Thinning seedlings: Yes, you have to do it.

This week, I’m gearing up for the third and final session of Urban Garden Abundance, the Vancouver-based program I’m leading for Hollyhock, Canada’s Lifelong Learning Centre. In our first class, we built “mini raised beds” out of repurposed wine boxes and planted them up with a variety of veggie seeds – mesclun mixes, lettuce, mustards and scallions. The boxes have served as our platform to explore garden concepts like site design, soil and crop rotation, and to creatively experience the joy of growing food.

Last week, we returned to our roof-deck classroom to see how the boxes had progressed. It had been two weeks since my students had planted their seeds, and in the intervening time I’d taken great pleasure in watering the boxes and keeping them protected through a couple of storms. Everyone was incredibly excited to open up the covers we’d placed over the planters and see that the seeds had developed into healthy baby plants vibrantly bursting with life. It was like opening presents.

But they were less excited when I told them that they’d have to thin their seedlings – in other words, pull some of the healthy baby plants out. I could see people cringe a bit as I did my thinning demo. There were mild protests from the group – did we really have to kill off some of these healthy seedlings, seedlings that they were so proud of?

Yes, they had to do it.

In order to reach their full potential, plants need enough space. Those seedlings that look so cute now are going to grow bigger, and if they’re crowded, they’ll end up leggy or stunted (think beets that don’t actually form harvestable roots). And without enough airflow around each plant, they’ll be susceptible to fungal diseases like powdery mildew, and at a greater risk for all sorts of pests like aphids, leaf-miners and slugs (it’s a shorter commute for the pests to spread amongst plants). Eventually, your soil will become depleted from the overcrowding.

What’s a gardener to do? For starters, plant fewer seeds. Most new gardeners plant WAY too densely and end up having to do extensive thinning. Instead, look at the back of your seed packet. Try to plant at the recommended spacing, not more, until you really know what you’re doing. Remember that more isn’t necessarily better when it comes to seeds.

Second, look at thinning as an opportunity for more food. Most thinnings (except for tomatoes and a few others) are perfectly edible. In the video above, I planted lettuce more densely than usual on purpose, because I wanted to maximize my potential harvest in a small space. By thinning seedlings strategically, I’ll get several harvests at different stages of the lettuce’s growth, starting with microgreens, moving up to baby leaves, and now, in April, full-sized heads. In an urban environment, this technique can be really helpful.

The class perked up when I explained that we’d be washing our thinnings and eating them (roots and all!) for an afternoon snack. See? Nothing is ever wasted in the garden.

Thinning Seedlings: Urban vegetable gardening techniwue

Thinning seedlings (and eating them too)

  • Salad spinner
  • Bowl
  • Scissors
  • A bed full of veggies that need to be thinned

Make sure your soil is moist before starting — it’ll reduce damage to nearby plants and will make your job a bit easier.

Take a good look at the area to be thinned, and visualize roughly how much space each plant will need to grow to full size. Then, gently pull out the excess plants. If your seedlings are very dense, it might be easier to pull them out in rows or squares, and leave a bit extra behind to thin again in a week or two.

Gather the tinnings up into a little bunch. Use your scissors to cut off the roots and drop them into the bowl so that they can easily be dropped into the compost when you’re done.

Put the leafy tops of the thinnings into your salad spinner. Use your hose to gently wash them off, pouring the water back into your garden (not down the drain!). You might have to do it a few times to get all the soil off. Enjoy your salad with dinner!

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