It’s Almost Time to Transplant Seedlings — What to Do for Healthier Plants This Spring

March 15, 2025 admin No Comment 5 Views

The best time to transplant seedlings is after the risk of frost has passed, usually in early spring.
Seedlings should not be transplanted unless they’ve already been hardened off. Otherwise, they’ll die.
Transplanting seedlings is easy, but keeping the soil evenly moist is key to well-established plants.

If you’ve been in the process of starting plants from seed indoors for weeks, you may be in a celebratory mood when the time comes to transplant the seedlings outdoors. But other thoughts may also occur to you, too. Was it worth all the trouble? Yes, because starting plants from seed saves money, plus certain plants simply aren’t available in flats at the local garden center.

Will my seedlings die when I set them outdoors? Well, no transplant operation is without risk, but you can minimize the risk by taking the proper steps.

Learn the right time to transplant seedlings, as well as how to perform the operation just right.

When to Transplant Seedlings Into the Ground

Transplant seedlings outdoors six to eight weeks after you sowed the seed indoors, based on the following criteria:

The last frost date for your region has passed (for warm-season plants).
The seedling has at least three or four true leaves.
The seedling has been hardened off.

True Leaves vs. Cotyledons

When the seedlings of plants such as sunflowers, pumpkins, etc. first emerge from the soil, you’ll soon see them unfurl a pair of leaf-like structures. But these modified leaves are merely cotyledons (“seed leaves”). The first true leaves will form soon after.

You should follow those three rules for most of the plants that you are likely to grow from seed. However, there are exceptions regarding the frost-date rule:

Some plants are very cold-hardy: These are the so-called “cool-season plants.”
Transplant cool-season seedlings earlier: Cool-season plants actually need to be planted earlier than warm-season plants. They don’t like the warm weather and won’t perform well if planted too late. Transplant them outdoors several weeks before the last frost date.
Examples: Great examples of cool-season plants come from the mustard family, such as cabbage and broccoli.

How to Tell if a Seedling Is Ready for Transplanting

There are really two different times that a seedling is “ready for transplanting” (meaning you will be transplanting twice). The first is signaled by the appearance of the seedling, itself. Look for the formation of the first true leaves. Their shape is different from that of the cotyledons.

When there are three or four true leaves, transplant the seedling from its seedling tray into a 3-inch pot filled with potting soil. Doing so will give the roots more room in which to grow, and a healthy root system will give the seedling a good chance for success once it is planted in the ground.

Note that plant size is not a good indicator of when a seedling is ready for transplanting. A spindly plant with just two true leaves may be taller than a more compact plant with four true leaves. But it is the latter seedling that is ready to be potted up.

The second time that a seedling is “ready for transplanting” comes after it has been hardened off, and once you can be relatively certain that there won’t be any more frosts. At this point, transplant the seedling from the pot into the ground.

Hardening Off Seedlings

“Hardening off” is a term used for the process of gradually acclimating seedlings started indoors to outdoor conditions. Seedlings not hardened off frequently die from transplant shock, which occurs because the seedling is suddenly subjected to environmental changes outdoors for which it has not been prepared.

The seedling has grown accustomed to a certain temperature and to a certain amount of sunlight indoors; hardening off provides it with a transitional period, in which it can adjust to the new conditions of the outdoors gradually.

Here’s how to harden off a potted, warm-season seedling:

Wait until the temperature consistently reaches 50°F daily.
Place it in a shaded, sheltered location outdoors during the day, bringing it indoors at night.
For a week or two, each day, gradually increase the amount of time it spends outdoors.
During this period, gradually expose it to more and more direct sunlight.
When nighttime temperatures consistently stay above 50°F, begin leaving the seedling outdoors at night. But if there’s a danger of frost, make sure to cover it.

How to Transplant Seedlings

At the end of the hardening off period, the seedling is ready to be transplanted into the soil. Here’s how to do it:

Choose a suitable site: Locate sun-loving plants in a spot that receives full sun. Find a shaded area for shade-loving plants.
Dig the hole: Dig a hole that’s slightly wider than the seedling’s root ball. The depth should be the same as the pot’s.
Remove the seedling from its pot: Squeeze the pot to loosen the potting soil. Using a butter knife, separate the soil from the inside edge of the pot. Place the pot on its side and coax the seedling out, retaining as much of the root ball as possible.
Plant the seedling: Place the seedling in the hole. Backfill with a mix of compost and soil. Gently tamp down the backfill.
Water: With a watering can, water to help the soil settle. Going forward, water to keep the soil evenly moist.

FAQ

No height can be provided as a general guideline, since different types of plants have different growth patterns. Focus on the other criteria provided here to determine the right time for transplanting.

It depends on the tray. Some trays are composed of multiple “cells” (cups meant to hold seedlings individually). Cell sizes vary; the greater the size, the longer the seedlings can stay in the tray.

A seedling should have at least 3 or 4 true leaves before you transplant it.

Warm-season seedlings transplanted outdoors before the last frost date, or without at least 3 true leaves, or without having been hardened off, are likely to die.