When to Transplant Seedlings: Expert Tips for Success

Ever wondered why some gardeners are so good at transplanting seedlings? Timing is the key! Figuring out when to transplant seedlings outside into the garden or into a larger container can change everything. With this information, you can avoid stress, promote healthy roots, and grow bigger plants for a beautiful garden.

Are you ready to learn how to time your transplanting right? Let's get started!

Increasing Garden Yields

I’m always looking for effective ways to grow more food in less space. This starts with good garden planning and good timing whether you are seed starting indoors, winter sowing, directly sowing in the garden, or transplanting seedlings.

When I first started gardening, I made a big mistake over and over: I transplanted seedlings into larger containers too soon. I want to save you from making the same mistake!

When I learned how to identify the right time for transplanting, it blew my mind. Now, I have healthier, happier seedlings, way less loss, and I am further along in my garden than when I had transplanted at the wrong time.

Benefits of Properly Timing Transplanting

We all know you need to transplant seedlings once they outgrow their original seed starting container. But does the timing really matter?

Yes! Improperly timed transplanting can lead to stunted plants that fail to thrive and sometimes dead plants, ultimately costing you time, money, and potentially, your plant’s health.

Transplanting in the right window of time reduces stress and shock and ensures a well-developed, healthy root system. That’s why properly timed transplanting can boost yields.

When Are Seedlings Ready for Transplanting

Seedlings grow fast, so how do you know when to transplant seedlings or up-pot them into larger containers? Some people transplant seedlings at the first sign of roots growing out of the bottom of the cell, and others think it is time to transplant when they see the first set of true leaves. 

Transplanting When the First True Leaves Have Formed

The first leaves from the sprouts are called "cotyledons" or seedling leaves. These are the leaves waiting inside each seed. The second group of leaves to show are called the "true" leaves. (They look like a miniature version of the leaves you'll expect to see once the plant is fully grown.) 

The true leaves supply vital nutrients for plant growth to the seedling through photosynthesis. I used to think seedlings were ready to transplant once the true leaves had formed, but that often resulted in transplanting underdeveloped seedlings that weren’t ready!

Think of your seedlings like a hermit crab. Hermit crabs only shed their shell when needed because they have outgrown it.

The shell size they need has more to do with what is inside the shell than what is visible outside. Similarly, transplant timing is not so much about when the visible plant looks ready as when the root plug is developed and ready.

Transplanting Based On Visible Roots

It is a common misconception that when plant roots grow out of the bottom of your seed starting cells, it’s time to transplant. The trouble with this is that soil types and watering practices can encourage roots to grow down to the bottom of the cells quickly before sufficient seedling root development occurs.

We practice bottom watering our seedlings so the roots naturally grow down to find the water. They can quickly grow through the drain holes at the bottom, but that doesn’t mean they are ready to transplant.

The cabbage seedlings in the photos above have roots growing out of the bottom of the cell, but there is no way that these itty bitty seedlings are ready to be transplanted!

Transplanting Based On Overall Plant Growth

While visible roots and true leaves are helpful indicators, they don’t tell the whole story! Instead, consider the overall growth to determine whether the plant is ready.

When my seedlings are approaching the time for transplanting, I choose one seedling (an average representation of that batch of seedlings) and pull it out of the cell to assess it. Here is what I am looking for:

• Root Development - When you pull a seedling out of the starting cell, the roots should come out in the cell's shape and hold that shape. If the root plug breaks away and crumbles, there is not enough root development to hold the plug in place and the seedling hasn’t been in that container long enough. If the plug is all roots or rootbound, it has already been in that container too long.

• Root Health - The roots should look nice and white, not brown and not coiled tightly.

• Support Aerial Roots - Does the plant have support aerial roots? These form once the root system is developed below the soil level and can’t develop much more. Then, the plant starts to support itself with some roots up above. Looking for the formation of support aerial roots is critical to knowing when your plant is ready!

I may sacrifice a few seedlings to assess the perfect timing, so I always plant extra. If a seedling is not ready, don’t force it!

Some years, I transplant peppers in 5 to 6 weeks. The next year, I might transplant them in 7 to 8 weeks. Each year is a little different.

Calculating When to Transplant Seedlings Outdoors

If you time your seed starting well, the weather forecast will hopefully be perfect for transplanting seedlings into the garden once they’re ready. Harden off the seedlings and transplant them into the garden after the last local frost date and within the plant’s germination temperature range.

But nature doesn’t always cooperate with our plans. If you know your seedlings are ready, but the temperatures outside aren't cooperating for moving them into garden beds, transplant them from their cells to bigger containers. 

This will give you a time buffer before full transplanting. Avoid letting the ready-to-transplant seedlings outgrow their cells! 

How to Transplant Seedlings

A few hours before you start planting, water the seedlings and fertilize and water the garden space you will be planting in. The soil moisture should be enough that the soil holds together when squeezed but also falls apart easily afterward.

Use a dibbler or transplanting trowel to make holes where you want to plant each seedling. Gently remove each seedling from its container, taking care not to damage the root system, and plant a single seedling in each hole. Gently tamp the soil down to remove air pockets.

Pro-Tip: Make sure you plant seedlings at the same depth as they were in the starting container. The only exception is tomatoes!

For more information, follow the step-by-step instructions in this guide to learn how to transplant seedlings correctly.

When to Transplant House Plants

Knowing when to transplant your house plants differs from knowing when to transplant seedlings. If you want information about transplanting house plants, watch this video about how to tell when it’s time to transplant house plants. The information about house plants starts at 2:10 in the video.