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The pros and cons of starting seeds with worm castings (vermicompost) | CoMo Homestead
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Most of the weed seeds are tomatoes, with a few peppers thrown in here and there.Most of the weed seeds are tomatoes, with a few peppers thrown in here and there.
I almost didn't take photos because I thought this was so embarrassing, but eventually decided to do it for the good of the food growing community.I almost didn't take photos because I thought this was so embarrassing, but eventually decided to do it for the good of the food growing community.
Starting weed seeds. Unfortunately.Starting weed seeds. Unfortunately.
  • Most of the weed seeds are tomatoes, with a few peppers thrown in here and there.
  • I almost didn't take photos because I thought this was so embarrassing, but eventually decided to do it for the good of the food growing community.
  • Starting weed seeds. Unfortunately.

I recently read an article about a study that found that using worm castings in your seed-starting mix can help prevent damping off. I’ve never had a problem so far with damping off, but since I have a ready supply of worm castings at my disposal, I figured it was worth a shot.

Here’s what I’ve found so far:

Pros:

  • Can prevent damping off
  • Provides nutrients to the seedlings

Cons:

  • SEEDS. One of the unfortunate things about vermicomposting is that the worms don’t do anything to deactivate any seeds that you might put in your compost. All the seeds you put in the compost will return out of it, unchanged. This means that if you add the castings directly to your garden bed, you’re introducing “weed” seeds into you garden  (they may be tomatoes, but if they’re unwanted tomatoes, they’re weeds). And if you add the compost to your seed-starting mix, you’re introducing weed seeds into what you want to be a seed-free environment, except for the seeds you are actively planting. This is a problem.
  • Dries out more easily. I use a standard Jiffy-style organic peat-based seed-starting mix. The peat holds water really well, which is wonderful because I often forget to check on and water the seedlings. (Sidenote: I recently discovered capillary mats, and am excited to try out this lazy man’s efficient form of seedling irrigation.) Using the worm castings, though, the soil blocks have dried out much faster. This can be a problem with seed-starting, because you’re trying to provide the most favourable environment possible so the seedlings can get off to a strong, healthy start. I used about half a tray of worm castings to about ~15 quarts of seed-starting mix. I have no idea if this is a proper ratio. It’s possible that I used way too much, and that’s why the blocks dried out. Either way, though, this is a good thing to know: worm compost doesn’t hold water like peat does.

To me, the seeds that have popped up are the most challenging aspect of this. I can control the water, but I can’t control the germination of weed seeds. Plus, the weed seeds can potentially a) get in the way with or interfere with the germination of the seed you actually wanted to plant, b) when you pull the unwanted seedling out, there’s a possibility that you could damage the desired seedling and c) if you let the weed seeds get too big, they could potentially steal nutrients away from the seed you’re trying to grow.

I’m not anti-worm compost for starting seeds at this point, but I think I’ll need to be much more careful about what goes into our compost. I’ve tried to keep seeds out of the compost, but there have been a few moments of weakness in the middle of a canning session when I’ve dumped a bunch of tomato seeds into the bucket. Lesson learned.

In the future, if I want to use worm castings in my seed-starting mix, I think I’ll need to put the castings under lights for a few days to let any existing seeds germinate. At that point they will be easy to remove, and then I can add the (mostly) weed-free compost to the rest of my seed-starting mix.

I was really excited about the worm compost study, but as it turns out, it’s slightly more complicated than you would hope. Oh, science.

25 Responses to “The pros and cons of starting seeds with worm castings (vermicompost)”


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