Leggy Seedlings: What Causes Them and How to Fix Them

Leggy Seedlings: What Causes Them and How to Fix Them

By Michael Jenkins

Starting seeds is often the beginning of a great gardening adventure–you’ve selected the plants you want to grow, started them carefully in seed starting trays, and mindfully tended them. Gardening is a living enterprise, however, and sometimes things don’t go according to plan. Instead of healthy, growing seedlings, your baby plants may look a bit . . . off. They may have thin stems, not stand up on their own, or seem like they’re growing far too long for the size of their leaves. These are all symptoms of leggy seedlings, a problem that can arise when newly sprouted plants don’t get the right conditions to thrive. The good news is that leggy seedlings aren’t necessarily the end–there are ways to prevent them, some ways to fix them, and always lessons to learn for next time. Let’s dig in!

What Causes Leggy Seedlings?

Leggy seedlings generally occur for one of two reasons. The primary culprit in what causes leggy seedlings is a lack of light–many seedlings need “full sun” amounts of light to thrive. When there’s not enough light, the seedling goes looking for it, growing towards the nearest light source in an attempt to get what they need.

However, insufficient light isn’t the only thing that can cause leggy seedlings. Overcrowding can do it as well–seedlings competing for space will often get leggy. Soil temperatures that are too high or too low can also cause leggy seedlings, as newborn plants struggle to adjust to their conditions. Finally, inconsistent watering will occasionally cause leggy seedlings as the plants’ growth cycle is uneven and maladjusted.

For any of these causes, the result is long, weak stems, pale coloring, sections of stem that are overly narrow and don’t fully develop, and weaker roots. This can lead to plants that are prone to disease, vulnerable to pests, or just unable to grow fully. Fortunately, there are some things we can do to prevent leggy seedlings and help support plants that have grown leggy.

Preventing Leggy Seedlings

There are some relatively easy ways to prevent leggy seedlings when you’re starting seeds at home. For most home-started seeds, it all starts with light. Insufficient light is the number one cause of leggy seedlings in most cases, so ensure that your plants are getting enough light. Sadly, natural light probably won’t do it–even a south-facing window generally doesn’t get the 12-16 hours of direct sun that most vegetable seedlings need. You may need to supplement your plants’ light intake with grow lamps. The bulbs are designed to provide the full spectrum light that plants need to grow. They’re affordable, come in both incandescent and LED forms, and a couple of them in utility lamps or desk lamps can provide enough light for a tray of seedlings.

If light isn’t the issue, we turn our attention to temperature and water. Most seedlings grow best in a set series of temperature ranges, generally between 75F and 80F (23C to 27C) during the day with nighttime temperatures of 65F to 70F (18C to 21C). Checking the soil and air temperature around your seedlings throughout the day is a great way to keep track of their needs and determine if they’re being met. While you’re at it, make sure that there’s enough water–your seed starting medium should be consistently damp, but not soaked or puddling. Using a seed tray with a clear plastic cover to keep moisture in can help a good deal–just make sure to give your seedlings fresh air every now and then.

Taking these steps when starting seeds should help ensure that you avoid leggy seedlings, while giving you a guide to how to prevent them in the future. But what do you do if you have leggy seedlings despite your best efforts? There are some options.

Fixing Leggy Seedlings

So if you have leggy seedlings, what can you do to fix them? Fortunately, there are some things we can try to fix leggy seedlings. While nothing is guaranteed, you can give your leggy plants their best chance at life. You may also want to start some additional seeds, just to be sure that you’ll have healthy plants.

For leggy tomatoes, peppers, or eggplants–three common veggies that are prone to leggy-ness–the solution is to replant the seedlings and bury them up to the first set of leaves. These plants are interesting for many reasons, including their ability to grow new roots from the stem if a portion of the stem is buried. By gently repotting them this way, you’ll give them a chance to recover. Again, nothing’s guaranteed, but this is the best practice for dealing with leggy seedlings for these plants. This approach doesn’t generally work on vining plants, unfortunately. With leggy cucumbers, melons, or squash, the best approach is to give them ample light–the grow light may need to be only a few inches/10 cm from the plants–and see if they recover while starting over with new seeds grown under better conditions.

Leggy Seedlings Aren’t the End

If you’re dealing with leggy seedlings, please remember that this isn't the end. Gardening is about learning, experimentation–and making occasional mistakes. Give yourself some grace, fix what you can, start some more seeds, and take note of the lessons learned so you can prevent leggy seedlings in the future.

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