Potting Up Seedlings: A Complete Guide for Gardeners
After starting seeds indoors, they eventually get larger, and the time for potting up seedlings arrives.
Starting seeds at home is one of the best ways to get the garden of your dreams. After your seeds sprout and start growing, the time for potting up seedlings will arrive, which means it’s time to move the seedlings up to the next size pot.
Potting up seedlings is an important step when starting seeds indoors. If you use small seed trays, the pots leave little room for the root systems to grow and expand.
You want your seedlings as healthy and large as possible when transplanting them outside. I used to avoid this step, but once I realized how beneficial it is for the plants, I began implementing it in my garden and saw benefits that year.
Let’s look at what you need to know about potting up seedlings in your garden.
Related: How to Germinate Seeds Quickly in 6 Steps
What is Potting Up Seedlings?
The term “potting up seedlings” is exactly what it sounds like – you are transplanting seedlings “up” into a larger container than they had previously.
The task takes time and effort, which is one reason I tend to drag my feet to get it done. It’s not difficult, but it is a bit tedious, especially when you grow hundreds of seedlings as I do. Since some plants may need to be potted up several times, I try to save myself time by starting seeds in larger containers from the beginning. That reduces how often I need to do so and the urgency to do so.
Potting up doesn’t always refer to seedlings.
If you love houseplants as I do, potting up may refer to putting your plant into a large pot. This must be done every so often to encourage more growth in your plant.
Do Seedlings NEED to Be Repotted?
Not always. Not all seedlings have to be repotted; this is an optional step and not required for every plant.
Truthfully, you should only pot up seedlings if needed, and you should avoid repotting immature or tiny seedlings that may be vulnerable and delicate. Some seedlings live in their seed trays until it’s time to move the plants outside, but others become root-bound in their seed cells.
Typically, the larger the plant, the more likely you’ll need to pot up the seedlings. Many seedlings that start off as tiny seeds may not need repotting, such as lettuce.
Why Potting Up Seedlings Is Important
Potting up seedlings encourages your new plants to grow larger and stronger. It reduces stress and increases their strength, which is exactly what you want before putting them outside in your garden.
Here are some benefits of transferring into bigger pots.
It Prevents Plants From Getting Root-Bound
When potting up into new pots, the root systems grow without getting root-bound. The truth is that, if your plants are root-bound, they are not happy plants.
What does root-bound mean?
A root-bound plant is when the plant’s roots are restricted in the pot and start to grow in circles around themselves. I often see this in seedlings purchased from nurseries when they cannot pot up as regularly as home gardeners. The roots become tangled and unable to spread out.
Plant health is linked to root health. Plants cannot grow without strong roots that grow and spread out.
Your goal for your seedlings is to grow larger; eventually, these tomato plants or whatever vegetable plant you grow will produce food for your family. They need a healthy root system to grow larger.
If your seedlings end up with root-bound root balls, you can gently loosen them when transplanting. However, in some cases, this will harm them or delay growth a bit. I discuss this more below, but ideally, home gardeners want to prevent root binding as much as possible.
Plants Need to Be Watered Less
Another reason you move to bigger containers is that, as their roots grow larger, they dry out more quickly. Small cells with seeds yet to sprout stay moist for quite a bit, but they dry out faster with plants with large root systems.
So, moving your seedlings to newer pots with more space allows you to water deeply and stops the soil from drying out as fast.
It Feeds Your Seedlings
If you started your seedlings in seed starting mix, your seedlings are hungry. Seed starting mix doesn’t contain any sort of nutrients, so now it’s time for them to receive fertilization and more food to grow.
Potting Up Increases Airflow
Moving your small plants into larger pots will increase airflow to your plants, including their roots. Increased airflow reduces the risk of mold growth. They need air pockets in the soil for aeration, and it also helps water flow. You won’t have a strong root system without proper airflow.
When to Pot Up Seedlings
The time to pot up your seedlings varies from plant to plant. Instead, look at the factors that influence the timing for potting up seedlings, such as the type of plants you grow, the container size, and when you need to transplant your seedlings outside.
Unfortunately, you won’t find any rule or guideline that says you must up pot plants on day 25. That’s not how gardening works!
The Size Container Used
One of the first factors is the container you started the seed inside. Smaller containers, like the trays with multiple cells, require potting up sooner than if you started seeds in a larger container. Plants quickly feel cramped in tiny cells.
This is why I typically prefer to start seedlings in larger containers, such as 4-inch nursery pots. Using bigger pots means you can wait to pot up for several weeks, then transfer into 6-inch pots or 8-inch pots.
You might wonder why you couldn’t just use these larger containers from the start and avoid potting up entirely.
Well, I don’t have room for that! Those pots take up a lot of space, and I wouldn’t be able to fit all of the plants I grow on my heat mats and grow lights. If I wanted to only use larger pots, I would either need to scale up my seed starting area or reduce the number of plants I start.
Type of Plant
All plants grow at different rates, so the type of plant in the container matters as well. For example, tomato plants outgrow their containers faster than herbs. You’ll find you need to pot up tomato seedlings faster than basil seedlings.
Knowing this, consider planting in advance and starting faster-growing seedlings in larger containers than other plants. Flowers and leafy greens grow well in the six-cell trays, and pepper plants or cabbage plants grow well in 4-inch pots.
Planting Outside Timeline
Think about when your target transplant date is for each plant. Potting up won’t make a difference if you plan to put your plants outside in the next week or two. This is the time to harden off plants rather than change containers.
