5 Signs It’s Time To Repot Your Seedlings
It’s important to be able to recognize when it’s time to transplant seedlings from the seed tray to a larger pot. Transplanting seedlings a few weeks after starting should be part of your seed starting routine.
We start the seeds in smaller containers because we can control moisture and temperature much better that way, and if you’ve heard me talk much about seed starting then you know my motto is that moisture and temperature are the most important factors in getting good germination.
But once the seeds sprout, they quickly outgrow their seed starting container. It would be a bad idea to let them continue to grow in a pot that is too small. They’ll become nutrient deprived and their roots will grow round and round into a big knot.
Transplanting them into larger pots, helps them develop healthier roots and grow faster. By not restraining their growth indoors, you’re training them to grow big and strong when it’s time to put them in the garden.
But how do you know when to repot seedlings?
There are a few simple things you can look for that are dead giveaways your plants need a bigger pot.
1. They have one or two sets of true leaves
The ideal time for transplanting your seedlings is about 3 weeks after they sprout or when you have 1-2 sets of true leaves. It’s better to get them in new containers before they start to show the signs of stress listed below.
2. The cotyledons are turning yellow and falling off
Cotyledons are the first leaves that emerge from a seed. They are different than the “true leaves.” True leaves are the second and subsequent sets of leaves that grow after the cotyledons emerge.
It is normal for cotyledons to yellow and fall off, but if they’re doing it when you only have 1 or 2 sets of leaves, your plants really need to be transplanted.
3. The true leaves are turning yellow
It’s definitely time to transplant if the true leaves are yellow. This is a sure sign that your plants are starved for nutrients.
4. The roots are wound around and around the root ball
You definitely want to see roots in your growing medium when it’s time to plant, but if they’re circling around the edges of the root ball, then they’re getting too crowded.
5. They’re crowded
You don’t want to overcrowd your plants when they’re young. Some plants will grow taller than others and that will affect how much light the others get. You’ll also get the larger plants sequestering all the nutrients and that will stunt the growth of your other plants as well.
Why transplant the seedlings at all?
You might wonder why we would go to the trouble of repotting seedlings at all? Why not just give them some fertilizer, or better yet, start them in a larger container to begin with?
You’ll be much more successful germinating seeds if you start them in small containers. This allows you to have more control over the temperature and moisture in the seed starting container. We’ve found we have much better sprout rates in the smaller cell trays as compared to using other types of seed starting containers.
You can dose your plants with some fertilizer but that will stimulate growth. They’re already telling you they need more space, why stress them by making them grow bigger in the same small space?
Both of those options are viable alternatives, but you’ll have healthier plants if you transplant instead.
How to repot seedlings
Transplanting seedlings is quite easy to do. You simply need a new container and some potting mix. We recommend a container that is twice as big as what they are in now and a high quality potting mix like Fox Farm Ocean Forest.
We like to mix the potting mix and the seed starting mix in a 50:50 ratio. This is especially helpful for young seedlings who still have tender roots.
Before filling your containers, wet down your soil mixture to ensure even watering after you plant. Then nest your seedling in the new container, filling in around the base of the plant and pressing down to seat it in well and remove air pockets.
For tomatoes, bury the stem leaving only 1 or 2 sets of leaves above the soil line. For all others, plant them level or bury the stem about 1/4 inch or less.
Water your transplanted seedlings well and place them back under the light.
What about fertilizing seedlings?
You can fertilize young seedlings after transplanting as needed. Use a liquid organic fertilizer diluted to half strength. If they tolerate the half strength and seem like they need more, you can up it to full strength.
Don’t fertilize your seedlings until after you transplant them. You don’t want to stimulate growth in a space that is too small.
Do you transplant or repot your seedlings?
Tell us about your experience in the comments below!
You've conquered seed starting. Woot! But do you know when to repot seedlings? Transplanting seedlings is a step you can't skip! Learn the signs your plants are telling you they've outgrown their seed starting tray.
Potting Up Seedlings: What, Why, When & How
If you started plants from seed, chances are you will need to pot up the baby seedlings before they get transplanted into the garden. Maybe even twice! Your individual potting up needs and timing will vary. It will depend on the size of the seedling containers you started with, how quickly your plants are growing, and how long it is from the time they sprouted until they need to go outside. The act of potting up, when done right, helps your plants thrive!
This article will discuss the what, why, when, and how of potting up. At the end of this post check out the demonstration video! It shows our process for potting up tomato and cucumber seedlings
If you’d rather skip the reasoning and timing behind potting up, click below to jump straight to the “how-to” and video.
What is Potting up?
Potting up couldn’t get any more literal. It is simply the act of transplanting seedlings “up” into larger containers than they were previously living in.
To be honest, potting up is a task I dread for some reason. It isn’t all that difficult, but does take a little time and effort. Over all the other things I need to do around the homestead, this is one chore that I consistently put off until it’s urgently due. Knowing this about myself, we try to combat this and set ourselves (and plants) up for success from the very beginning – by starting seeds in larger containers. This reduces the urgency to do it so soon after germination. We’ll talk more about container sizes shortly.
