Generally speaking tomato and pepper seedlings are ready to be planted outside in the garden about 6 weeks following germination. It is a huge benefit if seedlings are “potted up” from their original small cells into slightly larger pots before planting outside. Potting up tomato and pepper seedlings is best done around the 4-week stage (or when they have 2 sets of true leaves).
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Transplanting tomato seedlings from small containers into larger pots, a process known as up potting, is an important step to growing healthy, productive tomato plants. Getting the timing right for up potting is crucial – doing it too early or too late can negatively impact growth. In this comprehensive guide, we’ll cover everything you need to know about when and how to up pot your tomato seedlings.
Why Up Pot Tomato Seedlings
Up potting serves several key purposes
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Prevents seedlings from becoming rootbound. Tomato seedling tap roots can quickly reach the bottom of small starter cells or pots If seedlings are left in these cramped quarters for too long, the roots tangle and curl, strangling the plant. Up potting gives the roots room to continue growing strong
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Corrects leggy seedlings. Sometimes tomato seedlings can get stretched out and leggy due to insufficient light, excessive heat, or overcrowding. Up potting offers an opportunity to bury leggy stems deeper, allowing roots to form along the buried stem and a sturdier, bushier plant to grow.
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Boosts growth with a larger root system. When up potting, some of the seedling stem gets buried in the new container. This stimulates the plant to generate adventitious roots along the buried stem. More roots means more ability to take up water and nutrients, fueling faster growth.
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Saves space. Large pots take up precious real estate. Keeping seedlings in proportionally sized pots conserves room while still meeting the needs of small plants.
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Avoids overwatering. Seedlings in an oversized pot risk being overwatered. Excess moisture in the soil can lead to fungal issues. A properly sized pot provides sufficient but not excessive water.
When to Up Pot Tomato Seedlings
Timing is critical when up potting tomato seedlings. Do it too soon and you shock the tender young plants. Wait too long and seedlings suffer from cramped, tangling roots. Ideally you want to up pot when:
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Seedlings have 2-3 sets of true leaves. The first set of seed leaves (cotyledons) don’t count. Wait for the second set of true bipinnate leaves to emerge.
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Roots are just starting to reach the bottom of the starter cell or pot. Check by gently tugging up on a seedling. If roots are already crowding the bottom, it’s time to up pot.
This optimal window generally falls 2-3 weeks after seeds germinate, but exact timing depends on variety and growing conditions. Fast growing cultivars in warm environments may need up potting on the early side. Slower varieties in cooler temps can wait a bit longer before up potting.
Pay close attention and let the seedlings themselves tell you when the time is right. Carefully pop a few out and inspect root development across your crop. Up pot any that meet the size and root growth criteria outlined above.
How to Up Pot Tomato Seedlings Step-by-Step
With the timing sorted out, let’s walk through the up potting process from start to finish:
Gather Supplies
- Seedling tray or other starter pots
- New larger pots – 3-4 inch pots are ideal for tomatoes at this stage
- Potting mix – Can use normal mix now instead of seed starting mix
- Watering can or bucket
- Tray or surface to work over
- Plant labels and marker
Prepare New Containers
- Fill larger pots about 2⁄3 full with moistened potting mix
- Using your finger or a pencil, make an indentation in the center of each pot
- Label pots to keep track of varieties
Remove Seedlings from Starter Pots
- Support soil plug from below and ease seedling out
- Avoid tugging seedling by the stem which can damage plant
- Try to keep root ball intact
Transplant Seedlings
- Place root ball in prepared indentation in new pot
- Position plant so only 2-3 sets of true leaves remain above soil line
- Bury some stem to stimulate root growth from buried section
- Backfill around root ball with more moistened soil
Water Newly Potted Seedlings
- Gently water new pots to settle soil and eliminate air pockets
- Allow pots to drain fully before returning plants to growing area
Provide Adjustment Period
- Keep newly up potted plants out of direct sun for a day or two
- Allow roots to establish before resuming regular care regimen
- Hold off fertilizing until seedlings are settled into new pots
Proper up potting technique minimizes shock and encourages vigorous growth. Handle seedlings gently, keep roots moist, and provide a little extra care as plants adjust to roomier quarters.
With the timing mastered and process executed properly, up potting sets your tomato crop up for success. Seedlings transplant readily and soon take off with their expanded root systems. A little effort up front pays off all season long with stronger, healthier plants.
Up Potting Best Practices
Follow these tips for seamless up potting and robust tomato seedling development:
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Up pot in the morning or evening when temperatures are cooler. Avoid the hot afternoon sun.
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Work quickly but gently to keep seedling roots moist and minimize stress.
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Water seedlings thoroughly after up potting to remove air pockets and evenly moisten soil.
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Allow time for an adjustment period before exposing newly potted plants to full sun and wind.
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Let seedlings dry out slightly between waterings. Overwatering newly potted plants is easy to do.
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Hold off fertilizing until seedlings recover from transplant shock, then resume at half strength.
