Leggy Seedlings: How to Prevent and Fix them For Good!

Leggy seedlings vs. normal

What are leggy seedlings?

Leggy seedlings are tall, skinny, spindly seedlings that struggle to stay upright. They’re leggy because the plant isn’t getting enough light. As they stretch toward the light, they grow lanky and get top-heavy. They tend to flop over because they can’t support the weight of their leaves.

This is why giving your seedlings plenty of light from the start is important.

So, what do leggy seedlings look like?

Why are leggy seedlings bad?

When you start plants from seed you want them to grow as strong and stocky as possible.

But leggy seedlings aren’t strong enough to withstand outdoor weather conditions.

They’re also 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.

Why are my seedlings leggy?

1. A lack of strong 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 northern gardeners make growing vigorous seedlings in a window nearly impossible.

Key takeaway: A south-facing window gives off insufficient light for growing seedlings.

Seedlings need 12-18 hours of strong light per day.

And they can’t get that from a windowsill.

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 seed starting shelf plans that’ll get you up and running in no time!

2. 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.

3. High heat can cause floppy seedlings.

Heat 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.

Pro tip: Take your seedling trays off the heat mat once your seeds have sprouted.

• 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 sprout.

Related: FREE vegetable garden printables

4. 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 tender 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 small 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 2023-03-18 at 18:32

You can gently brush your hand over 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.

5. 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?

1. Give them enough light from a strong light source, like a shop light. Give them more light ASAP. The next time you start seedlings, make sure you do it under artificial lights.
2. Keep them moving, just a little. Using an oscillating fan on a timer will promote stronger, stockier growth.
3. 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.
4. 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.
5. Be vigilant. Check your seedlings every day. If they’re getting enough light but are leggy, it may be time to pot them up to a larger container because they’re crowded.