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4 Signs it is Time to Repot Your Seedlings

Updated: Mar 26

As your plants or seedlings grow, it is important to recognize the signs of when to transplant the seedlings into bigger pots. Learn to recognize the early signs before issues arise that will damage or weaken your plants. Failing to pot up seedlings will stunt their growth, cause them to become weak and unhealthy, and may even cause them to die. There are a few obvious things you can look for that will help you know when it is time to move your seedlings into bigger pots. These are early signs.

1. When Your Seedling is as Tall as the Soil is Deep

2. When Your Plant or Seedling is Drying out in Less than 24 Hours

3. When your Seedlings Have a Strong Root Base

4. When Seedlings are 3/4 to 1 Inch Tall

1. When Your Seedling is as Tall as the Soil is Deep

The number one tell-tale sign that it is time to pot up your seedlings is noticing when they become as tall in height as the soil is deep. Unless you are growing a vining plant (like peas or cucumbers) or a stalk plant (like corn, sunflowers, or onions) plants need at least as much soil depth as the plant is tall to be able to grow a large enough and strong enough root system to support and sustain the plant.

Celery seedling, seedling developing roots.  Seedling being held.  Vegetable seedling.
This celery seedling is taller than the soil is deep.

2. When Your Plant or Seedling is Drying out in Less than 24 Hours

If you are having to water your seedlings more than once a day to keep the soil moist, it is time to transplant your plants into bigger pots. Having a larger soil mass will help the soil stay moist between watering. (Note: On the other hand, if your soil takes more than 3 or 4 days to begin drying out, you probably have your seedling in too large of a container and are at higher risk of things like "damping off" (rot and disease killing the plant)

I buy almost all my seed starting containers from West Coast Seeds except for my 6 inch pots. The 6 inch pots are great for tomatoes and peppers as they mature.

3. When your Seedlings Have a Strong Root Base

If you pull your seedling up out of its current pot and notice that the roots are wound around the outside of the pot, it may be time to transplant your seedling into a bigger pot or container. If you notice your seedlings are becoming weak and leggy, here are some steps you can take to fix and avoid that.

A pepper seedling being held.  The roots of a seedling developing.  This seedling is ready to be repotted.
This pepper seedling has developed a great root system.

4. When Seedlings are 3/4 to 1 Inch Tall

If you have seeded fairly thick (as I like to do with small seeds) you can transplant them as soon as they are around 3/4 to 1 inch tall. Some people suggest waiting until the seedlings have their first two "true" leaves. these do not include the first "seed leaves" that sprout at germination. These are called cotyledons. if you wait until the true leaves start coming in, the seedling will be strong enough to better tolerate handling and transplanting.

Flower seedlings in a tray.  When to transplant seedlings.
When seedling close together, gently separate and transplant when they are almost an inch tall.

Why Not Just Start Seeds in a Bigger Pot?

You may be wondering if you can skip this whole replanting step and just start your seedlings in a bigger pot in the first place. Unfortunately, it is not that simple. Planting seedlings in a smaller pot and transplanting them as they grow is helpful for two reasons.

  1. The seedlings develop stronger roots. - The root of a plant always tries to go down as deep as it can. A small seeding in 10 inches of soil will try to send its spindly root down to the bottom of the pot, before it starts working on sending out horizontal roots. This is not the quickest way to grow strong roots, but is a plant survival technique for when there is limited water. By gradually increasing the pot size you are able to force your seedlings to develop strong horizontal roots which translates to stronger plants.

  2. Better moisture control. - As mentioned above, having a small seedling in a great big container doesn't allow the soil to dry out as often as it should and can result in a number of issues; damping off, rotting, mold, algae, poor nutrient uptake and poor oxygen uptake for the plant, even increased risk of pests like fungus gnats to name a few.

Signs that you waited too long to transplant seedlings...

As previously mentioned, it's best to know how to spot the early signs that your young plants need bigger pots. If you wait too long, more serious signs of trouble might start to show. At this point you need to work quick as your plants need a rescue before its too late! Some late signs of trouble are:

  • Leaves on the plant are starting to turn yellow. This happens starting from the very bottom leaves and progresses upwards. This is a big sign that your plant has used up all the nutrients available in its tiny cell or pot and it needs some fresh soil with new nutrients. The entire plant might also be changing from a dark green to light or pale green. The nitrogen in the soil has been depleted. Remedy this by planting into a larger size pot with fresh, quality potting soil. I do not recommend trying to feed small seedlings with any type of liquid fertilizer when in a fragile state, there is a high chance you will burn and kill them.

  • Your plant becomes "root bound". As the root system grows, it eventually fills the small pot or cell it is in. This is ok to a point, but once the roots become so heavily coiled and bound in the bottom of the pot, they produce a hard mass and begin to choke themselves out. They will no longer be able to utilize nutrients or oxygen and the plant will deteriorate.

In this case, an ounce of prevention is worth a pound of cure. When a seedling is weakened or damaged after waiting too long to transplant, it will be difficult (and take much longer) to bring it back to good health and begin to thrive again. All is not lost if you act quickly, but don't wait for visible signs of trouble, it will be more work in the long run.

Snapdragon seedlings that need to be repotted.  This photo shows when to repot seedlings.
These crowded seedlings were left too long and will be difficult to separate without breaking the roots.

Do I Need to Start Seeds Indoors?

Not all seeds need to be started indoors. There are many that do well planted directly into the garden. Find out what seeds to start indoors and what seeds to direct sow here.

If you have found this article helpful and would like to see more gardening tips and tricks for gardening in Alberta and other zone three gardening climates, please subscribe to my blog (the bottom of the home page) and follow me on Pinterest, Instagram, Facebook and/or YouTube!


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