How to Transplant Young Seedlings

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Time to move your seedlings to larger quarters. But how? Photo: greenbeanconnection.wordpress.com

If you have young seedlings that are packed too tightly in their original pot and want to transplant them into more spacious containers, here’s how to do it.

First, understand that seedlings can be transplanted into individual containers, such as pots or cell packs, or into larger shared containers, such as seed trays. Many gardeners, though, take advantage of this step to transplant their seedlings into cell packs, plastic reusable inserts composed of multiple individual growing compartments (6, 9, 12, etc.). The advantage of these cells is that the seedlings will be later easier to remove with their root ball fully intact when the time comes to transplant them into the ground or an outdoor container.

Step by Step

1. First prepare the planting container(s). Wash them (if recycled) and fill them with pre-moistened potting soil up to about half an inch (1.5 cm) from the top.

2. With a pencil or spoon, form a hole in the center to receive the seedling’s root ball.

3. Take the seedling between thumb and forefinger by a leaf (or cotyledon), never by the stem. (If you accidentally tear or crush a leaf, the seedling can grow a new one; if you damage the seedling’s only stem, it will die). With the other hand, slip a pencil or spoon into the soil under the seedling and, using the tool like a lever, push up while gently pulling on the leaf. The seedling will come out intact with a root ball covered in potting soil.

4. Gently set the root ball into the hole you prepared, at the same level as before. (You can bury more deeply, up to the level of the first leaves, those seedlings that have the capacity to form roots on their stem, such as tomatoes, peppers and cucumbers, plus cabbages and their relatives: broccoli, cauliflower, kale, etc.)

5. Fill the planting hole with potting mix and tamp down slightly.

6. Water very gently from above to complete the transplantation.

7. Place the seedling in a somewhat shaded spot for 24 to 48 hours before putting it back into full sun so it has time to acclimatize to the change. If you grow under a plant light, though: no acclimation period is necessary: you can put it back immediately under the light, less intense than the sun.

Extra Dense Seedlings?

Dense clumps of seedlings need special treatment. Photo: http://www.gardengatemagazine.com

Sometimes there are not just a few seedlings to divide, but a mass of them growing so densely together that separating them individually by the method above just won’t be feasible. If so, dig up the whole clump with a spoon and place it in a basin of tepid water as deep as the root ball is high. 

The potting mix will start to fall away on its own, but you can also help by swishing the water back and forth a bit. Soon, the soil will almost entirely drop off and previously tangled roots will unravel as if by magic. You can then lift each seedling out of the water, again holding it by a leaf and supporting its roots with a pencil or spoon, then continue transplanting it as indicated above.

Illustrations by Claire Tourigny from the book Les semis du jardinier paresseux.

Do you have to transplant seedlings indoors?

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Popular belief to the contrary, potting seedlings up is not always necessary. Photo: goingtoseed.wordpress.com

Question: Do you have to transplant seedlings started indoors into larger pots or can you keep them in their original pot until it’s time to transplant them directly into the ground?

Stephane Brousseau

Answer: Moving a seedling from a small pot or a tray into a larger one is called potting up and it used to be considered a necessary step in starting seedlings indoors. Certainly, my father believed in it and I can remember us sitting around his workbench and carefully transplanting dozens of little seedlings from trays into individual pots. It was believed at that time (that would have been about 50 years ago) that potting up stimulated better root growth and gave plants greater vigor. 

Years later, I began to test out this idea myself. I’ve always been a lazy kind of guy and planting seedlings into larger pots before transplanting them into the garden seemed like a doubtful extra step to me. So, I sowed some seeds into individual pots right away and others in trays like my dad did, moving them into the same size individual pots when the tray filled in. And guess what? The plants planted directly into the right-sized pots did at least well as the up-potted ones and generally quite a bit better, producing larger plants with stronger stems. 

Later, when the Internet came out and I was able to look at the results of actual scientific experiments, this confirmed I had been discovering. Transplanting inevitably slows the progress of young seedlings, most likely because it damages their roots. In general, the plants eventually recover from the transplanting and go on to produce normally, but sometimes the shock of this first transplanting reduces the productivity of the plant throughout the entire summer!

Logically, therefore, it’s better to avoid transplanting indoor seedlings into larger pots if possible.

The Right Pot

Check your seedlings to make sure they aren’t becoming root bound. Photo: homesteadandchill.com

I now try to sow my seedlings directly into a large enough pot to hold them comfortably until it’s time to plant them out. I sow 3 seeds per pot, then, if they all come up, thin to one plant per pot. Perfect! At least, that’s what I do unless planting-out time is delayed and I can see the seeds becoming rootbound* (never a good thing), in which case I confess to reluctantly potting up a few seedlings.

*You can tell a seedling is becoming rootbound when it dries out almost overnight and there are roots growing out of the drainage hole at the bottom of the pot.

After all, slowing the development of a young plant by keeping it in a pot that is too tight can seriously affect the results it will give once planted outdoors. Ideally, you should ensure that your plants keep growing smoothly and without stress until you can get them into the garden.

Six-pack for larger seedlings, like tomatoes and peppers (left) and for smaller seedlings, like lettuce and leeks (right). Photo: homesteadandchill.com

Small pots of 5 cm (2 in) in diameter or less are fine for plants that are naturally small or will only be growing indoors for a short time, such as lettuces, leeks and sweet alyssum, but 7.6 cm (3 in) pots may be necessary for tomatoes and peppers, even 10 cm (4 in) pots if you prefer to sow them early so the seedlings are larger at planting-out time. For some really large seedlings, such as castor beans, an initial pot size of 15 cm (6 in) may be necessary.

Do note, though, that not everyone agrees with me. You’ll see plenty of websites still offering the old information and insisting the potting up is essential. I suspect none of them have ever tried doing things differently.

If You’ve Underpotted

So, in my opinion, you only need transplant seedlings started indoors into larger pots if you have grown them in a pot that’s too small. Or if too many seedlings are growing in a tray and you want to recuperate all of them. And who doesn’t make that mistake every now and then?

You may want to sow seeds in small pots if space is at a premium early in the season, potting them up into more appropriate containers when more space becomes available. Photo: http://www.gardeningknowhow.com

Of course, maybe you purposely started your seedlings in small pots to save space. This is only logical if more growing space will open up later. For example, maybe you start growing your seedlings in an area where space is very limited, such as on a window sill or under a grow lamp, but have a greenhouse heated only by the sun that you can move them to when temperatures warm up further. In this case, the extra effort of transplanting your seedlings from tiny pots to bigger ones may well be worth it.

So, pot up if you have good reason to, but it’s an extra step a good laidback gardener would try to avoid.