You can help eliminate floppy, pale seedlings with a few simple tricks. Millie Davenport, hgic.clemson.edu
When you start your own vegetable, herb and flower seedlings at home, one common problem is that they become leggy, a bit floppy and lighter green than normal. This is called etiolation and a certain degree of it is actually quite normal for seedlings started under less than perfect conditions. The difference is especially clear when you compare homegrown seedlings to the trays of dark green, dense, compact seedlings produced in commercial greenhouses.
This is often just a minor problem, not one to get too upset about: once even somewhat leggy seedlings are planted outdoors, they tend to correct themselves and take on a completely normal appearance and coloration. But still, there is a difference between seedlings that are just a bit leggy and ones so weak they can’t even stand upright.
Here are some tips on what to do “make things better”:
1. Don’t start your seeds too early. Any seedlings started before their time will tend to etiolate seriously. It’s actually better to start your seeds a bit late than too early. To discover when to start each kind (and yes, the dates will vary depending on what you sow and where you live), look at the seed pack for directions, get out a book about growing from seed or look on the Internet (Seeds to Sow Indoors, for example).
2. Reduce the temperature after the seeds germinate. Most seeds germinate best when kept quite warm (70–74 °F/21–24 °C), but after they sprout, they prefer things fresher. At that point, therefore, place seedlings in a spot where the temperature is cooler, especially at night: ideally around 65 °F/18 °C, even 55 °F/12 °C for some. That can make a huge difference!
3. Give them more light. Most seeds are fairly indifferent to light as they germinate, but afterwards, become real lighthounds! Provide as much light as you possibly can, placing the seedlings near a south-facing window, setting them up outside in a temporary greenhouse or placing them under a fluorescent or LED grow light that you keep lit 14 to 16 hours a day. In the latter situation, the closer the seedlings are to the light, the better. Just raise the height of the lamp as the seedlings grow so they don’t quite touch the lamp.
4. Give seed trays a quarter spin. If they’re on a window sill or any other place where sunlight reaches them laterally, that is. Otherwise, seedlings from the side of the tray furthest from the window well receive less light than the others and will start to bend and stretch looking for more. This is easy to fix. Just give the seed tray a quarter turn, always in the same direction, once or twice a week. That will give your seedlings a fairer share of the light and keep them nice and straight.
5. Shake’em Up! Gently shake the trays 2 or 3 times a day or run your hand back and forth over the seedlings at the same frequency, touching them gently. Or use an oscillating fan (set to the lowest speed) to make them move. This replicates the effect of wind and helps to make the stems shorter and stronger.
6. Thin’em Out. When the seedlings grow too tightly together, it creates competition for light, water and minerals and thus stimulates etiolation. Never hesitate to thin out your seed trays, leaving only the strongest seedlings.
7. Gently fertilize. Most seedlings live on their reserves at first, plus the average seedling mix contains a bit of fertilizer, but when they have 4 to 6 true leaves, their need for minerals increases and they’ll weaken when those minerals are lacking. Every second watering, therefore, fertilize with a soluble all-purpose fertilizer applied at half the recommended dose.
It doesn’t take much to turn weak, floppy seedlings into healthy ones you can be proud of!