How to save your seedlings when they are long, skinny and pale

save your seedlings
Leggy tomato seedlings. Credit: Sam Schipani / BDN

There are many advantages to growing seeds indoors, including the control it gives you over the types and varieties of crops you grow. It also allows you to control the means by which plants are produced. But growing seedlings indoors also comes with challenges, such as the maintenance they require.

"Seedlings are like babies," said Jennifer Moreno, president of indoor gardening at National Garden Clubs. “Everything has to be fine. You have to pamper them."

If these conditions are not met, seedlings can become "leggy," which is a term used to describe seedlings that have long, thin, pale stems and small leaves.

“The stem weakens. It cannot be sustained,” Moreno said. “They are basically starving to death.”

Leggy seedlings are not just unsightly. Leggy legs are often an indication that your seedlings will not thrive once transplanted.

“Other things that happen with leggy seedlings is that they don't store as many carbohydrates,” said David Graper, South Dakota master gardener coordinator. "If you have a plant that doesn't get enough sunlight, it won't be able to withstand the rigors of sun and wind."

What causes legginity in seedlings?

The most common cause of long legs is insufficient or uneven access to light. When the light source is too dim or distant, seedlings quickly grow taller to get closer to that light. As the seedling gains height, it sacrifices girth and strength, resulting in spindly, pale, brittle, and stretched stems.

Even if the seedlings are situated in a sunny, south-facing window, the average amount of sunlight from late winter to early spring generally falls short of the 12 to 16 hours required for strong seedling development. Some windows also have coatings that can make it even more difficult for the sun's rays to reach.

"Light can be kind of a challenge indoors," Moreno said. "They get leggy because they're looking for the light, so a lot of times you'll see them lean into the light."

Light can be especially challenging in cloudy areas or northern areas with fewer daylight hours during seed starting season.

“Stretched or leggy seedlings basically happen because they don't get enough light exposure,” Graper said. "The cloudy weather has caused the seedlings to stretch or elongate more than normal."

Overcrowding in seedling pots will also cause leggy as the seedlings compete for light.

"Crowding is related to light conditions," Gaper said. "If plants are close together, they shade each other and compete for available light."

Seedlings can also grow leggy if not watered properly. Similarly, poor soil with inadequate drainage can stunt growth as seedlings struggle to absorb necessary water and nutrients.

Overheating, especially under a germination dome or on a heating mat, can also cause a burst in growth leading to leggy. While warmer temperatures help germination, most seedlings grow best at a maximum temperature of 65 to 70 degrees Fahrenheit during the day and night temperatures of 55 to 60 degrees Fahrenheit at night.

"Too much heat causes rapid growth," Moreno said. "If you have a heat lamp on you and it's too hot, the stems grow faster than the leaves."

How to save leggy seedlings

The first step is to make sure your seedlings get enough light. Moreno said you can try moving your plants to a different south-facing window and regularly rotating the trays to help lean seedlings grow straighter, but artificial light is the easiest way to accomplish this, especially for northern gardeners. with short growing seasons.

Moreno said that he makes sure the seedlings are only a couple of inches from the grow lights. Some gardeners will install a system where the lights can be turned on as the seedlings grow.

Make sure your seedlings aren't crying out for space either. Stagger seedlings an inch or two apart once they develop the first true leaves so they have plenty of room to soak up the sun.

When it comes to addressing hydration, watering from below so the roots absorb water can also help ensure plants get enough hydration.

“A great way to deal with watering and be more consistent is to have a tray where you absorb moisture into the seedlings,” Moreno said. "Add a small amount of water [to the tray], let them sit for a bit and let them absorb."

The quality of your seed starting mix may also be affecting the health of your seedlings. Avoid heavy soil, such as garden soil, and use potting soil or a seedling starter mix that is formulated to have a loose texture with good drainage.

"You may have to see what kind of mix you're using," Moreno said. "You want something that holds water and doesn't dry out too quickly." Moreno recommends looking for seedling mixes with a combination of perlite, vermiculite and peat moss, or making your own. Graper and Moreno said that adding fertilizer to the leggy seedlings' soil will be ineffective.

To avoid overheating, remove moisture domes from seedling trays or remove them from heat mats within a couple of days after they germinate.

Hardening off plants or transplanting them outside can also help with leggy. Most leggy plants get stronger once they grow outside.

It can also trigger stem strengthening through thigmotropism, a plant's reaction to physical contact, by stimulating the movement of environmental stresses in its seedlings. Place a small fan next to your seedlings on a timer to let the plants blow in the breeze for a couple of hours a day and gently run your hand over the tops of the seedlings several times a day to encourage stronger growth.

Some leggy seedlings can be saved with modified transplanting techniques. Because tomatoes have adventitious roots, which are proto-roots that grow out of the plant stem and can grow when exposed to the right soil and moisture conditions, leggy tomato seedlings can also be saved by burying them. stems to the lowest set of leaves. or laying the plant on its side when transplanting or repotting. This method also works for other plants with adventitious roots, such as tomatillos, eggplants, and bell peppers.

When to give up leggy seedlings

Although it can be heartbreaking for gardeners attached to their baby plants, sometimes it's best to cut losses when dealing with leggy seedlings.

“If they get too skinny like that, they won't do very well outside,” Moreno said. "Some of them are like throwing them all away and starting over."

"You can't put it back together," Graper laughed. “If it gets really bad, it would probably be best to plant more seeds in a sunnier spot.”

Moreno said you can often tell when seedlings have passed the point of no return.

“When they get really flabby and they're laying down, I just say they're ready,” Moreno said. "It seems like they haven't been saved anymore, and that's when you want to start over."

Graper said there are two key things to consider: the distance between the first set of blades and the ground, and the distance between sets of blades.

"The distance between the potting soil and the first true leaves should be fairly close to the soil surface, about one to two inches," Graper said. “If it's three or four inches, it's probably not worth dealing with. If there's an inch or so between each set of leaves coming out, it's probably too long too."

However, if you've started your seedlings early enough in the season, you can start over with new seeds in a brighter location.

"Early in the season, there's still time to restart some of these plants," Graper said. “When in doubt, I would say replant.”

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