Leggy seedlings are pretty common among veggies in the brassica family. But, that doesn’t make it any less frustrating when it happens.

To help fix your leggy brassica seedlings and strengthen them up, make sure they are getting enough sunlight, aren’t being exposed to high temperatures, and have enough room between each other.

In this article, I’ll also discuss the best way to transplant your seedlings once they’ve gone leggy so that they’ll start to grow outwards instead of just upwards. Let’s get into it!

Brassica is a plant family that includes a lot of common garden vegetables like kale, collards, broccoli, cauliflower, kohlrabi, and brussel sprouts, just to name a few.

Because all of these vegetables are related, they can all be treated in much the same way. What the solution is for one brassica veggie is likely the same for another brassica veggie.

Because of this, it can be easy to find a solution for leggy brassica seedlings because they’re all so similar to one another.

While leggy seedlings don’t automatically equal a death sentence for your brassicas, it can cause major problems if left untreated. 

Leggy seedlings are tall and skinny meaning that their stems are very weak. Any moderate weather event has the potential to snap the stems of your brassicas and leave you with sad and unsalvageable seedlings. 

You’re probably wondering why your seedlings are even leggy in the first place. Well, here are some of the most common causes of legginess among brassicas.

When young seedlings don’t have access to enough light, they try to stretch to get access to any bit of light they can. Because of this, their stems end up very long but also weak. 

This is especially common if you start your seedlings indoors. Indoor spaces get very limited sunlight, even if you have the best windows. Most brassicas need about 6 hours of sunlight per day to grow into a healthy plant.

If you like to use grow mats or heat mats to help get your seedlings started, then this might be causing legginess among your brassicas.

Young seedlings love the warmth from the heat mats, but it sometimes can send them into a frenzy and cause them to grow too quickly. 

Brassicas are also a cool season crop. If your seedlings are planted outside and the weather is already quite warm, then your brassicas are likely to go leggy and may even bolt.

When brassicas bolt, they will send up a flower head and start making seeds. This is not good because bolted brassicas tend to stop putting energy into leaf or head production and may even start to taste a little bitter. 

Check out these articles for more information on brassica head formation:

Warm temperatures make brassicas think that their season is almost over and that they must quickly reproduce before they die. This is why they start producing seeds. 

Brassica seeds that are started in plug trays can quickly outgrow their cells. If the cells are too small for your seedlings, then they can become root bound and struggle to grow strong stems, among other problems. 

Crowding can also happen in seed strip trays. These are seed trays that aren’t separated into their individual cells but instead contain multiple seedlings per row in the tray. 

If the seeds sprout too close together, then they may start competing for things like nutrients and light. And light competition will lead to legginess. 

Most likely, moving your seedlings into a better-lit area will fix any leggy problems. If your seedlings are indoors, consider transplanting them outside. 

Brassicas are cold hardy and can withstand a little bit of frost. So don’t be afraid to move them outside if temperatures are at least 40 degrees.

If temps are staying consistently below 40 and you’re worried that it might be too soon to move them outside, then consider setting up some grow lights. 

Grow lights are a great option for anyone who has limited space or doesn’t have access to a well-lit, indoor growing area like a greenhouse or a home with lots of windows. 

For seedlings that were directly seeded in the garden and appear leggy, take a look around. Is something obstructing the sunlight? 

If the obstruction is something small and minor, then move it out of the way. If the obstruction is something big, like a house, then you’re going to want to move your plants to a different area where they’ll get more sunlight.

If you’ve started your brassica seedlings on heat mats and they appear leggy, turn them off. This might be all you need to do to revive your leggy sprouts and strengthen them up a bit.

If you’ve directly seeded your brassicas and the outside temperatures have gotten quite warm, then make sure your brassicas are getting plenty of water and that they have a good layer of mulch around their base to help keep their roots cool. 

Potting up is just a fancy way of saying to move your seedlings into a bigger container. And when I say container, I don’t mean you need to put every individual seedling in its own container now. You can just transplant your seedlings into a bigger plug tray.

I personally like to use 72-cell plug trays to start my brassica seedlings and then pot them up into a 50-cell plug tray once they have their first set of true leaves. 

If you’re using a seed strip tray, then you have two options. You can either thin out the seedlings so that they’re about 2 inches apart, or you can carefully separate the seedlings and pot them up into some larger plug trays.

If you choose to do the thinning method, you will need to continue to thin them out until they’re ready to be transplanted outside. 

Yes! Leggy brassica seedlings can definitely still be planted. Because their stems are already quite long, don’t be afraid to bury them deeper than you normally would. 

Burying the stem a little deeper will help to support the plant and protect the stem from breaking as most of it will be underground. 

If your seedlings already have their first set of true leaves, then don’t be afraid to bury the cotyledon leaves. 

Cotyledon leaves are the very first leaves of the seedlings that emerged from the ground first. For most brassicas, they look like two little heart-shaped leaves. 

Cotyledon leaves don’t stay on the plant forever and will eventually fall off after the true leaves take over. This is why it’s okay to bury these leaves. But, only as long as your seedlings have their first set of true leaves.

If your seedlings do not have their true leaves yet, then they probably aren’t even ready to be transplanted anyway and should be left in their plug trays.

In Summary

Oftentimes, legginess among seedlings isn’t a big deal, but if left untreated can be detrimental to the growth of your brassicas. 

To recap, here are the steps you can take to treat brassica legginess and help your plants thrive:

  • Move them into an area with more sunlight. This can mean moving them outside, closer to a window, or under a set of grow lights.
  • Make sure they’re not too warm. If your seedlings are on heat mats, turn the mats down. If your seedlings are outside, make sure the soil stays cool with proper watering and mulch.
  • Pot up or thin out your seedlings so that they are not growing too close to one another and aren’t competing for sunlight. 

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