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When to Pot Up Seedlings

Starting plants from seed is a good way to save money and get a head start on your garden. If you’ve started plants in seed trays you may be wondering how to tell when to move them into bigger containers.

Person potting up seedlings -- a necessary part of starting seeds indoors.

When to pot up seedlings is not always easy to recognize but you’re in luck. Here I’ve compiled a complete guide to help you figure out the best time to pot up seedlings including why pot them up in the first place, what signs to look for, and what containers to use.

Let’s get right to it!

What Does “Pot Up” Mean?

To pot up seedlings simply means to move them “up” into a bigger pot.

When starting plants from seed, many gardeners use plugs, seed starting trays, or other small containers to start seeds in.

Trays and plugs are a great way to maximize space and plant a lot of seeds at one time. They’re efficient because you can start a lot of seeds without using a lot of seed starting mix. Plus, you have more control over moisture levels and temperature with seedling trays.

Closeup of a starter tray of seedlings.  Knowing when to pot up seedlings means having strong and healthy plants.

As the seeds grow the plants eventually get too big for the small space they were planted in. This is when seedlings need to be potted up by being moved into a larger container.

If you’re wondering how to tell when seedlings are ready to be potted up, more information is below!

Is Potting Up Seedlings Necessary?

The short answer is it depends. In many cases it’s beneficial but there are times when it’s not necessary.

If you started seeds in larger containers late in the season then you may be able to move your plants straight into a garden bed rather than moving them into bigger pots.

If you started seeds in small containers or plug trays and the weather is still weeks away from being warm enough to transplant seedlings outside, you’ll definitely need to pot up those seedlings.

Biodegradable starter pots of seedlings being planted in a garden.

Benefits of Potting up Seedlings

There are several reasons why potting up seedlings is a good idea. If plants are not able to thrive in their current container, potting up provides a lot of benefits!

Give Proper Nutrition to Plants

Seed starting mix is designed to give seeds the best environment for germination. It’s not designed to feed small plants for weeks at a time.

Potting up seedlings allows you to move them into a more fertile growing medium that nourishes the plants as they grow.

Avoid Stressing the Plants

Seedlings that don’t have enough nutrients or enough room to grow become stressed and don’t grow as well.

You want your seedlings to be healthy, and not stressed when they go into the garden. Potting up seedlings gives your plants more room to grow and more nutrients resulting in healthier plants.

Increase Airflow

Having seedlings too close together restricts airflow between the plants. Restricted airflow can lead to mold which is harmful to plants.

By potting up and spreading plants out you can ensure proper airflow and reduce the risk of mold developing around the seedlings.

Give Plants the Best Chance of Success

The bottom line is, potting up seedlings keeps your plants healthy and gives them the best chance of success.

When to Pot Up Seedlings

Figuring out why potting up seedlings is beneficial is pretty straightforward. How to tell when it’s time to pot up seedlings is a bit tricker.

There’s no hard and fast rule for when to pot up seedlings because different plants grow at different rates and have different needs. However, there are a few things to look for that indicate it’s time.

With practice, you’ll learn to recognize the clues. Here are some signs to look for.

Plants are too Crowded

If you have several plants growing in one cell or container, chances are they’ll start to get crowded as they grow.

When seedlings become crowded, leaves may grow over each other and block the plants from getting enough light. Plants may push against each other or start bending. If you see any of these signs it’s a good indication that your seedlings need to be separated into larger containers.

Starter pots of seedlings.

Plants are Very Tall

Height is a good signal for when to pot up seedlings and it’s easy to identify. Seedlings taller than the height of the cell or container they’re planted in need to be potted up.

Roots Growing out of the Bottom

Roots growing out of the bottom are a sure sign that the seedling wants more space than it currently has. Give those roots some love and put them in a container with soil.

Leaves Turning Yellow

Yellow leaves are a sign that the plant is not getting enough nutrients. Remember seed starting mix is not designed to feed plants long term. Pot up yellowing seedlings into a bigger container with fertile soil.

Plants aren’t Growing

Seedlings that were growing well and then stall are another sign that the plants don’t have enough nutrients.

If your seedling looks healthy but doesn’t seem to be growing, putting it in a large container can help.

How to Pot Up Seedlings

Once you’ve done the hard part of recognizing when to pot up seedlings, the actual potting up is simple.

Potting up usually doesn’t take too much time and the whole process can be done in the same workspace where your seedlings are already growing. Bottom trays like the ones sold at Hoss Tools provide a good space to work.

The trays are large enough to hold your plants and a bag of soil. The tray is a good way to catch spills and avoid making a mess of soil all over your table or other workspaces.

Gather New Containers

Choose a container that’s at least twice as big as the one the seedlings are currently in. Compostable pots like the ones we found on Amazon are convenient because you can plant the entire container in the ground when it’s time to transplant seedlings outside.

Seedlings that have been potted up into biodegradable seed pots.

You can also reuse old containers or purchase a set of small pots. I like to save containers from plants I buy at the nursery. It’s cheaper than buying more pots and they can be used over and over again.

Prepare the New Pots

Fill your pots with a good quality potting soil and make a hole in the center large enough for the seedling. If the soil isn’t moist, premoisten it before adding your seedling to the pot.

Selecting Seedlings to Pot Up

You may not want to pot up every single seedling, especially if you’ve started an entire tray of the same plant.

Choose only the healthiest plants to pot up and discard the rest. It can be sad to let those little seedlings go but remember, it’s all part of the process. It’s better to have a few very healthy plants than to have a lot of unhealthy plants.

Separate Seedlings

If there are several plants growing in one cell the roots may be all tangled up. Separate the plants by gently pulling them apart. Be very gentle and try not to break the fragile roots.

A woman holding seedlings that are ready for potting up.

If the roots are too tangled, plants may not separate easily. In that case, it’s better to choose the healthiest plant and sacrifice the other one.

Forcibly pulling the roots apart can damage both plants. It’s better to have one healthy plant than two dead plants. To remove the extra seedling, use your fingers to pinch it off at the base of the plant and leave the roots intact. If the stem is too thick to pinch off, use scissors instead of your fingers.

Potting up Seedlings

Gently remove your seedling from its original container and put it in the prepared pot. Fill in around the plant with soil and press it down a bit to make sure there are no air pockets.

Potting up a seedling.

Water seedlings thoroughly and keep them under a grow light or in a sunny window until it’s time to transplant them outside.

Don’t Forget to Label the New Pots

Some seedlings look very similar such as squash and melons so it’s a good idea to label all of your seedlings.

I often think I’ll remember which plant is which and inevitably mix some up. Once I accidentally planted a pumpkin in the ground where I meant to put a cucumber (oops.) Learn from my mistake and label all of your plants!

These garden labels from Hoss are a great size and they come with a special garden marker so the labels won’t fade outside in the weather.

Harden of Plants Before Transplanting

To avoid transplant shock, make sure to harden off seedlings before moving them outside to their permanent home in your vegetable garden.

If you’re wondering when to transplant seedlings outside we have an article for that as well!

Pot Up Seedlings for Strong, Healthy Plants!

Person using a spoon to separate seedlings from a starter tray.

Recognizing when to pot up seedlings is an important skill that takes time to develop. With a little practice, you’ll be able to spot the signs quickly.

To get more tips and tools for planting a garden, be sure to visit the Seed Starting page on our website. There you’ll find growing guides, product recommendations, and tips to help you have the best garden yet.