Coping with Leggy Seedlings

By Caitlin Harwell


If you're a woman, being described as leggy may be a positive, but if you're a seedling it is anything but. So you have carefully chosen your seeds, delicately planted them and now, the new seedlings are just brimming above the soil in their trays on your windowsill and you can hardly contain your excitement.

Perhaps it is the warmer weather that you know is just around the corner, or the excitement of a clean slate after a long winter, but you just can't wait to see the little stems reaching up, and the leaves spreading out and laying small shadows over the soil. When, without warning, the stems have suddenly shot up an inch in three days and the little leaves are bending back over to the soil! You have leggy seedlings.

It is one of the most common issues with starting seedlings indoors. Most gardeners, especially in colder, short-season regions, will begin some of their seeds in their home or their greenhouse in hopes of getting a head start on the season. It is important to let your plants reach maturity before harvesting them, so when temperatures in an area are not typically high enough to plant directly outdoors until April or May, it is advantageous to give your plants some indoor growing time. But in that case, why don't gardeners begin all of their seeds indoors? There are downsides to keeping new seedlings indoors in trays, including:

  • Roots outgrowing soil cells
  • Lack of proper sunlight
  • Dry conditions causing increased water evaporation
  • Damage by curious house pets
  • Lack of proper storage room
  • Poor transplant success rates (beans, corn, radish, cucumber, etc.)

While there may be a long list of reasons that indoor seedlings do not succeed, the most common is when a stem grows too long and thin to support itself, otherwise known as being leggy. In this case the stem will eventually break or will lean over dropping the foliage into the damp soil and causing it to rot or be smothered. So first and foremost, what causes a seedling's sudden growth spurt? Usually it is a lack of light. Just as sunflowers turn to face the sun throughout the day, when seedlings do not receive enough light they will begin to reach towards the available light source, which in turn forces their small stems to stretch and eventually collapse or break. Even a large south-facing window is often not enough light for new seedlings. So what are your options?

  1. Purchase florescent lights. These could be regular table lamps or a store bought seed rack with high-density built-in lights. It doesn't matter as long as they are fluorescent and they reach out over your entire seed tray. Make sure they are only 1-3 inches above the plants; close enough that the seedlings won't stretch and far enough that they won't burn your plant's sensitive new leaves. New seedlings need between 12-18 hours of light per day, but heat from the lights can cause increased evaporation, so be careful not to let the seed trays dry out.
  2. Install a reflective device. It sounds very high-tech but it could be as low-tech as a mirror or a reflective car sunshade that you wrap around the outside of the trays facing the window. In this case, the plants are receiving the light from the sun as it enters through the window and then receiving the reflected energy from the mirror, or other material, as it throws the light back towards the window.
  3. Invest in a small greenhouse. There are plenty of low-cost greenhouses and DIY greenhouse instructions online. Make sure not to move your plants to the greenhouse before the interior temperature of the greenhouse stays above frost temperatures during the nights, especially if your greenhouse has no heat system. The benefit of the greenhouse is that it provides more room for you to house seedlings in an environment where they will receive an ample amount of light (the same as directly sown seedlings). Also, when it comes to soil and water spillage, you can be less careful than you are around your carpets and hardwood floors.

Above you will find some solid ways of providing extra light and protecting your spring seedlings from becoming leggy. But there are other reasons that seedlings become leggy, and one of those is having too many plants in a small space. If you have too many seedlings in a single cell or tray they may begin blocking one another from the light. In this case, their stems will reach up towards the light, and away from their plant brethren, causing, once again, thinly stretched stems. Having too many plants in a general area can also cause them to lean on one another, not requiring them to build strong healthy stems to support themselves. Thin the seedlings out enough that they are not leaning on one another and don't need to compete for light, and soon enough they will be strong and hearty enough to transplant in your garden.

Cait Harwell has been gardening and farming for a good portion of her life and has developed skills in small industry vegetable production and farm maintenance. She lives in the Northeast where she has a small garden homestead and cultivates everything from squash and tomatoes to exotic plants. She recently received her Masters in Writing from FDU and hopes to pursue her life-long dream of owning her own farm.