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Monitor for signs of stress like wilting, yellowing leaves, or stunted growth. Baby plants if needed.
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Once up potted, fast growing tomatoes will soon need either another size up or transplanting into final garden location.
What’s Next After Up Potting Tomato Seedlings
Congratulations, your tomato seedlings are situated in roomy new quarters and ready to take off growing. Make the most of this fast growth stage with these tips:
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Move newly potted seedlings back under grow lights or into sunny window. Keep light levels bright.
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Water when top inch of soil is dry. Check pots daily and don’t let seedlings wilt.
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Transition to balanced fertilizer like fish emulsion or compost tea. Feed weekly at half strength.
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Prune lower leaves or “suckers” to concentrate energy; leaving 6-8 leaves per main stem.
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Monitor temperature and harden off plants before moving outdoors. No direct sun or cold nights!
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Transplant into final garden location after last frost when seedlings are 6-12” tall.
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Plant deep with only top 2-3 sets of leaves above soil to establish stronger plants.
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Add support structures like cages or stakes after transplanting.
With a little attentive care, your up potted seedlings will thrive through the transplant process and beyond. Just be sure to keep a close eye on their needs and time all transitions carefully. Vigilant gardeners are rewarded with vigorous tomato plants and bountiful harvests.
How to handle tender seedlings when transplanting:
- Handle the seedlings by the leaves rather than the stems. If you tear a leaf, the plant will still grow. If you break the tender stem, the plant is ready for the compost pile.
- I grow my initial heirloom tomato plants in 196-cell trays, and when it is time to pot up I take a butter knife and gently pop the plant out of the cell with the soil bundle (aka a plug) intact. Have a 4″ pot ready with moist potting soil and make a hole with your finger in the center of the soil in the 4″ pot. Place the seedling plug into this hole and gently press the soil around it to make contact with the roots.
- If you grow many seedlings in one large container rather than in cells, you will need to tease apart the roots from each seedling and then place in the hole of the 4″ container. Alternatively, you can snip off the weaker seedlings at the soil line and leave the strongest plant in the container to take advantage of the nutrients in the remaining soil. Remember…don’t handle the seedlings by the stem!
When to Transplant Seedlings from Seed Tray to Larger Pots
Although the 4-week timeline for potting up seedlings is a good benchmark, another sign that they are ready is when they have two sets of true leaves (do not count the set of “seed leaves” at the bottom).
Depending on the weather and when you are going to put the heirloom tomato plants in their permanent bed, you may want to pot up a second time. A good rule of thumb when deciding when to do the second transplant is to wait until the height of the seedling is three times the diameter of its pot (probably around 6-10″ tall).
When to Pot Up (Repot) and Transplant Tomato Seedlings
FAQ
When should I transplant tomato seedlings to bigger pots?
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What are true leaves?The first leaves that emerge are called cotyledons and are not true leaves. True leaves are the second set of leaves that appear on the plant.
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Why transplant?Transplanting to larger pots allows the root system to have more room to develop, which is crucial for healthy growth.
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Timing:Aim to transplant when the seedlings are 3 inches tall and have their first set of true leaves.
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Tips for transplanting:
- Let the pots dry a bit so the soil is easy to work with.
- Gently pull the plants apart, handling them only by their leaves, not their stems.
- Bury the stems deeper than normal to encourage root growth from the stem.
- Let the pots dry a bit so the soil is easy to work with.
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When to transplant into the garden:Larger tomato seedlings should be transplanted once the last chance of frost has passed and the weather during the day sits comfortably at 65-70 degrees F.
When should I pot on my tomato seedlings?
After a couple of weeks, once the seedlings have a couple of true leaves, move them into individual pots or modules of peat-free multi-purpose compost.
When should I pot up my seedlings?
Once the seeds have germinated and have two sets of true leaves, it is time for fertilizer and less heat. So this can be a good time to pot up.
When can I transplant seedlings from a seed tray?
As a general guide, after your seeds germinate they can grow in smaller (1.5″ cell trays) for about 2-3 weeks, in larger 2″ trays they can grow in them for about 3-4 weeks before needing to be transplanted.
How do you plant a tomato plant in a potting mix?
Moisten the potting mix and sow seeds about 1/4 inch deep and 1 inch apart. Cover the container with plastic and place in a warm sunny location with consistent temperatures between 70°F and 75°F. Keep soil evenly moist but not soggy and do not allow it to dry out.
How do you repot tomato seedlings?
Then, when you need to repot your seedlings, use a well-draining soil optimised for tomatoes. Tomato seedlings like to live in warm daytime temperatures ideally ranging from 21° to 27° C (70° to 80° F). Sustained temperatures over 29° C (85° F) can start to strain your young plants.
Can you plant tomato seedlings in pots?
You’ve sowed the seeds. Now it’s time to plant tomato seedlings into their own pots. Tips on pricking out tomato seedlings, planting them into individual pots, and growing them on using grow lights. Includes an instructional video. This is part two of the Growing Tomatoes from Seed Series.