For those new to the world of growing herbs and vegetables from seed, it is a bit unnerving trying to figure out what you’re supposed to do with the crowded clumps of seedlings that sprout up a few weeks after you’ve planted the seeds. Despite best intentions, it’s hard to plant certain tiny seeds, such as lettuce, spaced according to the instructions listed on the seed packets. And, some seeds that look large are actually clusters of seeds which, by definition, will produce a clump of seedlings. Furthermore, if you start your seeds indoors, as many people living in northern climates do, it’s not practical to plant the seeds properly spaced out, initially, anyway. So, once the seedlings make an appearance, what are you supposed to do to follow the planting instructions that direct you to ‘thin plants to xx inches apart’, and, when, exactly?
Why the need for Thinning Seedlings
Plants need space to grow: they need good air circulation as well as a steady supply of water and nutrients. If they grow all crowded together, they’ll end up competing with each other with the likely result that none of them will thrive. The reason to thin the plants is to create healthier plants, ultimately, with higher yields. So, obviously, the sooner the plants have the space they need, the better.
When to Thin & True Leaves
The best time to thin the plants out is when they have one or two sets of “true” leaves. These are not the “leaves” you see when the seedling first emerges from the soil which are actually called cotyledons. Rather, true leaves appear as the seeding continues to grow which look more like mature plant leaves than the cotyledons, which will wither and fall off, eventually, as the true leaves take over the job of photosynthesis.
The light green rounded leaves are cotyledons
The seedlings will probably be around 2-3 inches tall when the true leaves appear. At this point, your first instinct may be to grasp the the plants in an effort to pull them out of the soil separately in order to thin them out. However, that’s not likely to work very well because their roots will most likely be intertwined, making it impossible to pull up just one plant at a time. Instead, what you should do, as brutal as it sounds, is “sacrifice” excess plants by snipping them off at the soil line.
If, on the other hand, you are determined to “save” the excess plants, you can increase your chances for success by pulling them out while the soil is damp. Also, it will help to do the thinning (and all transplanting, for that matter) in the evening when it’s not so hot and sunny.
Following is a list of vegetable plants that likely need thinning. Listed is a range of spacing, depending on the variety:
- Beets: 2 inches
- Carrots: 2 inches
- Lettuce: 8-12 inches
- Radishes: 1-3 inches
- Onion: 4 inches
- Turnip: 6 inches
- Squash: 18 inches
Young plants grown from seed indoors in early spring need to adjust gradually to an outdoor environment before they can be transplanted—this is called hardening off. Put the plants outside during the day for short periods at first (two hours) and gradually increase the time over the course of a week to include nights as well. Make sure to keep the plants well moistened and watch for frosts. In the meantime, prepare their garden bed by mixing compost and organic fertilizer into the soil.
Once the plants are hardened off and the bed(s) ready, wait for a period when it’s likely to be cloudy and rainy and transplant them into the earth. Water them thoroughly and cover them for a few days to protect them from the elements while they adjust to their new home. If the weather is cool, you can cover them with upside-down pots, buckets or boxes, for example. If it’s hot, fashion a canopy made out of lightweight cloth and garden stakes.