How to Thin Seedlings

How to Thin Seedlings

What is 'thinning', why is it done, which seedling varieties require it, and how many seedlings should be kept?

Some seed varieties require the process called thinning, meaning that excess seedlings which have germinated are removed to provide the necessary space for the plants to thrive. Root vegetables like radishes, beets, and carrots require thinning of seedlings to eliminate competition for resources and space. Ten carrots trying to grow in a 2-inch pod will result in a crazy nest of twisted roots with very short and thin carrot production, while their above-ground tops may look bushy and beautiful. Large fruiting plants like tomatoes and peppers are similarly thinned so the remaining seedling can absorb as many nutrients as possible and won’t get crowded out by a bedmate.

We recommend thinning seedlings when they are still young, between two to three inches in height at two to three weeks of age. At this point in their life cycle, the strongest, healthiest seedlings should be apparent and easy to identify. The weaker, smaller seedlings should be the ones removed. Some varieties like tomatoes and carrots require greater thinning for space than other varieties like basil. See the table below to determine how many seedlings of each plant variety should remain in a pod.

Although the plant variety and the number of seedlings to keep may differ, the process of thinning is the same for all varieties. The goal is to remove excess seedlings with as little soil disruption as possible, while still moving all, or most, of the root structure.

  • First, water the soil surrounding the seedlings well. This will soften the soil and make the process more gentle.
  • Next, identify the strongest seedlings you plan to keep and those you plan to remove.
  • At the base of the stem, grasp the seedlings you plan to remove, one at a time, and gently tug from the soil, preferably removing the root system as well as the above-ground foliage.
  • When all of the unwanted seedlings have been removed and set aside, gently pat down the disturbed soil surrounding the remaining seedlings.

The seedlings that you have just removed can be composted, eaten as micro greens (if edible variety), or if their root structure is intact they can be transplanted into another planting container so they can continue their journey to maturity. 

Seedling Variety Thin Seedlings to:
Basil 2-3
Beans 2
Beets (as root veggies) 1-2
Borage 1-2
Broccoli (crown and sprouting) 1
Buzz Buttons 1-2
Calendula 2
Carrots 1-2
Cauliflower 1
Corn 2
Cucamelon 2-3
Cucumbers 1-2
Eggplant 1
Emerald Oak Lettuce 2
Fennel Bulb 1-2
Ground Cherry 1-2
Marigolds 2
Melons 1
Nasturtium 2
Peppers 1
Radishes 1-2
Squash (inc. zucchini & pumpkins)
Sunflowers 1
Tomatillos 1
Tomatoes 1
Zinnia 2

Leave a Comment