at Gardeners.com

Fill your containers with a seed-starting mix—a soilless mix that likely has a peat or coir base. This type of mix drains well and is usually sterile. Typical garden soil, on the other hand, doesn’t usually drain well and often hosts disease organisms. Don’t use it for seeds.

Containers

Give Tomato Seedlings Larger Pots

Give Tomato Seedlings Larger Pots

For the healthiest, strongest, biggest tomato plants, shift seedlings to larger pots as they grow.

Photo by: Gardener’s Supply Co. at Gardeners.com

Gardener’s Supply Co. at Gardeners.com

Seed starting containers don’t have to be fancy—as long as they hold soil and drain water, you can use them to grow tomatoes from seed. Many gardeners upcycle yogurt cups or half-gallon milk jugs for starting tomato seeds. Others like plastic seed-starting cell packs or biodegradable pots. Any of these systems works. The ideal tomato seedling is a short, stocky, leafy plant with a well-developed root system, which forms best when tomatoes are in deeper pots.

Tomato Seedling Roots

Tomato Seedling Roots

Compare root systems of tomato seedlings grown in shallow and deep peat pots.

Photo by: Jeff Clarke for Gardener’s Supply Co. at Gardeners.com

Jeff Clarke for Gardener’s Supply Co. at Gardeners.com

To cultivate a deep root system, transplant seedlings to deeper pots as the plants grow taller. Before transplanting, remove lower leaves and bury the seedling up to the growing point. New roots will form along the buried stem.

Sow Seed

Plant two to three seeds per container, covering them with about a quarter inch of soil. Press gently to make sure seeds are firmly touching soil.

Water

Moisten the top layer of soil. Dribble water in slowly or use a mister of some sort. Cover the moist potting mix with a clear cover to create a greenhouse effect and help keep soil moist. Some seed starting kits have plastic lids that fit on containers. Otherwise, use a piece of kitchen-style plastic wrap.

Turn Up the Heat

Seeds germinate fastest in warm soil. Put your seed-starting pots in a warm spot, or use heat mats—plastic, waterproof mats that work like a heating pad. Set seed pots on the mat, plug it in, and the mat gently warms soil. The ideal air and soil temp for germinating tomato seeds is 70°F minimum.

Check

Check your seeds daily, watering as needed. Seeds need to be kept moist to germinate, but you also don’t want too much water. Vent your pot cover occasionally to avoid having beads of water running down onto soil. Tomato seeds germinate anywhere from a few days for early varieties to 10 days for other types. When you spot little green sprouts, remove covers from pots and shift seeds off heat mats into bright light—either a bright window, sunporch or grow light.

Grow On

To finish with healthy tomato seedlings, keep soil consistently moist—don’t overwater, but don’t let it dry out, either. Rotate pots near windows so seedlings don’t stretch to reach light. Thin multiple seedlings by removing weaker ones—snip stems with scissors. Repot seedlings if they seem to outgrow their containers before they’re ready to go in the garden.

Why Start Seeds

Oxheart Tomato

Oxheart Tomato

Oxheart tomato is also known as cuore di bue, which is Italian for “ox heart.” This meaty heirloom tomato makes a flavorful sauce and is yummy on sandwiches.

Photo by: National Garden Bureau at NGB.org

National Garden Bureau at NGB.org

Growing tomatoes from seed can be a money-saving venture, reducing your bill at the garden center. But one of the main reasons to try growing tomatoes from seed is to gain access to unusual tomato varieties, including heirloom types like oxheart (above). More tomato types exist than you can typically find sold as seedlings. Seed starting lets you taste old-fashioned and unusual varieties and also helps preserve genetic diversity. 

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