How to Thin Seedlings

Planting your garden with rooted seedlings is ideal because the plants are rooted and strong, and it’s easy to allow for just the right amount of space between plants. 

But some varieties like carrots, beets, radishes and turnips, don’t transplant well, and grow best when they’re sown directly into the garden. And since some of the seeds won’t germinate, most direct seeding methods allow for some amount of over seeding. But most of the seeds usually do pop up, which means you’ll have way more little sprouts than you actually need, and will need to ‘thin’ them to allow the healthiest individual plants to thrive and grow to full size.

It’s especially hard for new gardeners to rip out clumps of adorable little sprouts by the handful, but without the essential step of thinning, the inevitable result will be disappointment that ‘the carrots sprouted, but never got big’. 

Timing is key with thinning ; the goal of which is to allow the seedlings to grow large enough to withstand attacks from insect pests, but not so big that they become stunted as they compete for nutrients, and sunlight.To best achieve this balance, and wind up with enough healthy seedlings after some loss to insect damage and weather, most growers thin seedlings in three successive rounds - usually about two weeks apart. 

Perform your first thinning when the seedlings are visibly crowded, and have their first true set of leaves. Make the second thinning, when the remaining seedlings have their second set of true leaves. The third and final thinning should allow for the proper amount of space between each seedling, and performed when there are three of four true sets of leaves. After the final thinning, it’s helpful to gently add mulch - like a small layer of finished compost - around any seedlings that appear stretched. This covers and helps support their fragile stems, and helps ensure that root varieties develop properly. Seedlings can also be carefully transplanted to fill gaps in the rows, where there was no germination.

Consider that thinning is essentially the process of identifying and saving the healthiest, most vigorous plants, and discarding the rest - without damaging the ones you want to keep. When 95% of an over-seeded row of carrots comes up, this can be a tricky test of patience. The standard method of thinning - simply pulling out clumps of unwanted sprouts by the roots - is fast and easy, but can damage the roots of the seedlings that you want to keep. A safer, but slower method is to carefully snip off the unwanted sprouts with scissors, just below the surface of the soil. This method is gentler on the seedlings that stay in the garden, and it yields a neat harvest of tasty, young sprouts.