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When And How To Transplant Seedlings Into The Garden

Raising plants from seeds can be a rewarding and exciting way to add new varieties to your garden. Many of the best and most unusual varieties of vegetables are simply not available in your local nursery and your only option is growing these plants from seeds. But in order to grow these unusual varieties, you must know something about planting seedlings.

How to Transplant Seedlings

One common question from people who are growing plants from seeds is, “How do I know when my seedlings are big enough to put out in my garden?” This is a good question to ask when learning how to start plants from seeds because planting seedlings out in the garden at the proper time is crucial to their development later on. If you put them out before they are ready, they may have a hard time surviving the elements. If you wait too long, your seedling may become pot bound in its original container.

When it comes to how to transplant seedlings, there is no hard and fast rule to how tall a plant should be before you put it out in the garden, due to the fact that different plants grow to different sizes. Also, the amount of light a seedling gets can influence how quickly a plant grows in height when you are raising plants from seeds. If there is not enough light, a plant can grow very tall very quickly, but this plant may or not be ready for planting out. The best way to judge if a plant is large enough to plant out in the garden is to look at the number of true leaves.

True Leaves on a Seedling

The general rule of thumb is that when a seedling has three to four true leaves, it’s large enough to plant out in the garden (after it has been hardened off).

When you plant a seed, the first leaves to emerge are the cotyledons. These leaves will look different from leaves that will grow later. The purpose of these leaves is to provide stored food to the seedling for a short period of time.

True leaves grow shortly after the cotyledons. The true leave emerge and start generating energy through photosynthesis that will help feed the plant for the rest of its life. Making sure that the plant has enough of these leaves to keep it sustained when planted out in your garden is important to its proper growth.

Just remember, it isn’t how tall but how many true leaves your plant has that will determine when you should be planting seedlings out. But even when your seeds are big enough to plant out, make sure you harden off your seedlings before planting them. When growing plants from seeds, you want them to be plenty prepared to grow into beautiful plants that will provide you with a bounty of delicious vegetables.

One common question from people growing plants from seeds is "how do I know when my seedlings are big enough to put out in my garden?" This is a good question to ask, and this article will help.

Why and How to Repot Seedlings

One of the problems with starting seeds indoors is that they sometimes end up outgrowing the small cell they were started in. In a healthy seedling, just about as much effort is spent toward developing strong roots as stems and leaves. So here’s why and how to repot seedlings.

Why Repot Seedlings

If you’re starting your seedlings in a cell tray with a reservoir, eventually when you lift up the cell tray to refill the reservoir, you’ll find that the roots have made their way out the drainage hole at the bottom of the cell and into the reservoir itself.

Once you find this happening, you’ll need to repot them. Why? Because it leads to two bad things:

  1. The seedling’s taproot will get bound up and tangled, making removal difficult and damage much more likely.
  2. The roots that don’t make their way down into the watering hole will wind themselves around and around the cells, resulting in the seedling being “rootbound.”

What’s a taproot?

The taproot is the longest, strongest root of a plant. It helps anchor the the seedling. Until a more extensive root system develops, the taproot is the main source of water and nutrients for the seedling. Plants with a long taproot are drought tolerant and often more easy to care for. (Here’s more about the purpose and benefits of a taproot.)

Not all plants rely significantly on a taproot to establish themselves. These plants can withstand damage to the taproot and come out the other side perfectly healthy. But they must be repotted or transplanted before the taproot begins to mature.

If a seedling’s taproot is damaged once it’s begun to mature, the seedling will have to put effort into repairing it, rather than growing taller and stronger. For some plants, if the taproot is too badly damaged, and not enough other roots have developed, the seedling may die.

What’s it mean to be rootbound?

You know how kids outgrow their shoes SO FAST? Secondary seedling roots—the roots that are additional to the taproot—act the same way. They grow really fast, and if they don’t have room to spread out or down, they’ll start circling around and around the inside of the pot.

Eventually, with nowhere for the roots to go, the seedlings will stop growing. This keeps them from getting as big and strong as they can before transplanting them.

The solution? Repot them!

How to Repot Seedlings

It can feel a little scary to uproot a seedling from its cozy little cell it was started in. So here are my tips for how to repot seedlings in a way that helps make sure they stay healthy.

  1. Wait until the plant has grown at least one set of true leaves. At this point, it is able to photosynthesize, and should be strong enough to handle the move to a larger pot.
  2. Fill the larger pot with growing medium—I like to stick with seed starting mix just to be safe.
  3. Create a hole for the transplant by digging a few inches into the soil.
  4. Remove the seedling from its cell as gently as possible, disturbing the root ball as little as possible. Turning the cell over into your hand usually works the best.
  5. Don’t remove, shake or brush the soil from the roots—the less they’re bothered, the better.
  6. If your seedling is extremely root bound, loosen some of the smaller roots on the outside of the rootball. This will encourage them to spread out in their new home.
  7. Gently set the rootball of the seedling down into the new pot. These 4″ pots are usually big enough for the seedling to live in until transplant.
  8. Lightly pack soil around the stem, making sure the roots are completely covered.
  9. Water the seedlings in their new, larger pot to help them re-establish their root systems.

Waiting for roots to re-establish

After you repot your seedling, you’ll probably notice a significant slow down in growth. Don’t worry—this is totally normal!

Whenever you transplant a seedling, even if you’re reeeeeeeally careful, the microscopic root hairs that grow out from each root are damaged. As young as the plant is, it takes a fair amount of energy to regrow them.

Check out these tiny little root hairs on this newly germinated spinach seed!

So you will likely see little to no growth happening in that first week or so after repotting. Just make sure the soil stays moist (but not completely saturated) to encourage rooting. I put my 4″ pots on old cookie sheets and fill the cookie sheet with water so they can continue to be watered from below.

As long as the seedling doesn’t appear to be dying or wilting, it will eventually start growing again.

More seed starting advice:

Handling seedlings can be scary, but these tips for how to repot seedlings can help make sure they stay healthy! Let me know if you find them helpful.

Seedlings often quickly going to outgrow the little cells they're started in, so you'll want to repot them. Here's why and how to repot seedlings.