Pot up tomato seedlings when their first true leaves open, usually 10 to 14 days after sowing, into pots about 3 to 4 inches across, burying the stem up to the leaves. Move them again only if roots fill the pot and planting out is weeks away. Enter your seedlings’ stage below to see whether to pot up now.
Try a preset:
Your entries stay in your browser. Nothing is sent to a server or saved to an account.
What Your Result Means: the verdict weighs how developed the seedlings are, how crowded the roots are, and how long they have before going outside. Seedlings move best while small, and a move is worth it only when there is time for the roots to use the new space.
When Should You Pot Up Tomato Seedlings?
At the first true leaves, while seedlings are small and recover quickly. Waiting too long in a crowded tray or tiny cell leads to tangled roots and stretched, weak stems.
- Check the leaves: true leaves are jagged and look like tomato leaves.
- Check the roots: slide a seedling out and look for roots circling the bottom.
- Count the weeks until you plan to plant outside.
- Read the verdict and move seedlings into 3 to 4 inch pots if it says so.
Tomato Seedling Pot-Up Timeline
| Stage | Typical Timing | What to Do |
|---|---|---|
| Seed leaves only | First week to 10 days | Wait; keep under bright light |
| First true leaves open | About 10 to 14 days after sowing | Pot up from trays or cells into 3 to 4 in pots |
| Roots fill the pot | Several weeks later | Move up a size if planting out is weeks away |
| Hardening off | About 1 to 2 weeks before planting | Skip potting up; harden off instead |
How Does the Pot-Up Checker Work?
Tray or cells + true leaves + 2 or more weeks to go -> pot up now
Roots circling + 2 or more weeks to go -> pot up a size
About a week to go -> skip it; harden off
3 to 4 inch pot, roots fine -> no need to move
How to Pot Up Tomato Seedlings
- Water the seedlings an hour before so the root ball holds together.
- Fill the new pot with moist potting mix and make a deep hole.
- Lift each seedling by a leaf, easing the roots out with a spoon or pencil.
- Bury the stem so only the leaves and growing tip sit above the mix.
- Firm gently and water in, then keep them out of strong sun for a day.
Worked Example
Say your seedlings are in a shared seed tray, 12 days after sowing, with one set of true leaves and planting out a month away. The verdict is pot up now into 3 to 4 inch pots. Lift each by a leaf, bury the stem up to the seed leaves, and water in. If they are still indoors in four weeks with roots circling, move them up a size.
Common Mistakes to Avoid
- Waiting too long: crowded seedlings stretch and tangle their roots.
- Holding the stem: it bruises easily; hold a leaf instead.
- Planting at the same depth: tomatoes root along buried stems, so bury them deeper.
- Jumping to a huge pot: a big pot of wet mix around small roots stays soggy.
- Potting up right before planting out: harden off instead.
Accuracy and Limitations
This is a practical guide, not a strict rule.
What It Does Well: applies extension timing for potting up to your seedlings’ stage and schedule.
What It Does Not Do: see your seedlings. Light, temperature, and variety all change how fast they grow. This is general guidance, not professional advice.
Methodology
Method: rule-based check of container, true leaves, roots, and weeks to planting out. Timing: transplant while small, about when first true leaves appear (University of Maryland Extension); when stems have straightened and first true leaves opened, usually 10 to 14 days after sowing (University of Nebraska–Lincoln); at one to three sets of true leaves (UConn). Technique: hold by the leaves; set seedlings with leaves and growing point just above the mix, burying most of the stem (Maryland; UConn). Pot size: 3-inch pots outperformed cell packs (Cornell). Feeding: most potting mixes feed seedlings for 5 to 6 weeks (Maryland); quarter-strength soluble feed once true leaves appear (UConn). Hardening off: about 1 to 2 weeks, matching our Hardening-Off Scheduler.
Sources: University of Maryland Extension – Care of Vegetable Seedlings, University of Nebraska–Lincoln – Growing Tomatoes in the Home Garden, UConn Home and Garden Education Center – Seed Starting, Cornell University – Avoid Transplant Shock. Last reviewed: September 28, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
When should I pot up tomato seedlings?
When the first true leaves have opened, usually 10 to 14 days after sowing. University of Maryland Extension notes seedlings handle the move best while small, around the time the first true leaves appear.
What are true leaves on a tomato seedling?
The first leaves are seed leaves (cotyledons), smooth and oval. True leaves come next and look like small, jagged tomato leaves.
What size pot should I move tomato seedlings into?
A pot about 3 to 4 inches across is a good first step up from a seed tray or cell pack. Cornell found transplants grown in 3-inch pots outperformed those from cell packs.
Can I bury tomato seedling stems when potting up?
Yes. Tomato stems grow roots where they are buried, so set seedlings deep, with just the leaves and growing tip above the mix. It also fixes leggy seedlings.
How do I handle seedlings when potting up?
Hold them by a leaf, never the stem, which bruises easily. Lift the root ball gently with a spoon or pencil.
Should I fertilize after potting up?
Most potting mixes feed seedlings for about 5 to 6 weeks. In a seed-starting mix without fertilizer, feed a quarter-strength soluble fertilizer once true leaves appear.
How many times should I pot up tomatoes?
Usually once, from a tray or cell into a 3 to 4 inch pot. Pot up again only if roots fill the pot and planting out is still a few weeks away.
Is it too late to pot up if I plant out soon?
If planting out is only a week or so away, skip it and harden the seedlings off instead; a move now adds stress without much benefit.
What are signs a seedling needs a bigger pot?
Roots circling the bottom or poking out of the drainage holes, the mix drying out very fast, and slowed growth or yellowing lower leaves.
Related Tomato Tools
See the Full Growing Tomatoes Guide
This checker gives general guidance on potting up tomato seedlings, not professional advice. Growing conditions vary; watch your seedlings and adjust. Spotted an error? Tell us here.