No matter what climate you live in, growing tomatoes from seed always starts out the same way: figure out the best time to plant relative to your last frost date, start the seeds indoors, then transplant the seedlings after germination.
But where and how you transplant tomato seedlings makes all the difference between a mediocre tomato plant, and a staggeringly productive tomato plant that barely lets you keep up with it.
So what’s this trick that helps your tomato seedlings grow bigger and better from the get-go?
Transplanting the seedlings into bigger pots first, before you transplant them in the garden.
And you can do it while you wait for the soil outside to warm up.
What are the benefits of repotting tomato seedlings?
Repotting tomato seedlings might feel like unnecessary work if you just want to move things along, but there’s a good reason for it: This extra step allows you to take advantage of their remarkable talent to grow roots along their stems.
Tomato seedlings are unique in that they like their stems buried deeply. They have the ability to form new roots (called adventitious roots) along their stems, which help the plants grow more vigorously.
In fact, if you live in a humid climate, you may have even noticed adventitious roots forming above ground from tiny bumps (nubs) on the stem.
(I like to call them “air roots,” and contrary to what many people think, the fuzzy hairs on the stems do not turn into roots themselves — they contain the oils responsible for the distinctive smell of tomato leaves.)
Yes, every single one of those bumps has the potential to be a root!
Given ample moisture and sunlight, these roots will continue to grow like the ones underground and can even plant themselves in the soil if they get long enough.
Transplanting tomato seedlings deep in the soil stimulates the adventitious roots and creates a larger and healthier root system that will take up more nutrients and anchor your plant when it finally goes in the ground.
When should you repot tomato seedlings?
Tomato seedlings are ready to be transplanted when they are at least 3 inches tall, and have their first true leaves, which are the second and subsequent sets of leaves that appear.
The first leaves that sprout (called cotyledons) are not leaves at all, but embryonic structures from the seed that provide nutrition until the seedling can make its own food.
Cotyledons naturally drop off after a few days once the true leaves unfold and begin the task of photosynthesis, making way for adult growth on the plant.
You should also pot up leggy tomato seedlings to keep them from stretching any further and growing pale and spindly. Burying the stems will strengthen them and encourage new root development.
How to repot tomato seedlings in 4 easy steps
Step 1: Gather the supplies you’ll need to repot your tomato seedlings.
Start with clean 4-inch pots and pre-moistened, high-quality potting mix (you can also make your own potting mix at home).
Don’t skip this step. Peat-based potting mixes are difficult to wet thoroughly when they’re completely dry, and you could end up with uneven moisture or water that just drains out the pot without being absorbed.
If several seedlings are growing in the same pot, some people will snip off the extras and keep only the strongest seedling, so as not to disturb the roots during transplant.
But if you transplant the seedlings before they become root bound, it’s easy to separate tomato seedlings without harming them (especially if all the seedlings appear healthy).
Step 2: Remove the seedlings from their seed starting pots.
Water your seedlings to loosen up the potting mix and keep the roots moist while you work.
If you started your seedlings in newspaper pots, unroll them. The roots should be nicely developed but not twisted around each other.
Step 3: Separate the seedlings.
Always handle tomato seedlings by their leaves, not their delicate stems. If a leaf pulls off, chances are it will grow back. But if the stem snaps, your seedling can’t be saved.
Separate the seedling by gently pulling on its leaves and wiggling it away from the potting mix. The roots should release easily.
Let the moist potting mix cling to the roots to protect them from drying out.
Step 4: Place a seedling in each pot and bury the stem up to its lowest set of leaves.
Position the tomato seedling in the center of the pot so that the lowest set of leaves is even with the rim of the pot.
Fill the pot with pre-moistened potting mix and gently pat it around the seedling to hold it in place. Tap the pot a few times on your work table to settle the potting mix, and add more as needed until the pot is filled to the top.
Water the seedling until it drains freely out the bottom.
Repeat Steps 1 through 4 for the remaining seedlings.
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4 tips for taking care of your tomato transplants
1. Let your transplants acclimate under dappled light or party cloudy weather.
To minimize transplant shock, keep your tomato seedlings out of harsh direct sunlight for a day or two. Try to pick a period of calm weather so your transplants aren’t subjected to downpours or strong winds right away.
2. Don’t overwater your seedlings.
Tomato plants are susceptible to overwatering, so keep the potting soil barely moist at all times. Water deeply to reach the roots at the bottom (or soak pots from the bottom up), and only water again when the first inch of the soil feels dry to the touch.
3. Feed your tomato seedlings with an organic fertilizer.
Even when they’re this small, tomato plants are heavy feeders (plants that need a lot of nitrogen and other nutrients to thrive).
Start setting the stage for vigorous growth by fertilizing tomato seedlings with liquid fish and seaweed emulsion (which gives them an instant shot of nutrients) or top dressing them with a granular vegetable fertilizer (which releases nutrients slowly over several weeks).
4. Transplant your tomato a second time for better root growth.
A tomato plant can be repotted two or three times before it’s transplanted in the garden, each time with more of its stem buried.
Moving the plant into a larger container at each transplant phase (for example, from a 4-inch pot to 1-gallon pot to 3-gallon pot) encourages the roots to keep branching out and form a robust, healthy mass.
Once your seedling grows up to three times the height of its pot, follow my guide on why and how to transplant your tomato plants a second time.
Growing Tomatoes From Start to Finish
- Grow Tomatoes Like a Boss With These 10 Easy Tips
- How to Grow Tomatoes in Pots — Even Without a Garden
- Fish Heads Are the Secret to Growing the Best Tomatoes
- How to Repot Tomato Seedlings for Bigger and Better Plants
- Why and How to Transplant Tomatoes (a Second Time)
- How to Transplant Tomatoes in a Trench: A Gardener’s Trick for Tall Plants
- Florida Weave: A Better Way to Trellis Tomatoes
- Save the Harvest: How to Fix Blossom End Rot on Tomatoes
- Tomato Leaves: The Toxic Myth
- Smells of Summer: Fresh, Fragrant Tomato Leaves
- The Power of Fermenting and Saving Tomato Seeds
This post updated from an article that originally appeared on April 7, 2011.