How and When to Thin Seedlings: Tips for Fast Healthy Growth

Thinning seedlings early is KEY to growing big healthy plants, and fast! This quick guide covers the benefits, when to thin seedlings, and three methods to do so – including the pros and cons of each option.

This is one of my top seed starting tips for success. I’ve conducted many side-by-side experiments and comparisons of thinned vs un-thinned seedlings over the years, and the results are undeniable!

I’ve also included a demonstration video at the end, along with a list of which seedlings are edible to enjoy as nutrient-packed microgreens so they don’t have to go to waste.

NOTE: This post was originally published in February 2019 but has been significantly updated since.

What is Thinning?

After planting seeds, thinning is the practice of removing excess, weak, or crowded seedlings in order to give each plant more space. Don’t feel bad doing so! Once thinned, your seedlings will reward you with explosive growth. This applies to starting seeds indoors in containers, and for seeds directly sown or planted outside.

Seedlings can be thinned several ways: by trimming or cutting out extra seedlings (my personal preference), by plucking or pulling out extra sprouts, or by gently separating and teasing them apart – and potting up each seedling into its own container after. See tips, pros, and cons for each option below.

RELATED: Don’t miss our beginner’s guide on Starting Seeds Indoors full of step-by-step tips, tricks, and tools for success – including our DIY seed starting mix recipe. Also, don’t forget to thin your fruit trees!

Benefits of Thinning Seedlings

When left un-thinned, crowded seedlings compete for nutrients, water, light, and root space and therefore grow much slower and smaller compared to those with more room and resources.

On the other hand, thinned seedlings can quickly grow up to four times the size compared to their un-thinned counterparts, in just a matter of weeks! I’ve experienced this first-hand many times over the years. See the example photo below.

Good spacing and thinning practices also increases valuable airflow between the plants, which reduces the risk for pests and disease – especially fungal diseases like powdery mildew.

When to Thin Seedlings

It’s best to thin seedlings within a couple weeks after sprouting, soon after they grow their first full set of “true leaves” (true leaves are the ones that emerge after the initial sprouting leaves). This encourages fast and healthy growth early on, before the plants become stunted or root bound.

If you’re going to thin your seedlings by gently teasing them apart, doing it early also reduces the chance of their roots becoming too intertwined and tangled.

How to Thin Seedlings (Three Ways)

When it comes time to thin, choose the strongest, healthiest seedling to keep around. But that doesn’t always mean the tallest! In fact, shorter seedlings are often stronger than floppy “leggy” ones. I look for thick straight stems and the largest, best-looking leaves.

1) Thinning by Trimming

The easiest, quickest, and most effective way to thin seedlings is to simply cut out the extra sprouts. Use small garden snips to cut out unwanted seedlings at the soil level, leaving just one per cell or pot. Be careful to not accidentally cut the one you want to keep.

With this method, there’s zero risk of disturbing the roots of the “keeper” seedling. It’s also a huge time saver since you don’t have to fuss with potting up or transplanting the seedlings (as you would when teasing them apart).

This is my preferred way to thin most seedlings, especially since we don’t often pot up our seedlings (with the exception of large plants like tomatoes and eggplant). Instead, I like to start most of our seeds in large 6-packs with 2×2-inch cells or small 4-inch pots so they have ample room to grown without potting up.

PRO TIP: Since the extra sprouts are effectively culled, I try to sow only 2 to 3 seeds per cell so I don’t waste too much seed. We also eat many of the sprouts (hello microgreens!) or share them with our chickens. See a list of edible seedlings to follow.

2) “Pricking Out” and Potting Up Seedlings

Teasing apart seedlings (or “pricking out” as UK gardeners call it) is the process of gently separating seedlings from crowded trays or cells and moving them into their own individual pots.

When seedlings are still very tiny, this can be done by using a pencil, dibble, chopstick, butter knife, or other small narrow tool to gently dig down and uproot crowded seedlings – so that you can lift up or “prick out” individual sprouts by carefully holding onto their leaves (with the roots still intact).

For slightly larger seedlings, you’d generally want take the entire soil mass/root ball out of the cell or container and then very gently tease apart the seedlings from one another – taking care not to tear the roots.

This thinning method maximizes the number of seedlings you can start and plant with little-to-no waste, which is great for large gardens, farms, or if you really want to grow out ALL those seedlings!

However, separating seedlings poses some risk of damaging roots, slowing growth, or even breaking seedlings. Plus, you then need to individually pot up or plant each seedling in a new container, which is time consuming and requires more soil, containers, and space (including under grow lights).

PRO TIP: I always heavily sow onion seeds and tease them apart later – they don’t mind at all! I also sometimes gently separate flower seedlings to keep as many as possible. However, I do not recommend teasing apart or pricking out plants with notoriously sensitive root systems including cucumbers, squash, melons, peas, beans, or root vegetables.

3) Pulling Extra Seedlings

Not to be confused with pricking out, a final way you can remove extra seedlings (especially those you don’t intend to keep) is to simply pull and pluck them out by the stem – without the use of a tool to help carefully ease them out of the soil.

However, this is almost guaranteed to damage the roots of the ones you pull up, and also poses some risk of ripping or disturbing the roots of the neighboring seedlings that you’re trying to keep too!

Carrots are the ONLY seedlings I ever pluck out since it’s the most quick and easy way to thin several rows of carrots. I try to thin them within a couple weeks after sprouting, when the carrot roots are still tiny and straight. I also try to plant carrot seeds in a way that reduces my need to excessively thin them (e.g. not seeding too liberally) to reduce this tedious task.

Edible Seedlings (Mircogreens)

If you’ve seen broccoli, radish, kale or sunflower microgreens for sale at the natural food store – those are seedlings! So if you thin seedlings by cutting them out like we do, they don’t necessarily need to go to waste. Plus, tender little microgreens are even more nutrient-dense than their full-size counterparts.

We like to eat our thinned seedlings (microgreens) raw on top of salads, sandwiches, tostadas, or a quinoa/lentil bowl. Our spoiled backyard chickens also go crazy for them! Store microgreens in an airtight container in the refrigerator, with just a tiny splash of water inside to help them stay crisp and fresh.

Edible Seedlings	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	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.

Finally, here’s a demonstration video of me thinning seedlings two ways at our old homestead. (Sorry it’s a tad long, it’s an older video!)

That concludes this lesson on thinning seedlings.

Now that you can see how important it is, I hope this article inspires you to thin your seedlings early with confidence – and without guilt! Please feel free to ask any questions in the comments below

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