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Why, When, and How to Thin Plants in the Garden

Why thin plants?

Some plants germinate less reliably. While succession planting is useful, when we plant a certain section of garden, it is nice to end up with a fairly uniform coverage so that we can get the size harvest that we want. We might be aiming for enough at once for dinner or enough at once to efficiently preserve, but we usually have a certain crop size in mind.

Not all seedlings will thrive and survive. It may be an issue of pests or weather, but some crops are more prone to trouble, so we over-plant in hopes of getting the right number of plants in the end. When we are blessed with great results, we have to thin out some of the plants so that the rest can grow well.

Why, When, and How to Thin Plants in the Garden

What is thinning?

Thinning is the polite way of saying “weeding out unwanted plants.” Although most people think of a weed as a totally undesirable plant in any location, practically speaking thinning is a subset of weeding because the plant is not wanted where it is.

Plants need a certain amount of space to grow to full maturity. How much space depends on the plant and it’s growth habits. The right amount of space allows them enough room for roots to expand, for top foliage to spread, and for adequate amount so air and sunlight to get to them.

You can coordinate thinning and transplanting in some cases, as I talk about with both balsam impatiens and cucumbers, for example.

Which plants need to be thinned?

thinning cabbage beans onionsPartly this depends on how you are getting the plants into the garden. You almost never need to thin plants that are transplanted because you can space them just where you want them. You will often be doing this at the same phase of growth as when thinning needs to be done. Here are some common plants that are usually over planted on purpose when they are direct seeded outdoors, so might need to be thinned:

  • corn
  • cabbage
  • cucumbers
  • squash
  • pumpkins
  • melons
  • pumpkins
  • broccoli
  • Brussel’s sprouts
  • lettuce
  • onions
  • spinach
  • basil
  • dill

What doesn’t (or maybe not always) need to be thinned?

  • thinning peppers violasbeans
  • peas
  • potatoes
  • cilantro
  • asparagus
  • transplants from pots usually include tomatoes and peppers
  • plants grown from bulbs or roots, such as potatoes or garlic

Which plants are hardest to thin?

thinning carrotsIn my experience, root crops like carrots and beets are particularly difficult to thin. For carrots, it is because the foliage is so fine and hard to differentiate between plants when they are small. For both carrots and beets it is because the roots of nearby plants are easily disturbed. If the seeds can be spaced according to package directions, it is better.

When to thin?

At the very least you want to thin when the young plants have just started touching leaves. They may touch again when they are mature, but since they have reached full size it isn’t as detrimental as when they are trying to grow. Thinning could be anywhere from 2-6 weeks after sprouting.

As I mention in the video, you shouldn’t just wait until the plants are super big. They won’t grow right when crowded, but will either stay small or grow skinny. They will not recover from being stunted or crowded.

How to thin carefully

How careful you need to be depends both on the plant type, how close together the seedlings are, and how mature the seedling is. When plants are younger, many of them seem to handle some root disturbance better. That is because they are in growth mode and just get back to sending out shoots.

Here are some hints:

  • plant seeds according to package directions to avoid unnecessary thinning and to have plants spaced so that thinning is easier
  • thin when the soil is damp, and therefore looser
  • thin in cooler temperatures so that any damage from root disturbance is not exacerbated by heat
  • evenings are a good time to thin so that plants have the cool of the night to recover if necessary
  • plants that have been disturbed benefit from a slight watering in again, just like after transplanting
  • mark the plants you have chosen to keep so that you won’t accidentally thin them
  • consider placing two fingers alongside the base of a plant being saved when it is very close to those being thinned, then gently hold it down while somewhat slowly pulling the others out
  • think about thinning in stages if you want make sure enough of them survive, as I do when dealing with cabbage maggots on my cole crops
  • don’t forget you can eat some of the seedlings that you thin, particularly lettuce, spinach, onions, beets, and carrots
  • if plants are too close or too mature, consider carefully pinching or clipping the unwanted ones to soil level

Thinning is well worth the effort

thinning corn squashThinning might seem difficult or brutal at first, but once you get the hang of it it will be easier. It will get you better gardening results and you will get better at it. Doing it at the right time makes it less work. A little experience with it and it will get faster and easier. Do you have any plants that need to be thinned soon?

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