Thinning

Thinning young plants gives them the room they need to grow bigger and stronger. And most people have a hard time with this common garden task.

When to thin seedlings?

While most plant thinning occurs in spring, as new tomato, pepper, eggplant, and other seedlings emerge, the Bay Area is lucky to have a second growing season, filled with salad greens, broccoli, and cauliflower, so the need for thinning comes around again each fall.

A difficult task

For many gardeners, the idea of removing perfectly healthy plants does not come easily. Images of lush, ripe tomatoes, peppers, and melons offer so much potential, that we find reasons not to thin our garden plants. Of course, by not thinning, we compromise the health of all the plants. Thinning eliminates competition, leaving plenty of food, water, and sunlight for the remaining plants. This allows them to reach full size and produce larger crops. Proper thinning also provides good air flow, preventing many fungal diseases.

Thinning basics

Thinning used to mean yanking unwanted plants out of the ground by their roots. This is no longer the case. Soil science has taught us how important tiny soil microbes are to plant health. Pulling plants out by their roots removes the microbes, as well. This makes it difficult for the remaining plants to get the nutrients they need. Pulling plants out also disturbs the roots left in place, which also slows growth. Instead, thinning is done with pruners or scissors, cutting pants off at ground level. This leaves the remaining root systems undisturbed. Plus, it allows the microbes from the thinned out plant to relocate and assist the plants left in place. Snipped off seedlings can be added to the compost pile or fed to the chickens. Just keep in mind that not all crops are thinned in the same way.

Just how much thinning is needed?

Onions and other root plants need frequent thinning. Other plants, such as leeks and beans, perform better without thinning at all. Large, spreading plants, such as pumpkins, need to be thinned out leaving a single plant every 2 or 3 feet! To understand the best way to thin each type of plant, check your seed packets. That information is usually printed on the label. Use it. They know what they’re talking about. If the seed packet is no longer available, look it up online or ask me in the Comments section. You can often calculate spacing needs based on the expected mature size of each plant.

Spring cell packs

Single tomato plants

If you really can’t bring yourself to toss out healthy seedlings, you can always plant individual seeds in peat pots, cell trays, or any other item that will hold a small seedling until it can be transplanted. Of course, this method means extra work in other ways, but it does eliminate the need for thinning.

Do your garden plants a favor and don’t procrastinate thinning!