When you grow tomatoes from seed, you grow many plants for the same amount of money you'd spend on just a few plants from the garden center.
You also have access to HUNDREDS of different tomato varieties – cherry tomatoes, paste tomatoes, slicers, heirlooms – in nearly every color of the rainbow.
We'll walk you through the steps to grow tomatoes from seed, and then get into planting details and troubleshooting some common problems.
- 10 Steps to Growing Tomatoes from Seed
- What's the Difference Between Determinate and Indeterminate Tomatoes?
- Which Potting Soil to Use to Grow Tomatoes from Seed
- Marking Seedlings
- When Should I Start My Tomato Plants?
- Containers for Starting Tomato Seedlings
- How Deep Should I Plant My Tomato Seeds?
- Getting the Tomato Seeds to Germinate
- Can I Use Old Old Tomato Seeds (Left Over from Previous Years)?
- Transplanting Tomato Seedlings to Larger Pots
- Hardening Off Your Tomato Seedlings
- Planting Tomatoes in the Garden
- Troubleshooting Common Problems When You Grow Tomatoes from Seed
10 Steps to Growing Tomatoes from Seed
- Choose the right tomato varieties for your garden.
- Start seeds six to eight weeks before average last frost date.
- Use good seed starting mix and label your containers.
- Plant seeds 1/4 inch deep, and keep soil moist but not soaking wet.
- Use bottom heat to improve germination, but grow plants at cool room temperature. (Remove heater when sprouts appear.)
- Keep seedlings in a sunny window, or use a grow light for more consistent lighting. Turn off light at night (or use a timer) to let plants rest.
- Add a fan to provide gentle movement and strengthen stems.
- Move seedlings to larger pots as they grow.
- Harden seedlings before moving them to the garden.
- Plant deep in fertile soil with full sun and water well.
What's the Difference Between Determinate and Indeterminate Tomatoes?
Indeterminate plants continue to grow and set fruit until frost – mine commonly reach six feet or more in height.
Determinate plants will grow to a more modest size (they may not require staking). They set all their fruit at roughly the same time and are ready for harvest during a narrow window of time.
Most heirloom varieties are indeterminate, while many modern hybrids are determinate.
Comparing indeterminate to determinate tomato seedlings, the indeterminate on the left is taller and leggier, while the determinate plant is smaller and stockier.
Which Potting Soil to Use to Grow Tomatoes from Seed
My favorite potting mix is FoxFarm Organic Potting Soil, which contains worm castings and other organic fertilizers right in the mix.
You can also make your own potting soil mixes, if you are so inclined.
I mark my seedlings using popsicle sticks broken in half. Popsicle sticks are cheap, durable, and can be tossed in the compost when they are no longer needed.
When Should I Start My Tomato Plants?
Start your seedlings inside about 6 to 8 weeks before your average last frost date. This helps you get a jump on the growing season, which is especially important for cold climate gardeners.
Check out the post When Should I Start My Seeds? Printable seed starting calendar to get a schedule for seed starting, hardening and planting out to the garden.
Containers for Starting Tomato Seedlings
I save the black plastic pots that you get from the greenhouse. They fit neatly in seedling trays (and under my grow lights on my seed starting shelves).
They also have drainage, last for many years, and stack easily for storage at the end of the season.
If it holds dirt and allows drainage, you can probably use it to start seeds, so use what you have available.
How Deep Should I Plant My Tomato Seeds?
As a rule of thumb, you want to plant seeds roughly three times as deep as the seed is wide, so tiny seeds stay on or near the surface, and larger seeds go a little deeper.
Plant tomato seeds around 1/4 inch deep, and gently tamp down the soil around the seeds.
Getting the Tomato Seeds to Germinate
Cover the seeds with a clear plastic cover, and put them in a well lit location. I like to give them a little jump start with a seedling heating mat underneath, since they like a little extra warmth to get going.
Can I Use Old Old Tomato Seeds (Left Over from Previous Years)?
Yes, you can use old seeds when you start tomatoes from seed.
Tomato seeds generally store quite well, but the germination rates decrease over time. Plant extra seeds to compensate for reduced germination.
Transplanting Tomato Seedlings to Larger Pots
It's fine to start with several baby tomato plants in one pot, but once they get true leaves, they need room to grow.
You can clip off extra seedlings at ground level and leave the healthiest plant, but I prefer to give each plant it's own spot.
When repotting, transplant seedlings as deep as possible in their new container. This will help support the stems. Yes, it's okay if bottom leaves are covered.
In a few weeks, I graduate the plants to the larger pots.
Hardening Off Your Tomato Seedlings
When it's getting close to the time to plant them outside, start hardening your tomato plants.
“Hardening off” gently introduces plants to outside weather to toughen them up enough to survive in the garden.
I prefer to harden plants off over 3-4 days, starting them out with no more than an hour or two of direct sun the first day and increasing exposure each day. Make sure they are protected from the wind and adequately watered when you set them out.
Planting Tomatoes in the Garden
After the danger of frost is over and you've hardened off your seedlings, it's time to move them to the garden.
Plant tomatoes deep, and they grow new roots from the buried stem. I leave about 1/3 of the plant above ground.
Add a balanced fertilizer with calcium to the planting hole. Avoid excess nitrogen (manure), which promotes more leaves but less fruit.
I also mulch, trellis and often add a soaker hose under the mulch for watering.
To get the full scoop on planting and TLC for your best tomato crop ever, visit Growing Tomatoes (Organically) – 11 Tips for Success.
Troubleshooting Common Problems When You Grow Tomatoes from Seed
Sometime when you grow tomatoes from seed, your little seedlings fail to thrive. We cover some common problems below.
Tomato Seedlings Drop Dead
Once your seedlings emerge, uncover them within the first 24 hours. Keeping them covered can lead to damping off.
Damping off results from fungal infection. It generally comes from keeping your seedlings too wet. One day they'll look fine – then WHAM – the seedlings are laying there dead.
Generally the stem shrinks up near ground level, and the soil is very wet. Sometimes here will be mold or fuzz growing on the surface of the soil.
A sprinkle of cinnamon or a spritz of chamomile tea may help save the remaining seedlings, but once a plant has keeled over, it's a goner.
To help prevent damping off, some folks sprinkle sand over the dirt when they plant seeds. If you maintain proper moisture levels and good circulation, damping off shouldn't be a problem.
Tomato Seedlings are Pale or Yellow
If the color of your seedlings is off – check moisture levels. You want damp soil, not too wet or too dry.
If the moisture level seems fine, try a soil test. Some commercial potting mixes can have too much or two little fertilizer.
Tomato Seedlings are Skinny and Flop Over
If your seedlings are really tall, skinny and floppy (also known as “being leggy”) – chances are your lighting is inadequate. Try a different location or more artificial lighting.
Alternatively, you can run your hands lightly across the tops of the seedlings from time to time during the day. Proper lighting is the first step, but movement will help, too.
More Gardening Articles
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- 5+ Terrific Tomato Trellis Ideas
- 4 Reasons Your Tomatoes Are Not Ripening + How You Can Help
- 7 Tips to Stop Blossom End Rot and Save the Harvest
- Tomato Flowers But No Fruit, or No Tomato Flowers – 9 Troubleshooting Tips
- How to Start a Garden – 10 Steps to Gardening for Beginners
There are also a wide array of tomato preserving recipes, including:
Originally published in 2011, last updated May 2020.