Potting Up Seedlings

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Remember the tomatoes that were planted last month using sterile media and cut paper tubes? Well, here they are after 3 weeks of growing—note a couple of sets of true leaves. The first two leaves are called cotyledons (kädəˈlēdn), which provide initial growth for the plant and serve as an energy source.

3 Week Old Tomato Seedling

3 Week Old Tomato Seedling
Photo by Stacey Luker

We’re only into the latter part of February, about 4-6 weeks away from the earliest planting time for plants such as tomatoes. The seedlings are begging for more space to grown so we’ll re-pot them into larger containers. Once again, you don’t need anything fancy—just a clean container and a good quality potting mix (no heavy garden soil).

You can even use something as simple as an inexpensive plastic cup preferably 18 ounces that has holes that have been drilled for drainage. Containers should be thoroughly cleaned and disinfected. One option to disinfect is immersing the container for 5 minutes in a solution of 1-part bleach to 9-parts water then rinsing thoroughly.

Red Plastic Cup with Holes for Drainage

Red Plastic Cup with Holes for Drainage Photo by Stacey Luker

When the container is clean and able to drain, make sure the seedling has been lightly watered. The larger container should be filled about half full with potting mix. If the seedlings are in cardboard tubes, cut away the tube. Otherwise, hold the container upside down supporting the seedling between two fingers. Tap the bottom of the container and/or gently squeeze the sides to loosen the media and seedling. Do not tug on the plant or try to pull it out from the container as this will injure the new roots.

Removing Seedling from Container

Removing Seedling from Container
Photo by Stacey Luker

Now you are ready to place the seedling along with any attached media into the new container. Make sure to fill the container to the desired planting depth with more potting mix and thoroughly water. Note, for tomatoes you may plant up to the first set of true leaves.

Tomato Seedling in Red Cup

Tomato Seedling in Red Cup
Photo By Stacey Luker

Time now to place the up-potted seedling where it will receive 12-14 hours of light daily. The plants will be ready for hardening off and transplanting into the garden when all danger of frost has passed. Some plants such as herbs, flowers, and peppers should not need to be re-potted before setting out. However, tomatoes grow very fast under the right conditions so they may need a second repotting if it is too early to plant in the garden.

Next month, we’ll discuss the steps for hardening off the plants and preparing the garden for planting.

Written by Stacey Luker, Master Gardener Volunteer