You started your seeds indoors, you thought you did everything right, and then you look at your tall, leggy seedlings with dismay.
What went wrong?
It can be so discouraging to look at those tiny, spindly things… all stem and very few leaves. But, it happens to even the best of gardeners and the good news is, you can fix leggy seedlings most of the time.
What are leggy seedlings?
Seedlings are considered leggy, when they grow tall, spindly, and weak looking. The taller the seedling is, the weaker the stem. These seedlings are typically very fragile, and may even appear yellow or whitish instead of green.
Are leggy seedlings bad?
They’re not generally desirable, no. They become so skinny and tall that they are prone to breakage, dampening off, and other damage. Especially when it comes to the outside elements, like the wind.
While some plants are more forgiving than others, and can be planted deeply when transplanted outside – others cannot, and will just develop rotted stems.
So it’s best to prevent them from happening in the first place. Let’s discuss what causes leggy seedlings.
What causes leggy seedlings?
Young, tender seedlings need adequate light to thrive. They will stretch to try to reach as much light as possible.
A lot of newer gardeners will stick seedlings in front of a south facing window, assuming it provides adequate light. However, this is often not the case.
Many times, seedlings set in a window, will stretch so far sideways to try to get to the light, that they’ll bend nearly in half attempting to do so. It’s really just not an ideal situation.
Seedlings need about 14-16 hours of daylight every day, which the short days of winter do not typically provide. This makes utilizing grow lights necessary for most people.
But even using grow lights requires you keep the lights close enough to the seedlings, or they’ll “reach” for the light and get taller and taller, creating those spindly, long, unsupportive stems.
Too Much Heat
If you leave the heat mat under your seedlings, or don’t remove the humidity dome as soon as they begin to sprout – the seedlings will react with a huge growth spurt.
You’ll wind up with tall stems way before the leaves have had a chance to really grow.
In the forest, plants will compete for light by growing taller. Seedlings are no different. So, if you just scattered those tiny seeds everywhere without utilizing proper spacing, the seedlings will try to grow above one another to reach the light.
We all get busy, but keeping consistent moisture in your seed starting mix is essential. If it’s often drying out before remembering to water it, you’ll probably wind up with some leggy seedlings.
The seedlings will not be able to get the nutrients they need from dried out soil, so they’ll not be able to get the nice, thick stems they need to really thrive and be strong plants.
Preventing Leggy Seedlings
- Provide adequate light as soon as you see those little sprouts coming up. It only takes a short period of time (a day or so) before lack of light will severely affect those little guys and they will stretch up seeking what they need to survive.
- Utilizing artificial light (grow lights) will give seedlings the best chance of growing strong.
- Keep grow lights close to seedlings, about 3″ from the tops. And plan to provide seedlings with light 14 to 16 hours a day, every day.
- Remove, or prop open clear, humidity domes as soon as you see signs of germination – even if only one seedling has broke through the surface. If your dome is clear, you can keep it propped open until you see several sprouts, if you choose.
How to Fix Leggy Seedlings
It happens to the best of us. Once you have spindly seedlings, there’s nothing you can do to prevent it. Thankfully, you can typically remedy the problem.
Provide More Light
Maybe you aren’t using a grow light… go ahead and set one up now. You’ll want to make sure you’re using a broad spectrum t5 or t8 bulb.
Or maybe you are, but it’s too far away, move it so it’s closer to the plant. Or, if you’re using a grow light that is close to the seedlings, try using a stronger bulb.
You can also try multiple lights, this is especially important if some of your trays are in the periphery of the light source. Or, switch out your seedling trays under different lights on different days.
Pull Heat Mats (or Turn Them Down) & Humidity Dome
Heat mats and humidity domes are utilized to speed up plant germination, which is great! But, they’re not necessary after you have some plants germinated, and can encourage sped up growth… something you don’t want when your plants are already looking a bit spindly and frail.
We keep heat mats under tomatoes, peppers, basil and a few other things that need soil temps to stay on the warm side. But, that’s where heat mats with thermostats come in. Setting a thermostat that will allow the mat to turn on when those soil temps drop down below 65°F, will make sure the soil stays warm enough without needlessly encouraging growth.
If your heat mats do not have a thermostat, I recommend pulling those as soon as you see germination, just like the humidity domes.
Use Proper Spacing
Once your seedlings develop their first true leaves, you’ll want to make sure you don’t have them closer than an inch or two apart.
If they’re more crowded than that, you can try to separate them (a gentle process, but not impossible) or simply thin out, and keep only the seedling that appears to be the strongest.
Water From Below
Spritzing your seedlings with the spray bottle regularly may seem to be enough, but it’s probably not. There is no guarantee that water is reaching all the way through the starting mix.
By watering from the bottom, you’ll ensure that the seed starting mix is pulling up the water it needs, all the way through the medium, which will encourage downward root growth.
Use Movement to Promote Strong Stems
A lot of people swear by putting a fan on their seedlings. This can do multiple things – first, it encourages strong stem development because the seedlings have to deal with the constant air movement. It can also prevent some fungal issues and dampening off, because there’s adequate air flow around the seedlings.
If you don’t have a fan, that’s okay. You can simply gently brush your hands over the tops of your seedlings to promote those strong stems. Do this a few times a day for the best results.
Move Seedlings Outside ASAP
As soon as weather permits (check your growing zone for the best advice), you should properly harden off your leggy seedlings and get them out into the soil in the outdoor elements.
Transplant and Pot Up Tomato Plants
The best and easiest way to fix leggy tomato seedlings, is to transplant them up to their lowest set of leaves. This will promote a strong root system and a stronger stem.
In fact, it is best practice to pot up your tomato seedlings at least a couple of times before they’re transplanted outside in order to develop the strongest root system and stem, to best handle the weight of the mature plant and fruit.
This is one of the few plants that will benefit from this technique. Other plants that will benefit from this practice are peppers, eggplants, and tomatillos.
All in all, it’s not the end of the world if your seedlings are a little on the spindly side. A bit of TLC, and they’re likely to bounce right back into healthy little plants that will grow bountifully in the garden.
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