Potting Up: Why Your Seedlings Need a Bigger Space

We do a lot of “potting up” here at Sow Right Seeds. Potting up is a simple process to give your little seedlings more room to grow healthy roots before planting them outdoors. We’ll show you how easy it is to do and why it’s an important step in growing plants from seed.

Potting up is the process of transplanting young seedlings from their original seed-starting trays or cells into larger containers. This is typically done when the plants have outgrown their current containers. By moving the seedlings into bigger pots, their roots will have more room to grow, and you’ll have healthier plants for transplanting outdoors.

It's time to plant up whenever a seedling has outgrown its current container. At a minimum, seedlings should have at least two sets of true leaves. There are several stages of growth that are natural times to pot up seedlings.

• Once the seeds have germinated and have two sets of true leaves, it is time for fertilizer and less heat. So this can be a good time to pot up.

• Potting up can also be done around the time that you start hardening off the plants. In my experience, the plants will dry out too quickly if they are in too small of a container. So, it can be worth potting up before the transition.

• Bigger roots will take up more water. If you notice the pots are drying out too quickly, it’s time for potting up.

• Have leggy seedlings? This can be at the right time to pot up and plant the stem deeper.

Some plants grow slowly and don’t need to be potted up before they go outside. However, some plants quickly outgrow their small starting trays and need more room to develop a strong root system.

Potting up allows you to plant stems deeper on varieties that benefit from this. Tomato seedlings are one of these. They will develop roots along the stem that is planted deeper into the soil.

Sometimes, I don’t plan on potting up, but the weather forces me to. If the seedlings have outgrown their container and it’s still not time to plant them outside, I will pot them up.

Potting up will prevent the seedlings from becoming root-bound. For many plants, once their roots become bound up in the confines of their container, they quit growing branches and leaves.

Potting up seedlings from their seed starting medium is an excellent time to put them in nutrient-rich soil. You’ll soon notice how their growth really takes off.

One of the benefits of starting seeds indoors and potting up is you can start more seeds in a small amount of space. Seeds don’t need much to get started, but they may need supplemental heat. It’s easier to heat smaller containers, especially when using heat mats.

Select pots that are larger than the seedling's current containers. Ensure the new pots have drainage holes at the bottom to prevent waterlogging.

Use a high-quality potting mix. You can also mix in some compost or fertilizer for added nutrients.

Before changing pots, water the seedlings in their original containers. This helps loosen the soil and reduces transplant shock.

Gently remove the seedlings from their original containers, being careful not to damage the roots. If the seedlings are root-bound (with roots circling the bottom of the container), gently tease the roots apart to encourage outward growth. (If the plant is okay with this.)

Place each seedling in the center of its new pot at the same depth it was growing in the original container. Fill in around the seedling with the prepared potting mix, gently firming it around the base of the plant. Plant tomatoes and eggplants deeper.

After potting up, water the seedlings thoroughly to help settle the soil and encourage root establishment. Ensure that excess water can drain freely from the bottom of the pots.

Place the newly potted seedlings in a suitable location with adequate light and temperature conditions for their specific needs. Continue to monitor and water them as needed, and gradually acclimate them to outdoor conditions if they will eventually be planted in the garden.

• You don’t want to bury peas, beans, or cucumbers any deeper than they were already growing.

• Be gentle with the plants. Some don’t like having their roots disturbed, and you don’t want to squish the stem or leaves.

• Continue watering and fertilizing. Give seedlings enough light and airflow.

• When it’s time for transplanting outdoors, harden them off first.

• Some gardeners may pot up several times. (We’re looking at you, Daryl.) If the danger of frost has not passed, you will want to keep those tomato plants protected a little longer. So, pot it up instead of putting it outside.

Potting up is often a necessary step when starting seeds indoors. When your seedlings have outgrown their space, potting up will give them more room for healthy growth. When done correctly, you’ll have robust plants with a vigorous root system, resulting in an abundant harvest.

Take a look at your seedlings and see if it’s time to be potting up!

Written by Beverly Laudie