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How to Prevent and Fix Leggy Seedlings For Good
Inside: How to prevent and fix weak, spindly seedlings for good.
A couple of weeks after starting your seeds indoors, your shoulders sag as you look at your seedlings.
They don’t look right.
They’re thin, pale, wispy things – all skinny stems, and hardly any leaves. It feels like a seed-starting disaster!
And you wonder, “can I salvage these seedlings?”
The good news is it’s possible to fix leggy seedlings!
I’ve saved many.
And most led long healthy lives!
Why are leggy seedlings bad?
They aren’t strong enough to withstand outdoor weather conditions.
They’ll also be more susceptible to pests and diseases, and may not produce well. So, it’s vital to prevent legginess.
Before we discuss how to fix your seedlings, let’s talk about why you have leggy plants, and how to prevent this common seed starting problem.
What causes leggy seedlings?
A lack of light will cause leggy plant growth
When your seedlings don’t have enough light, they extend upwards to get as much light as possible.
As they use up all their energy to reach what light there is, they get stretched out, and you end up with frail, spindly seedlings.
A common mistake many new gardeners make is starting seeds in a south-facing window.
The weak sun in late winter and short days for norther gardeners make growing vigorous seedlings in a window nearly impossible.
Seedlings need 12-18 hours of strong light per day.
And they can’t get that from a windowsill.
“Just because a window seems bright from sunup to sundown does not mean it yields enough direct sunlight to grow plants.” —The Spruce
The best way to give your seedlings the light they need is to grow them under supplemental lights.
Setting up a seedling grow light stand is easy.
Check out my no-carpentry-required grow light stand tutorial. I’ve included a full list of supplies and instructions.
And as a bonus, you can download a free set of plans that’ll get you up and running in no time!
If you’re already growing your seedlings under lights, and they’ve gotten leggy, make sure to put the lights as close to your plants as possible without burning them.
If you’re using fluorescent shop lights, and your seedlings are stretching, it’s possible that your bulbs are too old and not putting out enough light. It’s best to replace your fluorescent light bulbs every few years.
Crowding can cause spindly seedlings
When seedlings grow too close together, they don’t get enough light, because they shade each other out.
This forces them to grow taller to compete for the light, and they end up getting leggy.
You can prevent this by thinning out your seedlings when the first leaves appear.
If they’re already in individual pots or cells and they get crowded before they’re ready to pot up, plan to use larger containers next time to keep them farther apart from the start.
Pro tip: Take your seedling trays off the heat mat once your seeds have sprouted.
High heat can cause floppy seedlings
Heating mats are a great way to germinate seeds quickly but don’t use them after your seeds have germinated unless you’re growing your seedlings in a cold room.
Some seeds require high temperatures to germinate well.
But many seedlings will have a rapid growth spurt and get leggy when they’re kept too warm.
So, germinate your seeds at the temperature range recommended on the packet, and then take your seedling trays off the heat mat once your seeds have sprouted.
Lack of air movement can contribute to legginess
Seeds that germinate outside get the benefit of being strengthened by the wind.
As the wind blows them around, they get a little workout and grow stronger so they can withstand the wind without breaking.
But seedlings grown indoors don’t get that benefit.
So, how can you create wind for your seedlings?
Use an oscillating fan.
Think of a fan as strength training for your seedlings!
It mimics the windy conditions they’ll face outside. And gives you strong seedlings.
A fan will also help keep the surface of your soil drier, which helps cut down on things like damping off and mold growth.
I use a fan clamped to a metal shelf opposite my seed starting setup. You can check out my seed starting rack, and get free plans to set up your own (no carpentry required).
Prices last updated on 2022-05-17 at 19:38
You can also brush your seedlings several times a day to strengthen them, but I’ve found that using a fan is just as effective, and more convenient if you’re not home all day.
Dry soil can cause legginess
If you let your seed starting mix dry out too much when your seedlings are young, it can cause them to get leggy.
Dry soil stops the plants from getting the nutrients they need to grow well.
Keep your soil evenly moist until your seedlings get their first leaves and are growing strong.
At that point, it’s fine to let the soil dry out in between waterings, as long as your seedlings don’t wilt dramatically. This can help harden them off and lessen transplant shock when it’s time to plant them.
But when they’re young, keep the soil moist.
How do you prevent leggy seedlings?
- Give them enough light from a strong light source, like a shop light. The next time you start seedlings, make sure you do it under artificial lights with ventilation.
- Keep them moving. A good light stand setup equipped with an oscillating fan will promote stronger growth.
- Don’t overheat them. If you’re using a heat mat to germinate your seeds, move your trays off the heat once most of the seeds have sprouted.
- Water properly. How often you should water your seedlings depends on how fast they dry out. Keep the soil evenly moist until they get their first set of true leaves.
- Be vigilant. Check your seedlings every day. If they’re getting enough light but are leggy, it’s time to pot them up to a larger container because they’re crowded.
Can you fix your leggy seedlings?
Should you scrap this batch of seedlings and start over, or try to rescue them? It depends.
Here are a few things to consider when deciding if you should try to save them:
- Are these seeds the only ones you have? If so, it makes sense to try to salvage them.
- Where are you in the season? If it’s late in the season, and you don’t have more time to start seeds, you’ll miss your planting window. So, it makes sense to try to save them.
- How leggy are they? If you’ve caught it early enough, you might be able to save them.
At what point are seedlings beyond saving?
Sometimes it’s heartbreaking, but it’s better to cut your losses.
Here’s what to look for when deciding if a seedling is too leggy to save:
- They’re limp and falling over. It’s better to start over if they’ve gotten this leggy and weak.
- The distance between the soil and the first set of leaves is more than one or two inches.
- The distance between the sets of leaves is an inch or more.
If it’s early enough in the season, and you’re not sure if you can save your seedlings, it’s best to replant.
How to fix leggy seedlings
- Make sure they’re getting enough hours of light. If you don’t have a seed starting rack, consider building one. I have plans for a DIY grow light stand that can be put together in a few hours. If you have a cold frame, consider moving your seedlings to it. You may need to shade them for a few days as they acclimate to the extra light in the cold frame.
- If they’re not getting enough light, thin them out. You should have only one plant per cell or pot. If you’ve grown seedlings in a flat, and they’ve gotten leggy, transplant them to new containers that keep them farther apart.
- Plant them deeper. You can successfully do this with tomatoes, eggplant, peppers, and basil. These plants are all able to grow new roots along their stems. Bury them in a new pot up to their first set of leaves.
- Keep the air moving around your plants. Put a fan next to your seedlings. Set it on a timer, so they get air movement for a few hours each day. Or, brush the tops of your plants several times per day.
- You can pinch back some seedlings to promote bushier growth.
Some seedlings respond well to pinching off the top set of true leaves. This will force them to branch out and grow bushier.
Do pinch annuals such as coleus, cosmos, impatiens, scented geraniums, marigolds, salvia, snapdragons, petunias, and zinnias. Herbs like basil, tarragon, thyme, and sage also respond well to pinching.
But do not pinch campanula, cockscomb, delphinium, dill, stock, larkspur, and most sunflowers.
Download Your Free DIY Grow Light Plans
Make sure you have everything you need to set up your seed starting shelves so you can grow healthy seedlings this year and every year!
Here’s a sneak peek of your plans:
Want to Learn More About Seed Starting?
Did you learn anything new about preventing leggy seedlings? Let me know in a comment below!