You work hard in late winter to start seedlings for your garden. The last thing you want to do is harm your seedlings by transplanting them at the wrong time.
Knowing when to transplant seedlings is important. There are many factors that affect timing, including seedling growth, temperature, and soil.
In this post, I’ll go over some tips on determining the best time to transplant seedlings. Let’s dive in!
Signs Your Seedlings Are Ready for Transplant
True Leaves Present
The first way to know it’s time to transplant seedlings is by looking at the leaves.
When seedlings germinate, they grow a first set of leaves called cotyledons, or seed leaves.
While seed leaves are a sign of healthy growth to come, they aren’t considered true leaves.
Seed leaves are simple in shape and small in size. They’ll always be located below the true leaves. They may even have the shell of the seed temporarily hanging on!
True leaves will be more reflective of the leaf shape you see on an adult plant.
Take a look at your seedlings. Do they have one or two strong sets of true leaves? This is a good sign it’s time to start the transplanting process.
If you have houseplants, you may be familiar with yellowing leaves on plants. This is always a great indication that your plant needs a larger pot to grow in.
This same principle can apply to fast-growing seedlings. Yellowing leaves should always be a call to action. The key is to figure out whether this means it’s time to transplant seedlings.
Yellowing leaves can mean that your seedlings are not getting the nutrition they need. Perhaps the crowded roots are not able to absorb a proper amount of nutrients.
Yellowing leaves can also be a sign of too little light or too much water.
Inspect the roots and soil to determine the likely cause. If you suspect a lack of nutrients, you can apply a very diluted amount of liquid fertilizer to your seedlings.
Beginning to transplant seedlings outdoors with this symptom can give them the light and nutrition they need.
How else can you tell when to transplant seedlings? Take a look at the roots. Seedlings that have outgrown their containers will have roots coming out of the drainage holes on the bottom.
It may also look like the seedling is root-bound. This means all the roots have formed a tightly wound ball within the seedling pot.
You may experience this early on while growing your seedlings. In the case that you’re still experiencing heavy frosts, you can move your seedlings to a larger pot. This will allow their roots to spread and continue healthy growth.
Maybe you’ve already potted up your seedlings, and they’re outgrowing that container. In that case, it’s definitely time to transplant seedlings.
Too Tall for Grow Lights
Are your seedlings outgrowing your seed starting setup? Once seedlings shoot past the grow lights, it’s safe to assume it’s past time to start transplanting.
Seedlings should never get close to your grow lights. It can potentially burn the leaves and stunt their growth.
You should keep a distance of at least four to 12 inches between the lights and seedlings. The distance will depend on the brightness of the light. The brighter the light, the more space is needed.
If you can’t transplant just yet, move your seedlings to a bright window. Or, invest in a freestanding LED grow light.
When to Transplant Seedlings
Even though your seedlings are showing signs they are ready for transplanting, you may need to wait longer.
Knowing when to transplant seedlings also depends on your outdoor conditions. Let’s take a look at a few.
Danger of Frost Has Passed
For the best time to transplant seedlings, you should always plan to wait until after the last frost.
Even if warm weather makes an early surprise visit, be patient. You don’t want to move the seedlings too early only to be met with a late frost.
Here are some common last average frost dates:
- Zone 4: May 1-31
- Zone 5: March 30 – April 30
- Zone 6: March 30 – April 30
- Zone 7: March 30 – April 30
- Zone 8: February 22 – March 30
- Zone 9: January 30 – February 28
Wait until the end of your zone’s frost window. Even if it means keeping your seedlings happy indoors for a couple of extra weeks, you’ll be glad you did.
Take a look at your forecast. The weather should stay consistently above 60 degrees Fahrenheit during the day and 40 degrees Fahrenheit at night.
Soil Is Workable
You’ve waited until after the last average frost. The next thing to check is your garden soil. Is it workable?
When determining when to transplant seedlings, go out to your garden and work the soil. Grab a handful and try to crumble it. If it’s still hard, that’s a good sign that it hasn’t reached appropriate temperatures for seedlings.
Happy, healthy plants prefer pliable soil. This allows their roots to spread. It also helps them receive water and nutrients effectively.
Similar to air temperature, soil temperature should be a consistent 60 degrees. Cold soil may shock your plant and stunt its growth.
Seedlings Are Hardened Off
If you know it’s time to transplant seedlings, make sure all your seedlings have been hardened off. This is the best way to ensure your seedlings don’t suffer from transplant shock.
The process of hardening off allows your seedlings to adapt slowly to outdoor conditions.
Every day, you set the seedlings outside for increasing intervals of time. They are then brought back indoors to their seed starting station.
This process is repeated for one to three weeks.
Plant Can Handle Temperatures
All the aforementioned advice is geared toward warm-season vegetables and flowers. If you are starting cool-season vegetables, different rules may apply.
For example, lettuce, cabbage, broccoli, and Swiss chard are all cool-season vegetables. They are able to withstand cold temperatures and frosts.
You may move these seedlings out in mid to late winter, depending on your USDA hardiness zone. Most often, these vegetables thrive when temperatures remain around 40 degrees.
Planting them in late winter/early spring will extend your growing season. You will be able to transition to warm-season plants seamlessly.
Tips for Transplanting Seedlings
Once you’ve nailed down when to transplant seedlings, you can begin the process of starting your outdoor garden. Here are a few tips for transplanting.
Prepare the Soil
Every spring, it’s a good idea to prepare your garden soil.
Depending on where you live, your soil texture may be sandy, heavy clay, or loam. For sandy and heavy clay soils, you should add soil amendments in the spring.
Work well-rotted compost and manure into the top eight inches of soil. This will improve your soil texture, encourage roots to spread, and introduce healthy nutrients into the soil.
Repeat this every year, and your soil will only improve with time!
Get Plants Used to Outdoor Conditions
Getting your seedlings used to outdoor conditions is known as hardening off.
Begin by placing your seedlings outdoors for one-three hours on the first day. Every day, add an extra hour to that time. You can also transition your seedlings from partial sun to full sun during this time.
Avoid placing your seedlings outside during extremely bright or windy days at first. As you harden them off, they will build up a tolerance to both of these elements.
For more information, read our post on how to harden off seedlings.
Check the Weather
Once it’s time to transplant seedlings, check your weather app for the perfect day. Seedlings have the best chance of success when planted on dry, overcast days.
The sun beating down on your newly planted vegetables can be overwhelming for them. If you need to plant on a sunny day, try to plant seedlings in the early morning or late afternoon.
Likewise, young seedlings may not be able to withstand the force of heavy rain. While a small shower is great, avoid planting right before a big storm is in the forecast.
Let Seedlings Dry
Instead of watering seedlings right before you plant them, let the soil begin to dry out. This way, once you go to plant, the soil will easily come out of the pot.
Wet seedlings will tend to fall apart when removed from their pots. That’s not a good sight after you’ve spent many weeks fostering these plants from seed.
A slightly dry plant will slide right out when turned upside down. Just make sure to water your seedling deeply after it has been planted.
Wrapping Up When to Transplant Seedlings
Knowing when to transplant seedlings will help you start your garden successfully. By following these guidelines and tips, you’ll lose fewer seedlings to transplant shock and frost damage.
Successful seed starting can feel overwhelming. Let us guide you along the way with our Seed Starting page with links to our other blog posts and guides. We’ve highlighted the best products to use, along with growing tips and tricks.