Potting Up Seedlings: What, Why, When and How


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If you start your seeds indoors or buy small transplants from the nursery you will likely be potting up seedlings before they can be moved to the garden. If you are new to gardening or even new to seed starting let’s discuss the what, why, when, and how of potting up seedlings.

What is potting up?

Potting up seedlings is simply the process of moving your plant or seedlings to a bigger pot when they have outgrown their previous pot. Usually, when you are starting plants from seed you are starting in small containers. These small containers allow the seeds to stay moist in their initial germination phase. Once your seeds have germinated you should separate them into their own larger pot to continue their growing process.

If you start your seeds in too large of a pot initially you are not setting your seeds up for success. In a large pot with a small seedling, you will have excess soil. The excess soil will hold the water around the plant’s roots. depriving them of air and killing them. Give the plants a pot that is about an inch wider than the root ball. This will allow the roots to continue to grow and allow for better water distribution.

Many broccoli seedlings ready to be potted up into a larger pot
These broccoli seedlings have been started with 2 seeds per cell. These seedlings are ready to be potted up into 3-inch pots.

Why you should be potting up seedlings

Too many seedlings in one cell

One common reason you should pot up your seedlings is if you started too many seeds in one container. Most people starting seeds will put multiple seeds in one seed cell. I do this because not all seeds will germinate. If I only plant one seed per cell I may not get as many plants as I need for my garden due to germination rate. When potting up seedlings you can separate the multiple seedlings into their container to allow them more room as they grow.

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Root Bound

Another reason to pot up your seedlings is so the plant’s roots don’t get root-bound. As the roots of the plant continue to grow, they will take up the entire container if you do not continue to move them to a larger pot. The roots will continue to fill the pot so there is not enough room for soil, water, or nutrients. If you have a house plant that doesn’t seem to be growing or seems to be having issues you might want to consider potting it up into a larger container. Moving seedlings up to a larger pot allows them to have the space needed for their roots to continue to grow and become a strong support system for your plants.

Growing Season

If you have a short growing season and start your seeds indoors to get a head start on growing you will be potting up seedlings. I typically pot up my tomato plants 2 times before they can be grown outside in my zone. I start my seedlings in a 1-inch by 1-inch soil block to start. When they have their first set of true leaves then they are potted up to a 3-inch pot. If it is still too cold for the plants to go outside in my zone I plant up to a 6-inch pot.

Needing Nutrients

Typically when you start seeds indoors you are using a seed-starting soil mix. The seed-starting soil mix doesn’t contain any nutrients for your plants. When you are potting up your seedlings you should be using a potting soil mix. The potting soil mix contains more nutrients your plants need to grow. You can also start fertilizing seedlings once they are potted up into a larger pot.

When to pot up seedlings

When to pot up seedlings depends a lot on what type of plant is growing. If you are potting up after starting your seeds in seed trays or plugs the timing may depend on the plant. Typically you will wait until your plant has its first set of true leaves. The first leaves that develop from seed are called the cotyledon leaves. These are not the first set of true leaves. The true leaves will develop after the cotyledon leaves on the plant.

Pepper plants with true leaves forming. Ready to be potted up into a larger pot
These pepper seedlings have their true leaves growing in the center of the plant. The larger leaves are their cotyledon leaves. These pepper seedlings are almost big enough to be potted up.

Another way to tell when it is time to pot up your seedlings is if you are starting to see the plant roots either growing out the top or bottom of your plant. If the roots have nowhere else to grow they will start coming to the top or bottom of the soil. Potting up your seedlings is important if the roots have no more space to grow. Pick a larger container that is about an inch bigger than the root ball.

You may need to pot up your seedlings several times before they can be moved to the garden depending on your zone. Don’t be tempted to jump to a very large pot right away. Take the time and care to give your seedlings the best-growing conditions you can.

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How to pot up seedlings

Potting up seedlings is a very easy process. Make sure to have the larger container ready. Some plants don’t mind if their roots are disturbed when transplanting or potting up. Others don’t like their roots disturbed so just work carefully as you transfer your seedlings.

  1. Prepare your potting soil by adding some water to it. The potting soil should not be sopping wet but it should also not be dry. You should be able to make a ball out of your soil without it easily falling apart in your hand.
  2. Put a little bit of new potting soil into the new container
  3. Make sure there is enough room to fit the plant roots into the new pot.
  4. Carefully remove your seedling from the old container. You can tip the plant on its side but make sure to hold the stem between your fingers as you wiggle the plant free. Be very careful with the plant’s stem, you can also hold the plant gently by its leaves when replanting.
  5. If you have multiple seedlings per cell, carefully separate them apart so their roots are not growing together. Plant them in separate new containers.
  6. Place your seeding along with the old soil around its roots into the new container.
  7. Push down slightly so the plant is sunk in your container. This is the time when you can fix leggy plants. Bury the stem deeper in the planting hole and fill it with soil. Don’t cover any leaves with soil as this will cause the plant to die.
  8. Add additional potting soil around your plant covering the old roots and filling in the available space in the container with soil.
  9. Press down lightly on the soil to help remove any air pockets. The air pockets could cause the roots to die. Add additional soil if there is room once pressing down on the soil.
  10. Water your plant. Water seedlings from the bottom of the pot if possible.
  11. Label each container. It is easy to think you will remember what each plant is but they can easily be mixed up when you have many varieties of each type of plant.
Tomato Seedlings that have been potted up into a larger container
Tomato seedlings that have been potted up into 3 inch pots

Care for your seedlings until they are ready to be planted outside in the garden. Check to see if your plants need to be potted up a second or third time before moving to the garden to plant. You will need to harden off your plants before they are ready to be planted if you have been growing them indoors in a warm location.

Potting up is an easy way to ensure your plants have the space they need to grow successfully. What are you growing in your garden this year that you can start from seed?

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