However, if outside planting is more than two weeks away, change the containers and give more space for those plant babies to grow up.
Watch the growth of your seedlings to determine if it’s time to move to larger pots. Does the plant look happy? Can you see roots through the bottom drainage holes?
Any roots poking through the bottom of the containers indicate that it’s time to pot up into a bigger container. This is especially true if the roots begin to spiral around themselves.
Of course, you don’t have to wait for the roots to come out the bottom. If they look too large in the container, it may be time to move up sizes.
5 Signs Your Seedlings Need to Be Potted Up
It’s a good idea to know the signs that your seedlings need out of their small pots. Moving young seedlings too early may result in stunted growth. Here are a few signs to recognize.
1. The Seedlings Have a Set of True Leaves
One of the first signs that it’s time to change pot size is that your seedlings develop one to two sets of true leaves. This often happens three weeks after sprouting. You don’t want your plants to exhibit signs of stress before you take them out of their small containers.
So, three weeks after sprouting is the best time to pot up.
2. The Cotyledons Turn Yellow & Fall Off
Cotyledons are the first set of leaves that appear from the seed after sprouting. These aren’t the true leaves; true leaves are the second and all following sets of leaves.
Cotyledon leaves fall off the young plants; this is normal to do so. However, if they do so when your seedling only has one to two sets of leaves, it’s time to transplant in their new home.
3. The True Leaves Turn Yellow
If your true leaves are yellow, then it means your plants are lacking nutrients. They need nutrients from a healthy potting mix.
4. The Roots Wind Around the Root Ball
One of the signs that it’s well past time for potting up is the roots circle around the edges of the root ball. This signifies that they don’t have enough room in their original container. The roots begin to circle the root ball and may poke out the bottom of the pot.
5. The Seedlings Become Crowded
Seedlings that are crowded or too close mean that it’s time to change pots. The young plants begin to compete for light and nutrients, crowding each other. This means your plants are ready to spread their roots and be big plants in their own pots.
How to Pot Up Seedlings: Step-by-Step
Potting up seedlings is quite easy. Here are the steps that you need to take to change pot sizes.
1. Pick Larger Containers & Labels
Start by picking new containers that are slightly larger than the ones the plants are already in. Ideally, the containers should be twice as large; this is a good goal. If you want to, it’s safe to even go up more than twice as large if you started in very tiny plant cells.
If you started in small cell trays, consider moving up to 4-inch containers. If you started in larger containers, try 6-inch pots!
Some gardeners prefer using peat pots over plastic pots. You cannot reuse peat containers, but you plant them right into the garden, avoiding any shock from taking the plants out of their containers when planting in the garden.
It’s also a good idea to ensure you have enough plant labels when moving your seedlings from their cell pack to individual containers.
Related: 7 Best Seed Trays and Pots for Starting Seeds at Home
2. Get Potting Soil & Put in the Bottom
Once you have the new pots, you need new soil as well. Instead of using a seed starting mix, pick high-quality potting soil. Potting soil is denser but contains nutrients your new seedlings need to grow larger. At this stage, it’s safe for plants to have exposure to nutrients.
The only time you don’t want to use all potting soil is if you are transferring small seedlings not as well established with thin, fragile roots and no formed root ball. Smaller seedling benefits from fluffier potting soil; consider mixing half organic potting soil and half seed starting mix.
Moisten the soil before putting a layer of soil into the bottom of the container. Gently take the plant out of the small container without pulling on the seedling itself. Put its entire soil mass and roots into the new container and fill in the sides with potting soil.
3. Deal with Root Bound Seedlings
If you have root-bound seedlings, don’t worry; you can fix this.
- Start by loosening the coiled roots. Use your hands to gently tease and pull the roots. Use scissors to trim if you have long roots that stick out of the pot.
- Spray the roots with water if they are stubborn and won’t loosen up.
- If you have a stubborn root ball that won’t untangle, make several vertical slits in the root ball to stimulate the growth of new roots.
4. Learn How Deep to Bury Seedlings
Knowing how deeply to bury seedlings is essential. If the seedlings you transfer are tall and leggy, then it’s safe to plant most seedlings deeply around the stem to give them more strength.
In many cases, it’s preferred to bury seedlings deeper when potting up seedlings. The buried main stem of tomato seedlings will shoot off new roots, which happens for other nightshade family members. It’s safe to deeply bury peppers, potatoes, and eggplant.
Other places, like brassicas plants – cabbage, kale, broccoli, cauliflower – handle a little burying, especially when they grow larger and sturdier.
However, other plants don’t like to be buried deeper in their new pots, causing the stems to rot and kill the plant.
5. Water & Fertilize Newly Potted Seedlings
After moving your seedlings, it’s time to give your plants good watering. It’s best to water from below, giving the soil time to soak up the water from the tray underneath.
It’s safe to give diluted seaweed extract fertilizer in their water to reduce the risk of transplant shock.
6. Continue to Provide Care Until Transplanting
Your new seedlings will continue to live happily and grow in their new containers until you move them out to their garden home. It’s essential to harden off indoor seedlings before transplanting outside to prevent transplant shock or death of your plant. You want sturdy seedlings when moving plants outside.
Potting up seedlings is just one thing you’ll have to do to keep healthy young plants. Keep an eye on the growth of the plants and move them when they outgrow the original container. Your seedlings will thank you!