Repotting seedlings 101

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In late spring, I am a repotting queen! I use plug flats and cell packs to start my vegetable, flower, and herb seeds – they’re extremely efficient in terms of space – but, they don’t offer a lot of root room. After 6 to 8 weeks under the grow lights, many of the seedlings need to be repotted into larger containers to ensure continued healthy growth until it’s time to move them into the garden.

You’ll know your seedlings are ready to be repotted when their roots have filled their current containers and their foliage is crowding out the neighbours. Still not sure? Use a butter knife to pop a plant out of its pot and take a peek at the roots. If they’re well developed and encircling the soil ball, it’s time to repot.

Moving your seedlings to larger containers will help ensure a healthy root system and top-quality transplants for your garden. New containers should be about twice as large as the old ones.

repotting

This geranium seedling is ready for repotting. Note the well developed root system.

Repotting 101:

  • Gather all your materials (pots, potting soil, tags, waterproof marker, butter knife) first so that repotting is quick and efficient.
  • Water seedlings before starting. Moist soil will cling to the roots, protecting them from damage and drying out.
  • No tugging! Don’t pull the baby plants from their cell flats or plug trays. Use a butter knife, narrow trowel, or even just a long nail to prick the seedlings from their containers.
  • If there is more than one seedling in your container, gently tease them apart for repotting.
  • Place them in the new pot, lightly tamping the soil.
  • Have a stack of labels ready to go and give each pot a fresh tag. Alternatively, use a waterproof marker to write the name of the plant on the side of the pot.
  • Water with a diluted liquid fertilizer to settle the roots in the new soil and encourage healthy growth.

Do you have any more repotting tips to add?

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20 Responses to Repotting seedlings 101

  1. Cindi says:

    What transplants are safe to plant out in a tunnel and what should we be seeding in the garden now. With this snow sprinking this morning, i’m confused!

    • Good question! Yes, wasn’t that snow wonderful.. sigh! Anyway, any of the cool and cold season crops can be planted now – direct seeded in your tunnels.. or transplanted, provided they have been hardened off properly. Spinach, kale, lettuce, peas, endive, Asian greens, beets, carrots, etc.. The tunnel is a good idea.. just be sure to vent the ends when the temp outside is above 4 C and it’s sunny.. you don’t want it to get too hot in there! 🙂

  2. James R. Skinner says:

    I understand that some seedlings don’t like to be re-potted and should be started started in 4″ pots instead? Is there somewhere I can find a list of those vegetables.. I think its mainly cucumbers and squash?

    • Great question James! I don’t have a list – maybe a future article? – but you’re right… cucumbers and squash don’t like to be re-potted and so should be planted in 4 inch pots and moved to the garden carefully. It’s also important to not seed these too early in spring. Usually 3-4 weeks before the last frost date is ideal. Niki

    • James R. Skinner says:

      Thanks Niki. Does pot size and start date apply to Cucamelons as well? Halifax Seed packet says sow inside 6-8 weeks prior to last frost date.

  3. Yes, that’s exactly right! I started my cucamelons yesterday and give them about 6-8 weeks under the grow lights. They are also sowed in 4 inch pots because they grow quickly. 🙂

  4. Michelle says:

    Riffing what others have asked. I often start in larger pots planting 4 -5 seeds rather than the wee little multi cell flats. Is this a no-no, and if so why?

    • It’s not a no-no, but it’s not as space efficient as using flats/trays.. plus, 4 inch pots are deeper – this can reduce the need to water, but if you’re growing slow-growing seeds like peppers and the soil stays overly damp for an extended period, the plants can be more prone to rot. I like to grow fast-growing plants of those that don’t like transplanting in 4 inch pots – cucamelons, squash, and gourds for example. Otherwise, I aim to start my seeds in flats/trays. I can also fit many more under my grow lights when grown in flats/trays, and the roots don’t need to be separated/pulled apart/disturbed when there is one plant per cell, unlike having a handful in a 4 inch pot. Some plants don’t mind being separated, but others do (cucumbers for example). I think this would make a great post idea – maybe I’ll do a whole post on it 🙂 Thanks for your question! – Niki

  5. What if you don’t have a grow light can you use anything else? When do I take the plastic cover off from the top once it started growing

    • Great question Cathy – take off the plastic cover as soon as the seedlings germinate. You want to ensure good air circulation around them. The plastic will help hold moisture and humidity to encourage quick germination, but once the seed sprout, remove it. A grow-light is best but mine are simple 4-foot fluorescent shop lights, so if you have a florescent bulb in your house, you can put your plants close to it. But ideally, a florescent bulb should be just 2-3 inches away from the plants. You can also buy a simple spot light grow bulb that screws into a normal mixture. They’re usually only about $15-20. Or, find a sunny, south-facing window to give them as much natural light as possible. Hope that helps! 🙂 – Niki

  6. Liza says:

    Helpful info! I started my tomato seedlings in a germination soil. They are in need of a bigger container before they are ready for outside. Should I still use the same soil or a potting mix for veggies?

    • Great question Liza! If you already have it, that soil is perfect. No need to buy another bag. If you need more, you could get some veggie potting mix. I usually use Pro-Mix, but there are many good quality potting soils. Hope that helps! – Niki

  7. Tina says:

    What type of soil do I use for re-potting?

  8. Monica S. says:

    Can I continue to use seed starting mix for the soil when I re-pot? That’s what I’m using for germination

  9. Sherry L Middaugh says:

    When I repot can I use a larger container and repot a few seedlings at a time? For tomatoes I will use smaller pots and only 1 seedling per pot but for peppers can I repot multiples?

    • Good question! You can transplant multiples into one larger pot. Tomatoes grow so quick so I like to give them their own pot, going from a cell pack to a 4 inch pot for example. If the peppers get too big for their shared pots though, you’ll need to re-pot once again. – Niki

  10. Erika says:

    I’ve started my cucumbers in small peat pots but I think they will need to be repotted into larger containers before they go out. Any advice on how to transplant from one peat pot to another? Should I break away the original peat pot from the roots first?

    • I would definitely break away the original peat pot and repot into the larger one. Don’t worry about breaking away some of the outside roots, they will re-grow quickly. Personally, I don’t use peat pots. I find they need to be watered a lot, grow mold on the outside pot surface, and you really can’t transplant them. You should remove them before you move your seedings into the garden. I prefer plastic, reusing for as many years as I can before recycling. Good luck!! 🙂 – Niki

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