How and Why to Up-Pot Your Seedlings
If your seedlings have outgrown their current container, up-potting them gives them room to expand. Join farmer Briana Yablonski to learn when and how to complete this process.
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Growing your own transplants provides all sorts of advantages: you can save money, grow hard-to-find varieties, and enjoy the satisfaction of watching a seed transform into a healthy plant. But did you know seed-starting involves more than placing seeds in the soil and nurturing them until they germinate?
You’ll also need to care for the seedlings until they’re ready to move to their final homes. Providing the proper light, temperature, and moisture is key, but you must also pay attention to the growing space.
When plants become rootbound, they have trouble taking up water and nutrients and suffer. Up-potting your seedlings to larger containers helps keep them healthy until they’re ready to go into the ground. If you’re unsure how or why to up-pot your seedlings, stay with me to learn the ins and outs of this process.
What Is Up-Potting?
Up-potting involves removing a plant from its container and placing it in a larger pot. You can up-pot any plant, from rapidly growing seedlings to mature citrus trees to decades-old houseplants. Gardeners sometimes refer to this process as potting up or bumping up.
Up-potting is a form of repotting, but there are other types of repotting. For example, you can remove a pot from its container, add fresh soil, and then replant it in the same pot.
Why You Should Up-Pot Your Seedlings
Simply put, you should up-pot your seedlings when they need more space to grow! The goal is to ensure a lack of space never limits the plants’ root expansion.
When roots contact the bottom of a container or cell, they grow in an unnatural circular pattern. This circle increases over time until the bottom of the pot contains a dense mat of fibrous roots. At this point, the baby plants have difficulties taking up water and nutrients, so they often become discolored, stunted, and weak.
Crowded roots are a sure sign you need to up-pot your seedlings. However, you can also look for symptoms like stunted growth, yellowing leaves, and wilting even when the soil is moist.
When and How to Up-Pot Seedlings
Now that you know why you should up-pot your seedlings, let’s dive into a few instances of when and how to complete this process.
Open Flats
Sometimes, starting seeds in open flats or large containers makes the most sense. Packing lots of seeds into a large tray works well if you have limited indoor space for seed-starting or need to place seeds like tomatoes and peppers on heat mats. If you sowed 32 tomato or pepper seeds in 4-cell trays, the trays would take up the space of a standard 10×20 tray. However, you could also fit the same amount of seeds in a six-inch by six-inch container!
This method also makes sense when sowing seeds with unknown or poor germination rates. For example, if you’re planting seeds that are a few years old and are unsure how many will germinate, sprinkle them in an open flat or pot rather than planting them in trays and risking empty cells.
How and Why to Up-Pot
Of course, these baby plants will become crowded a few weeks after they sprout. Tightly spaced seedlings will compete for water and nutrients. This spacing also leads to decreased airflow between plants and an increased likelihood that they will develop diseases. That’s where up-potting comes in.
- Look for true leaves. Once they have developed at least one set of true leaves, you can move them to larger containers.
- Remove them. Start by gently removing all the seedlings and the soil they’re growing in from their container. Even if the plants are small, their sheer number will create a sizable root mass that holds the soil together. If the soil crumbles as you try to remove it from the container, you can wait another week or two to upgrade the container size.
- Separate them. Gently tease apart the roots by holding them by the cotyledons, the first set of leaves to emerge from a seed. Since these leaves naturally fall off the plant, damaging them is better than mangling a stem or true leaf. However, you should still treat them gently.
- Prepare your containers. Fill the end cell trays or containers about a third of the way with a well-draining potting mix.
- Add the baby plants to the containers. Place one seedling in each cell or container. Hold the seedling in place and gently add more soil until the cell is full. Ensure the plant’s growth point—the area where new leaves form—is above the soil surface. Repeat this for the remaining plants, and then water well.
Cell Trays
Even if you started your seeds in cell trays, you may still need to up-pot them to larger containers. Maybe you planted seeds in 128 or 200-cell trays to save space in your heated germination space. Or perhaps you got caught up in the excitement of spring gardens and started your seeds a few weeks too early, leading to root-bound plants.
Rather than letting the plants get more crowded in their trays, you can up-pot them to larger cells or containers.
How and Why to Pot-Up
Up-potting plants that have outgrown their current cells allows them to remain healthy until they are ready to be planted in the ground. This will not only keep them healthy as they wait in their containers, but it will also decrease stress during the transplanting process.
- Look for crowded roots: I recommend up-potting seedlings in cell trays when you notice the roots starting to cluster along the bottom of the cell. While it’s okay for the roots to grow the length of the entire cell or container, there should still be room for them to expand.
- Determine which size containers to use. After you decide to move the plants to larger containers, determine which size will work best. First, consider the plants’ growth rate and how long they will continue growing indoors before you plan to transplant them outside. Next, ensure you have a large enough heated and lighted space to house the larger containers.
If your fast-growing tomatoes are growing in 72-cell trays and you plan to plant them in two weeks, you can move them to three-inch pots. However, if they’ll be sitting inside for another month, choose a deeper, four-inch pot.
- Add potting soil: Fill the large cell trays or containers with a small amount of potting soil, ensuring there is enough free space to fit the smaller plugs.
- Transfer the young plants: Remove a plug from the tray, gently loosen any tangled roots near the bottom, and add the plant to the new container. Fill the remaining empty space with potting mix and water well.
Tips and Tricks
Moving tiny seedlings from one container to another can be intimidating, especially if it’s your first time. These tips will help simplify the process and ease your worries.
Expect Wilted Plants
Don’t be alarmed if your seedlings look sad after you up-pot them from one container to another, especially if they’re going from a crowded open container to an individual pot. Handling the plants’ roots naturally stresses the plants, so droopy leaves aren’t a major concern. If you place the freshly up-potted plants in an area between 70-80°F (21-27°C) and keep the soil moist, they will bounce back within a few days.
Avoid Planting Too Deep
Some beginner gardeners make the mistake of planting too deep when they up-pot. When transferring seedlings from one container to another, aim to keep the soil line in the same place. Burying the stems or growth points can lead to rot and slowed growth.
However, you can plant some species deeper. Plants like tomatoes, peppers, and basil will develop roots where their stems contact the soil. Therefore, you can plant the majority of their stems underground without worrying about rot. Just make sure to leave at least the top set of leaves above the soil.
Provide a Steady Environment
When new growers spot wilted leaves after repotting, they sometimes try to love their plants a little too much. Rather than constantly watering your plant, adjusting the temperature, or moving it under brighter lights, keep the environment steady.
The ideal temperatures depend on the type of plant, but most vegetables prefer air between 65-80°F (18-27°C). Ensure they receive ten to twelve hours of bright light each day, along with dark nights.