Why Pot up?
Potting up seedlings as they grow provides them the best chance to grow stronger and bigger, feel less stressed, and live their best life!
1. By potting up seedlings into larger containers, it enables their roots to continue to grow without getting root-bound. A root bound-plant is not a happy plant. When a plants roots are being restricted to the point that they start to grow in circles around themselves, they become tangled and “bound up”. This can reduce the roots ability to spread out and flourish after they’re planted out in the garden. Plant health is directly tied to root health, so this means the plants are also less likely to flourish.
Plants with tight, bound root balls can be gently loosened during the time they’re transplanted. However, this could either help them, or harm them. Some plants don’t mind a little root-ruffling, and breaking up that ball can encourage the roots to spread as we want them to. However, some don’t take a liking to this treatment. They might even get a bit of transplant shock from it. Therefore, we try to prevent root binding in the first place, to reduce the amount we need to disturb the roots later.
2. Another reason to pot up seedlings is that as their roots grow larger, they drink more water, and thus dry out more quickly. You’ll notice that a small 6-pack full of soil and yet-to-sprout seeds will retain moisture much longer than a small 6-pack full of maturing, thirsty seedlings. Taking care of seedlings can be tedious enough, but especially so if they’re drying out on you every day!
3. Lastly, the potting up process feeds the seedlings! If you started seeds in straight seedling mix, or a mix with primarily seedling soil like we do, chances are they’re hungry. Seedling soil is very fluffy and pretty devoid of nutrients. Even if you have been feeding with an occasional dilute seaweed extract, the plants will definitely enjoy a slighter richer, heartier soil now!
When to Pot Up
The timing for when to pot up is going to vary from gardener to gardener, situation to situation, and plant to plant. The factors that influence the best time for potting up seedlings include their container size, the type of plant, when they’re intended to be planted outside, and how vigorously they are growing. There is no set rule like, “You must pot up within 33 days of germination”…
The best time to pot up a seedling greatly depends on the size of container you started it in. Smaller containers, like those trays with dozens of cells each, are going to require potting up sooner. Plants will feel cramped and overgrown in those fairly quickly. As I mentioned before, we usually avoid starting larger vegetable seedlings in tiny-hole trays. By starting them in slightly larger containers, like these reusable 4” nursery pots, we don’t need to pot up until about 6 to 8 weeks after germination. After that, we’ll move them into 6-inch or 8-inch pots.
The various seedling containers we use. We’ll usually start seeds in the 6-packs or smaller round 4″ pots, and then pot up to the 6″ pots and 8″ pots as needed. All of the supplies we use are durable and reusable, which we sanitize between seasons.
Then why don’t we just start seeds in those larger 6 to 8 inch containers from the get-go, you ask? That way, we don’t need to pot up at all, right? Well, it’s not quite that simple. First of all, if you start seeds in huge containers, it’s going to take up a ton of space. You will not be able to fit nearly as many containers on your heat mats and under grow lights, which is pretty crucial during germination and the first few weeks of life. That means less plants, which is never a good thing.
Also, tiny seeds and seedlings don’t necessarily want to be swimming in a huge sea of soil. It is easier to overwater, and their roots might struggle to develop. They do like to be hugged, just a little. Plus, moving from a seedling start mix into richer soil is a great growth-encouraging step – one we’d miss out on if we started in big pots.
Type of plant
The timing for potting up also depends on the plant itself. Larger plants like tomatoes will more quickly outgrow their space than something smaller like herbs started in the same size container. Tomatoes grow much faster than peppers, so we always need to pot up our tomatoes earlier.
If you plan in advance, you could try to start certain vegetables, herbs, and flowers in appropriate size containers. For example, we start most of our flowers, herbs and leafy greens in 6-packs, and the other bigger veggies in 4” pots. We have found that by doing this, the flowers and herbs are usually okay in their 6-pack until the time they need to go outside, and may not need to be potted up at all. Squash grow very quickly and don’t like their roots disturbed. Therefore, we start those straight in larger 6” pots to give them plenty of space. We start them only about 3-6 weeks before they’ll be planted outside, so we don’t need to pot them up at all.
Timing to plant outside
Another variable that impacts potting up is when your target transplant date is. If you intend to plant out all your seedlings in the next week or two, then don’t bother! That is, unless they’re getting really really overgrown and bound, then it might be worth it. Especially if planting is still two weeks away. Yet if your plants are showing signs of being cramped in their containers and it is still several weeks or more until plant-out time, pot those babies up!
A few weeks after germination, start keeping an eye on the bottom of your seedling containers. Are roots starting to poke through the bottom drainage holes? How big is the plant looking? Does it still look happy? Has it still been growing steadily, or has it slowed?
When the roots start to poke through the bottom of the container a lot, it is time to pot up into a larger size. Can’t see the roots sticking through the bottom, but the seedling seems pretty large? Carefully take one out of the container and look at its root ball! Sometimes they’ll start to spiral around themselves before they come through the bottom. I should also note that you don’t have to wait until the roots are coming through the bottom, or until it is close to being root bound. You can pot up sooner too! I just always seem to wait until the last minute.
