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How to Thin Vegetable Seedlings

The Spruce / Randi Rhoades

Growing vegetables from seed is much less expensive than buying seedlings from a garden center, but growing from seed also slightly more work. To save time and effort, many gardeners sow vegetable seeds—especially seeds that are very tiny—simply by broadcast sprinkling them in garden beds rather than sowing each seed individually. As a result, too many seedlings sprout and are packed too closely together.   When this happens, gardeners must systematically remove the extra seedlings to provide enough space for the remaining seedlings to grow. Thinning seedlings produces healthier plants and higher yields by reducing competition for water and nutrients and providing good air circulation between plants. Follow these few simple steps to thin seedlings.

When to Thin Vegetable Seedlings

Seedlings are usually thinned when they have one to two sets of leaves. Most plants will be 2 to 3 inches tall by then making them easy enough to grasp and pull out.   If you prefer to pull your seedlings rather than cutting them with scissors, thinning while the soil is damp will make it easier to slip them out without disturbing everything nearby. In addition, thinning in the evening gives the remaining plants a chance to adjust before being exposed to heat and sunlight.

What You’ll Need

Equipment / Tools

  • Kneeling pad (optional)
  • Garden scissors or snips (optional)
  • Flexible rake (optional)

Instructions

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The Spruce / Randi Rhoades

Determine Desired Spacing

Seed packets will usually provide appropriate guidelines for seed sowing depth and spacing. In general, plants should be spaced based on their mature size plus a few inches. Here are spacing recommendations for a few commonly grown vegetables:

  • Beets: 3 to 6 inches
  • Carrots: 2 to 3 inches
  • Lettuce: 18 to 24 inches
  • Onions: 3 to 5 inches
  • Parsnips: 3 to 6 inches
  • Radishes: 2 to 3 inches
  • Rutabagas: 8 inches
  • Spinach: 2 to 6 inches
  • Turnips: 2 to 4 inches

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The Spruce / Randi Rhoades

Remove Unwanted Seedlings

Seedlings can be easily plucked with your fingers simply by gripping them between your thumb and forefinger and giving a gentle tug. This method of removing seedlings is easiest to do when the soil is moist and pliable. If you prefer to avoid disturbing the soil (and nearby plants), you can use garden scissors or snips to cut off the unwanted seedlings at ground level.

Thinning long rows of seedlings requires bending and working close to the ground. Thus, a kneeling pad can be a helpful tool to keep you comfortable.

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The Spruce / Randi Rhoades

Thin by Rake (Optional)

If you are growing vegetable seedlings in blocks rather than rows, you can run a flexible rake through the seedlings to thin them out. However, the seedlings won’t be perfectly spaced. Raking will free up more space for remaining seedlings to grow and is much faster than plucking or cutting seedlings by hand.

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The Spruce / Randi Rhoades

Water the Survivors

Thinning can disturb the soil, so it’s best to lightly mist the remaining seedlings after thinning to rejuvenate the plants.

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The Spruce / Randi Rhoades

Tips for Thinning Vegetable Seedlings

Seedlings started in pots usually don’t have to be thinned because you can separate them when it’s time to transplant them outdoors. However, seeds that are directly sown into the ground almost always require thinning.

How many seedlings you take out—and the spacing you allow for the remaining seedlings—will depend on whether you want your vegetables to grow to full size or if you prefer to eat them early. For example, if you like to harvest tiny carrots, leave the seedlings tightly spaced. But if you prefer large carrots at the end of the season, the spacing should be much farther apart according to the directions on the seed packet.

Root vegetables can be sensitive to thinning because disturbing the young roots can cause deformities. Also, transplanting long-rooted vegetables, such as carrots and turnips, can cause them to fork. So, to thin root vegetables, carefully remove one seedling at a time, either by gently pulling it from the ground or cutting it at ground level. That way, you shouldn’t disrupt the remaining plants.

Finally, some gardeners find it difficult to sacrifice so many vegetable plants. The good news is that some plants—like lettuce, beets, chard, and spinach—is that you can toss the tiny seedlings you remove into salads or other recipes, so all is not lost.

Seeds often sprout too close together and need to be thinned to have space to grow. Learn when and how to thin seedlings.

How to Thin Seedlings (& Get Microgreens!)

Have you planted all your garden seeds, and now they’re starting to sprout? That’s excellent! This also means it will be time to thin them soon. As painful as it may be, it is best to thin your seedlings down to the one healthiest sprout per cell space or container after the first couple sets of true leaves appear. Thinning is a very important step in the seed-starting process to result in the most healthy, successful plants possible! They will thank you with explosive growth!

