Tomato and pepper seedlings are usually ready to be planted outside in the garden about 6 weeks after they sprout. Before planting seedlings outside, it is very helpful to “pot them up” from their small cells into slightly bigger pots. It’s best to pot up tomato and pepper seedlings when they are 4 weeks old, or when they have two sets of true leaves.
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Growing tomatoes from seed? One important step is transplanting your seedlings into larger pots at the right time. Up potting tomato plants properly ensures they grow into strong productive plants. Follow this guide to understand when and how to up pot tomato seedlings.
Seedling Growth Stages
Tomato seeds usually take 5-12 days to germinate and emerge as seedlings after sowing. The young seedling goes through several stages of early growth:
Cotyledon stage – The first “seed leaves” that initially emerge. At this stage seedlings are surviving off the energy stored in the seed.
First true leaves – The first set of normal tomato leaves after the cotyledons. True leaves begin photosynthesizing energy from light.
Second set of true leaves – The next set of leaves that form as the plant continues growing. More leaf sets will continue to develop.
When to Up Pot
Tomato seedlings are ready for their first up potting when they develop their second set of true leaves. This generally occurs 3-4 weeks after sowing the seeds.
Up potting at this stage encourages further root growth to support the developing foliage. Delaying transplanting can result in stunted plants with compromised root systems.
Ideally, tomato seedlings should be up potted 2-3 times total before their final move outdoors to the vegetable garden. Here’s a guide to up potting schedule:
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3-4 weeks after sowing: Transplant seedlings into 3-4 inch pots when the 2nd true leaves emerge.
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2-3 weeks later: Up pot again into 1 gallon pots.
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2 weeks after that: Final up pot into 2+ gallon pots before hardening off and garden transplanting.
Make sure seedlings are watered well both before and after transplanting to reduce transplant shock.
Signs Seedlings Need Up Potting
How can you tell for sure it’s time to size up into larger pots? Watch for these cues:
- Roots visible through the drainage holes or bottom of pots
- Plants becoming top heavy or floppy
- Soil drying out much faster than normal between waterings
- Slowed or stunted growth
Any of these signs indicate a need for more root room and nutrition that larger pots provide.
Potting Mix for Up Potting
Use a good quality potting soil meant for seed starting and transplants when up potting tomato seedlings. Avoid heavy garden soils. Recommended mixes:
- Peat or coir based mix fortified with perlite or vermiculite
- Soilless blend of peat/coir and perlite/vermiculite
- Compost or worm castings based mix
Potting mixes provide proper drainage and air pockets for healthy roots. They are lightly fertilized for seedlings’ nutritional needs.
When up potting, thoroughly moisten soil first. Carefully make a hole and place seedling inside, filling in around stem. Firm soil gently and water well after transplanting.
Fertilizer Needs After Up Potting
Potting soils contain enough starter fertilizer for young seedlings. About 2-3 weeks after up potting, you can begin applying a mild liquid tomato fertilizer once a week.
Choose an organic fertilizer made for vegetables at half strength. This provides nutrients for actively growing plants without risk of burn.
Once hardened off and transplanted in the garden, tomato plants can be fed with a balanced organic granular fertilizer as needed.
Providing Proper Light
Getting adequate sunlight is crucial for stocky, healthy seedlings after up potting. Here are some lighting guidelines:
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Place pots in a south facing window or under grow lights. Tomatoes need 12-16 hours of light per day.
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Keep lights 2-4 inches above plants. Adjust height as plants grow.
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Rotate pots regularly so all sides of plants receive light exposure.
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Prepare to harden off seedlings before garden transplanting to acclimate to sunlight.
With the proper up potting timing, techniques, light and care your tomato seedlings will transform into robust, productive plants!
Common Up Potting Mistakes
Here are some common errors to avoid when up potting tomato seedlings:
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Not transplanting into larger pots quickly enough. This stunts root growth.
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Skipping the second up potting. Tomatoes need room for extensive root systems.
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Allowing seedlings to become rootbound or pot-bound. This restricts nutrient and water uptake.
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Using heavy garden soil instead of proper seedling potting mix. Garden soil compacts and retains too much moisture for seedling roots.
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Fertilizing too soon or with too much. Seedlings only need mild fertilization. Too much can burn roots.
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Crowding seedlings after up potting. They need good air circulation and space to grow.
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Letting new transplants dry out. Seedlings are prone to wilt quickly until established.
Key Takeaways
Follow these important tips when up potting tomato seedlings for best results:
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Transplant into larger pots when 2nd true leaves emerge, around 3-4 weeks after sowing.
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Use proper potting soil made for seedlings – not garden soil.
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Water seedlings well before and after up potting to prevent shock.
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Ensure adequate light from a sunny window or grow lights after transplanting.
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Wait 2-3 weeks after up potting to begin mild fertilizing.
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Time final up potting 2 weeks before hardening off and garden transplanting.
With the right up potting approach, your homegrown tomato seedlings will thrive!
When to Transplant Seedlings from Seed Tray to Larger Pots
The 4-week mark is a good guideline for when to pot up seedlings, but 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).
If the weather is bad or you don’t know when to put the heirloom tomato plants in their permanent bed, you might need to pot them up again. Most of the time, you should wait until the seedling is three times the diameter of its pot tall before doing the second transplant. This means that the seedling should be about 6 to 10 inches tall.
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. The plant is ready for the compost pile if you break the weak stem.
- I start my heirloom tomato plants in 196-cell trays. When it’s time to pot them up, I use a butter knife to carefully pop the plant out of the cell while leaving the soil bundle (also called a plug) in place. Prepare a 4-inch pot with wet potting soil, and use your finger to make a hole in the middle of the soil in the pot. Put the seedling plug in this hole and gently press the soil around it so that the roots can get to it.
- If you grow many seedlings in one big pot instead of in cells, you will need to pull the roots of each seedling apart and then put it in the pot’s 4′′ hole. If you’d rather, you can cut off the weaker seedlings at the soil line and leave the strongest plant in the pot to use the nutrients in the remaining soil. Remember…don’t handle the seedlings by the stem!.