Just a modest root peep show.
How to Pot Up
Find or obtain some containers that are slightly larger than the ones they’re already in. About twice as large is a good goal. If you’re going from super-tiny cells, even more than twice as large would be most efficient, reducing your need to do this again.
Now it’s time to give the seedlings some fresh, rich soil to play in! You could go two ways here. Again, this depends on your situation.
Soil for Potting Up
When we are potting up fairly large, established seedlings like the tomato in this example, we use a high-quality organic potting soil, straight from the bag. Something like this planting mix from G&B Organics, or this potting mix from Kellogg Garden Organics. You can see that it is quite a bit more dense, textured, and rich than the seedling start mix the plant was previously living in. At this stage in maturity, they can handle it! Not just handle it, but love it. Pre-moisten the soil if possible.
However, if you are potting up very small, less established seedlings that have thin fragile roots and no solidly formed root ball, they will probably like something a little more fluffy added in the mix still. In that case, it would be best to combine something like 60% organic potting soil and 40% of your favorite seedling start mix. That way, their tender roots meet less resistance when they’re trying to grow.
Add a little soil into the bottom of the new container, and gently ease the plant out of the smaller container without pulling on the seedling itself. Place its entire soil mass and roots into the new container. Then fill in around the sides with the new soil mix.
To Bury or Not to Bury? That is the question.
If the seedlings have gotten a bit tall and leggy, it is okay to plant most kinds of seedlings deep, filing soil up around the stem and burying it a bit. This is totally safe (and even preferred) for tomatoes. The portion of the buried tomato stem will actually shoot off new roots! You could also do this for other members of the nightshade family, including peppers, potatoes, and eggplant. Brassicas (the cabbage family, including kale, broccoli, and collard greens) and cannabis can also handle a little burying. Especially when they’re bigger and the stem is more firm. See the images below as an example.
As you can see, we buried the tomato stem with several inches of soil. It will now grow roots from that portion of the stem. When we transplant it outside, we’ll bury it by another couple of inches in the garden beds too.
Other types of plants may not like this practice. The now-buried stem could rot and kill the plant. This is particularly true for beans and trees, so keep the soil line about the same as it was previously. I would also avoid burying seedlings that are still very small and tender, regardless of their variety. I have read mixes messages about burying cucumbers. Overall, I think it is okay but not as commonly encouraged as with tomatoes. If you do, only bury them up to their first set of leaves, or just a couple inches.
To avoid the need to bury seedlings and therefore any risk of rotten stems, the best practice is to prevent leggy seedlings in first the place. To do this, provide ample light and other ideal seed-starting conditions. If you’d like to learn more about seed starting best practices along with ongoing seedling care, read here!
A Neat Potting Up Trick:
I learned a fun little trick a few years ago, which is demonstrated in the video and photos below. It can be used for potting up seedlings, especially ones that you do not want to bury the stems of). However, we most often exercise this trick when we are planting bigger plants like shrubs or small trees in to pots. The idea is to make a dummy hole, or a placeholder for the root ball, inside the container that the plant is being transferred in to.
Fill the new, larger container with the amount of soil you estimate should go below the plant. Then set the plants current container down inside the larger one. You can use an empty one, if you have something the same size on hand, or actually place the plant itself (still in the pot) down in there. Is it at the right level? Keep in mind things usually sink down a little after time and watering. If so, lightly pack soil in around the outside of the inner pot, creating a nest of soil. This trick works best with pre-moistened soil, reducing the likelihood it will cave in on you. Then you can pull out the dummy container, gently ease the plant out and into its new perfectly-sized hole!
By doing this, you are ensuring there are no air pockets and a nice amount of soil around the plant. Thus, it reduces the need to try to stuff soil in around it afterwards. Depending on the container or pot you’re working with, that can sometimes be difficult or awkward. It also reduces the jostling and possible shock to the plant being transplanted. Before we learned this trick, I don’t know how many times we accidentally overfilled containers and then had to pull or dig the plant back out to adjust the soil amount. If you’re working with a large, heavy plant, or one with a not-very-solid root ball, this can be a pain in the butt.
The dummy-hole trick. Look at how perfectly that cuke seedling root ball fits right in the hole! Lightly cover with a little more soil after, making sure it doesn’t have any voids.
After Potting Up
Give them a good water! We prefer to water from below, allowing the soil to soak up water from the tray beneath it. The seedlings may also appreciate some dilute seaweed extract in their water, which can help to ward off transplant shock. To read more about fertilizing seedlings with seaweed extract, check out this post!
Who wants a drinky drinky? Mama’s buyin’.
That’s really all there is to it folks.
The freshly transplanted seedlings can now live happily in their new spot for several weeks, until they move in to their forever home – your garden. Don’t forget to harden off indoor seedlings before transplanting outside to prevent transplant shock!
Check out the potting-up demo video:
This post is proudly supported by Kellogg Garden Organics.
This article will discuss the what, why, when, and how of potting up seedlings. The act of potting up, when done right, helps your plants thrive!