This post will discuss several methods of thinning, their pros and cons, what to do with the thinned seedlings, and other best practices. A thinning demonstration video is included at the end! If you’re interested in tips for starting seeds, read more here.

Why thin seedlings?

When left un-thinned, seedlings that are in tight quarters will compete with one another for nutrients, water, air, and root space. Those are not things you want to deprive your seedlings of! In addition to concerns about competition, crowding seedlings also increases the risk for disease. This is primarily due to the reduced airflow between the plants. Bad guys like powdery mildew love cramped conditions, and also spread spores when leaves rub against one another. All of this applies to seedlings (or plants) that are started indoors in containers, and outside in the garden.

When to Thin Seedlings

It is best to wait until a couple weeks after sprouting, once the plants have developed a set of true leaves or two, but to not wait too much longer after that. The “true leaves” are the ones that emerge after the first set of sprouting leaves. Those very first ones are the embryonic leaves, called cotyledon, and are often times heart-shaped and indistinguishable between different types of plants. The true leaves more closely resemble what the mature plant leaves will look like, but miniature. Once a few of those pop, it helps you scope out the best looking seedlings.

When it comes time to thin, you get to choose the strongest, healthiest, best-looking seedling to keep around. After thinning, the chosen keepers will take off and thrive! Seedlings can quickly become four times the size of the ones that were left unthinned, in just a matter of weeks! Leaving them un-thinned stunts their development immensely. I have experimented and experienced this first hand, numerous times!

HOW TO THIN SEEDLINGS

Like many aspects of gardening, this is sort of up to personal preference… but here I will share the two methods we primarily use: trimming, or gently separating apart.

A third option is to pull up on the unwanted seedling, manually plucking them out of their container – sometimes with the hopes of keeping the pulled seedling to replant. We do not use or encourage this practice since it can be a bit risky. Not only might the roots of the pulled seedling get damaged, thwarting your efforts to save it, but the seedling you are hoping to save and leave behind in the container may get damaged or completely pulled up along with it.

Thinning Seedlings by Trimming

Our preferred method to thin most types of seedlings is to trim out the unwanted ones. We simply snip off the smallest, thinnest, or leggiest ones at the root line with small sharp trimming scissors, leaving the chosen one behind. We really love these trimming scissors and have several pairs! They’re frequently used on this homestead for many projects.

This is how we thin pretty much all of our vegetable seedlings, whether started in containers or directly sown outside. Aside from trying to reduce potential damage, we also just don’t have the need to save the excess ones. With limited space in the raised garden beds and under the lights in the greenhouse, what the heck would we do with all those additional salvaged plants? We already start more than we intend to grow, as extra insurance. We do not have room for dozens more tomatoes, peppers, or squash on top of that.

Benefits of Trimming:

By cutting instead of pulling, it prevents accidentally distributing the one you’ve chosen to keep – the strongest and thickest looking babe. Since we are not attempting to keep the ones we have thinned out by trimming (as you may do if you are separating them, discussed below), there is no need to pot up or plant out anything at the same time. This makes the thinning process via trimming very quick and easy! All we have to do is snip, and move on.

Note that we also start most of our vegetable seedlings in 4” pots or large cell 6-packs (as opposed to tiny peat pellets or smaller cell packs) which also reduces the urgency to pot them up early. This makes trimming even more appealing for us, as the plants do not need to be fussed with for any reason at the time of thinning. The plants will all be happy in their homes for quite a while, especially after they are thinned.

Potential Drawbacks:

Some people view the loss or “death” of these extra seedlings as a negative thing – an overlooked potential of future plants, or even as a waste. But we do not view it this way! Here is why:

Microgreens!

The ones we cut aren’t “going to waste” just because we don’t replant them! The thinnings are nutrient packed micro-greens. We eat them. Or most of them at least.

Which seedlings are edible? So many types! For example, any baby greens like lettuce or kale, other brassicas like broccoli or kohlrabi, or basically any veggie that you could otherwise eat the foliage of – are edible microgreens! You will find a more complete list below.

These make for an excellent salad or meal topper! We use them mostly raw but can be cooked as well. They also make for a super high-class chicken treat. After cutting them, microgreens stay most fresh and crisp if refrigerated inside a sealed container, like a glass tupperware or ziplock-type bag, with a tiny splash of water in with them.

Here is a list of edible seedlings,
and also those you want to avoid consuming
Edible Microgreens Do Not Eat – Compost instead
Kale
Spinach
Radish
Arugula
Beets
Carrots
Celery
Turnips
Pea shoots
Cabbage
Collard Greens
Mustard Greens
Basil or other herbs
Lettuces
Onion/Leeks
Swiss Chard
Bok Choy
You get the point. A lot!
Tomatoes
Peppers
Eggplant
Cucumber
Melon
Green Beans

Potato greens – except for
sweet potatoes, they’re okay!

