When To Thin Seedlings? | how to thin out plants

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I’ll be honest with you…


It goes against all of my gardening instincts to cull my prescious plant babies.

However, thinning seedlings is really important and essential if you want to grow healthy vegetables.

What does thinning seedlings mean?

When gardeners sow seeds they usually sow more than they need. This is done because not all will germinate, some will get munched and sometimes we’re just not that careful.

When do you  thin seedlings

So, when your little seedlings start to pop up they will often be too close together and will need thinning.

Thinning is the process of removing some of the seedlings so that the choosen few have space to grow.

Why do I need to thin my seedlings?

Thinning may not be at the top of many gardeners list of favourite jobs but it is an important one.

Too many seedlings planted closely together in a pot, module or row will inevitably end up competing with each other.

Thinning seedlings helps to ensure:

  • sufficient nutrients.
  • sufficient water.
  • access to light.
  • optimum root development.
  • good air circulation which prevents rot and disease.

All these things lead to healthier plants that crop well.

How do you thin seedlings properly?

Some seedlings benefit from being thinned sooner than others. Squash, courgettes, cucumbers and peas have fragile roots that need seperating before they become tangled together.

Other vegetables like spring onions can be planted in clumps or multi-sown (more info below).

How to thin seedlings out…

  1. Seedlings should be at least 3 inches tall and have a minimum of 2 pairs of true leaves before thinning.
  2. Dampen soil before thinning as it will be easier to pull plants up without resistance.
  3. Choose a cooler day or a warm evening to give your seedlings the best chance of recovering.
  4. Gently pull the unwanted seedling or snip with scissors at the base.
  5. Some thinnings respond well to being replanted which is handy if you have gaps along your row. Try this with beetroots and salad leaves.

Remember, that many vegetable thinnings are edible!

If you find yourself regularly thinning loads of seedlings then you can prevent this in the future by sowing seeds more thinly. You can mix small seeds like carrots with sand to make this easier.

Seed thinning spacings

If you look at your seed packets they will tell you the recommended spacings between plants.

You want to aim for these distances when you thin your seedlings although some plants can actually be planted more closely (multi-sown – planted closer together and harvested in turn from each clump leaving more space for others to continue growing).

Usually the space required is the size the plant will grow to plus a few inches either side.

A few examples of thinning spacings:

  • Beetroots: 3 to 6 inches (can be multi sown in clumps of 3 plants)
  • Carrots: 2 to 3 inches
  • Leaf Lettuce: 4 inches (can be multi sown in clumps of 2 or 3)
  • Romaine and butterhead lettuce: 6 to 8 inches
  • Onions: 3 to 5 inches
  • Parsnips: 3 to 6 inches
  • Radishes: 2 to 3 inches (can be multi sown in clumps of 4 or 5)
  • Swede/Rutabagas: 8 inches
  • Spinach: 2 to 6 inches (can be multi sown in clumps of 3 or 4)
  • Turnips: 2 to 4 inches (can be multi sown in clumps of 3 or 4)
When to  thin seedlings
Leeks don’t mind being transplanted in small clusters.

Can I replant my thinned seedlings?

If you want to replant thinned seedlings then there is no harm in trying to re-pot some.

Some plants don’t mind having their roots disturbed as much as others.

“Pricking out” involves separating a cluster of seedlings and repotting them all.

There are a few ways you can prick out seedlings.

  1. Use a chopstick or similar to lift roots carefully.
  2. Soak roots in water before carefully separating.
  3. Gently dividing with your hands.

It’s important that you try not to handle the plant stem. If you need to hold the plant then handling a leaf is far less likely to kill the plant than a broken stem.

Once you’ve got a seedling, plant it up in a pot again or use it to fill in a gap in an existing row.

How to thin seedlings

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