What Is Thinning Anyway?

Thinning the seedlings is a gardening practice used to 'crowd control' your plants. Very few garden plants like to grow too tightly together, and if they get too cramped, the whole lot will suffer. Although it might seem brutal, thinning your seedlings is a necessity.

Thinning is one of the most beneficial practices a gardener can perform. By thinning your seedlings, you can ensure equal nutrient absorption by those plants and increase their chances of survival. It also allows sunlight and air circulation in your garden, creating a more healthy environment for your plants to grow in. When plants struggle for resources for any reason, they will push all their energies into just the essential seeds, and the 'desirable' side effects, i.e. the produce, will be lost.

Here's how you thin seedlings:

0. Step zero: don't sow your seeds to close to one another! This is setting yourself up for overcrowding. Follow the instructions for any individual seed you sow. Don't go too thin either: many vegetable gardeners sow two or three seeds into each pot, to increase the chance of at least one germinating, then thinning down to one if necessary.

1. Let the seedlings grow until they have two sets of "true" leaves. If you're thinning vegetable seedlings growing in containers, the aim is usually to leave a single, healthy seedling behind in each pot, cell, or pellet. It's finicky work, but you can move thinned seedlings into their own new spaces.

2. Identify and remove the least healthy seedlings. Note that these aren't necessarily the smallest! For example, tomatoes grown on a windowsill may be 'leggy', showing fast but weak growth as they reach toward the light. In these cases, a smaller, bushier seedling may actually be the healthiest of the batch.

3. Ideally, clean your snipping tool (a scissor will do) in alcohol before you start. A fungus or pathogen introduced during thinning can make its way down to the roots and infect remaining seedlings through the soil.

4. Cut off the weak or crowded seedlings. Make sure to cut the seedling across the stem as close to the earth as you can. (Note that in certani cases, such as with carrots, it may be better to pull up the entire plant when thinning. Generally speaking, don't try to pull the seedlings up with your finger, as upsetting the root systems can damage the roots of other seedlings).

5. Consider a light application of fertilizer.

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