Rhubarb leaves are toxic!

Squash are a maybe?
Some cultures enjoy
eating pumpkin leaves!

Look at all these micrograms we ended up with from thinning!

Thinning Seedlings by Separating

Another method used to thin seedlings is by gently separating them. To do this, carefully remove the whole chunk of soil, seedlings and roots out of their small container. You can usually accomplish this by by gently tipping the container on its side and easing the mass out, pushing up from the bottom as needed. Do not pull up on the seedlings themselves!

Gently break up the soil and pull the seedlings apart. As much as possible, take care not to forcibly rip the roots apart if they’re tangled together. Next, either immediately re-pot the ones you want to keep, or get them planted outsidebut only if they’ve been hardened off first! (Post coming on hardening off next week!)

I use this method most often for flower starts, like sunflowers and zinnias. In my humble opinion, there is alwaaaaays more room for flowers in the garden! Especially zinnias, because they’re a monarch favorite! So I like to try to keep as much of those babies alive as possible. They’re usually pretty hardy and can handle this treatment. Also, we usually plant out flowers a bit earlier and smaller than our veggie starts. This means that when I separate them, I can plant them straight outside right then, not needing to repot them. We also do this with fava beans. The tomatoes and peppers need to be babied in the greenhouse for a bit longer.

Demonstrating the separation method with zinnia seedlings.

Benefits of Separating:

One benefit of pulling apart seedlings is that you can exponentially increase the number of plants that you are keeping. You could also potentially increase the number of plants that you’re able to start in a smaller space.

For example, if you only have one small shelf and grow light, you could fill one tray with six 6-packs. By using the trimming method, cutting them down to just one plant per cell, the result would be 36 plants. But if instead you separate out the multiple sprouts from each cell, you could easily end up with over a hundred plants! That is a lot of bang for your buck. However, once you separate them, they do need to go somewhere. That leads us to the potential con of this method:

Potential Drawbacks:

When you separate out seedlings, but it’s not yet time to plant them outdoors (e.g. they’re still too young and tender, you haven’t hardened them off yet, or there is still risk of frost) then they’ll need to be potted into individual containers. If we are following the previous example, now what are you going to do with 100 individual containers? Even if you have room for all those in your garden, do you have space and light to keep them happy in the meantime – until they go outside?

Another drawback of this method is the time that it takes. If you need to either pot them all up or plant them all out at the same time as thinning, it makes the process of thinning much more labor-intensive. This can make you less eager to get the task done and procrastinate on thinning, which isn’t in the best interest of the plants! I have felt this way several times, and feel similarly about potting up.

The final potential issue with this method is the risk of harming the plants. As long as you’re gentle and separate them early, many plants do okay with some root disturbance. They usually will not die, even if handled a bit rough. But when I do have to get rough with them, I can’t help but think “How would they have done if I hadn’t torn them apart like that?… Would they be even larger and more robust?”, especially if the plants are doing just so-so out in the garden later. Because while they may not die, root disturbance can cause a slight shock and setback in development.

Some plants have a super sensitive, delicate root system, and do not like to be disturbed at all.

These are ones that should not be thinned using the separation method. They should either be started directly outside in their final destination (called direct-sowing) or use the trimming method to thin them instead.

The following plants do not like to be transplanted, or are sensitive to root disturbance:

  • Beans – direct sow preferred, though early gentle transplanting can be successful
  • Nasturtiums – direct sow preferred
  • Carrots – only direct-sow in place
  • Radishes – only direct-sow in place
  • Squash and Zucchini – okay to start indoors, but do so in a large enough container that they will not become root bound, and transplant out and/or pot up before they do
  • Beets – same notes as squash
  • Spinach – same notes as squash
  • Peas – same notes as squash
  • Melon – same notes as squash

Alright folks! That is the low-down on thinning seedlings! My thoughts and experience with thinning seedlings, that is.

So, whaddya say? Are you feeling a little less nervous about the situation, and ready to go snip off (or separate) some babies. Baby plants, I mean…

If it was time to thin your seedlings, it may also be about time to fertilize your seedlings for the first time too! Check out this post all about how, why, and when we use seaweed extract to fertilize seedlings. It is a gentle, sustainable, and effective multi-purpose organic fertilizer. We love it, and so do the plants!

I hope you found this helpful! If so, share it! Feel free to ask questions in the comments below.

Thinning is very important step in the seed-starting process. Learn how to thin seedlings to get the most healthy, large, and successful plants possible!