Outdoor Worm Bins: An Easy Way to Produce High Quality Compost
Are you interested in worm composting, but you don’t want or can’t have a worm bin inside your home?
Or have you been worm composting indoors successfully, but just aren’t able to create enough of their awesome compost in such limited space?
In many climates, it’s quite possible to create large worm bins outdoors. Given a little protection, it’s often feasible for worms to survive the winter. My sister and I created a 3 foot wide by 4 foot long by 20” high worm bin inside our unheated hoop house. We harvested 50 gallons of worm castings from this bin this spring! That’s almost $200 worth of compost created in just a few months from a small space.
Studies have shown that vermicompost (worm castings) is one of the most beneficial types of compost that you can provide your garden or containers. And it’s pretty expensive to purchase! You can easily spend nearly $30 for a single 40 pound bag.
My sister and I started out a few years ago with an indoor worm bin, which has worked well for us. However, we eat a LOT of fruits and vegetables, and we found that we always had more peels and food scraps than a single indoor worm bin could handle.
So, we decided to experiment with a homemade worm bin inside our hoop house. We stacked a couple of old wooden cold frames on top of each other, and filled it full of shredded leaves, chicken manure, grass cuttings, food scraps of all types, and a few handfuls of soil to supply the worms with grit. You could also use moist shredded newspaper and a little peat moss, too.
We keep the bedding mixture moist, and add fresh food a couple of times a week. A scrap piece of cardboard is kept on top of the bedding to shade the worms from the sun and to help reduce evaporation.
Our unheated hoop house (high tunnel) offers plenty of winter protection for our worm bin in our climate. We’re in a southern zone 6b, where it only occasionally drops below 0 F, and most of our daytime highs are above freezing.
Winter daytime temps inside the hoop house are usually around 50-65 F, with lows in the 20’s – though we have a few nights that might drop to the mid-teens. Our worm bin is large enough so that the center stays warm enough for the worms, even when the temp in the hoop house drops below freezing overnight.
Red wiggler worms (the type usually used for composting) can die if they are exposed to freezing temperatures (though the worm egg cocoons can survive prolonged periods below freezing). Some people in climates as cold as Chicago and Colorado have successfully kept worms alive outdoors all winter, often with the use of a large worm bin (sometimes sunken in the ground), a thick insulation of leaves or straw, and a covering of a plastic tarp.
Regularly supplying plenty of fresh worm food (kitchen scraps) also provides a little heat through decomposition (though worm composting is generally a cool composting method). Even if the worms die, their eggs will hatch come spring to start a new population.
Our outdoor worm bin has been easy to create and manage, and we can harvest a large amount of high quality compost from it a couple times a year. In fact, it’s worked out so well for us that we’ll be selling our indoor worm bin and just using the one outside.
What’s been your experience with worm composting?
I have an indoor written farm but need more castings then it can provide. I live in 8b zone in Texas so cooking the worms would be worrysome. I have two compost piles that are so slow, they dry out quickly even after heavy rains So the wood boxes would help and placing in shade. What did you line the boxes with too keep worms inside. Many years ago tried earthworms outside in large wood box. They all escaped.
We didn’t line our bins with anything, but we did have densely compacted crushed stone on the floor of our hoop house, which probably prevented the worms from traveling into the ground. The best way to keep worms in your bins is to provide ideal living conditions, so they don’t want to leave. Plenty of fresh food, moist enough conditions (but not too wet), and not too hot and not too cold. The composting worms will prefer to stay in a healthy worm bin, rather than leave.
You are right to worry about excess heat in your location. So providing shade and possible surrounding the box with a thick layer of mulch might help. Make sure you are using composting worms (red worms or red wigglers) and not regular earthworms from the garden. They prefer different conditions.
Also, if the worm bin has been used for a few weeks or months, the high level of castings will start to repel the worms. That’s when the bedding is getting ready to harvest. The worms periodically need access to fresh bedding. We move all the used bedding to one side and add fresh bedding next to it. Then we start feeding them only in the new bedding. They will finish up the old bedding and move over to the new bedding when they are ready.
I have several 5 gal buckets of worm castings mixed with organic potting soil. I want to sprinkle these buckets of compost into my beds. Should I do it now and let it winter in or wait until spring planting time.
Hi Marcia, I’d probably wait until spring planting time. That way nutrients won’t be leached away from the winter rains or snow melt.
Hi Debra! I live just 30 miles east of San Francisco with my husband in a condo. As it can get quite hot here in the summer (every now & then, triple digits for 5-6 hours during the day), I was afraid that above-ground worm bins might cook my worms. So, I just dug a 2′ x 3′ hole in the ground & threw in my red wigglers with some cardboard & kitchen scraps. These red wigglers can consume a whole ‘personal sized’ watermelon rind in about 5 days. I feed them every 2-3 days with minor scraps, leaves, coffee grinds, etc. So I figure these worms are happy worms! The worms also work so fast that I have no issues with attracting varmits. I’m sharing just in case you have other gardener friends in warmer climates or more crowded conditions.
Hi, Joyce! That’s very smart! I’m glad you shared your experience. You’re right that worms can die from extreme heat, so your below ground bin is a great idea for your climate.
I had an indoor worm bin for a season. didn’t like the messy work of separating the worms from their castings in order to get the ‘harvest’. So, I quit and put the whole thing into the outside compost pile.
I do live in a zone 8, ie pacific northwest coast, so could try your hoop house solution, but again the separation effort would be too fiddly for me…. your image and text don’t convery how you did that step? I don’t imagine you shovelled directly from the bin into your 5 gallon pails, although the image seems to suggest that….
I do enjoy and appreciate your emails, posts and blogs. thanks!
Hi, Sue! In your climate, the worms may do just fine outdoors with a windbreak and some insulation around their large worm bin. Yes, we do shovel directly from the bin into the bucket (see my reply to Bern). Other than keeping older bedding in one half of the bin, and newer bedding in the other half, we don’t do any kind of separation of the worms from the finished castings.
How do you harvest your worm castings? The pic shows a spading fork, which doesn’t look like it would pick up much castings. And it looks like the castings are in the bottom of the bin, so you’d have to excavate below the leaves to get to them. And how to separate the leaves from castings? I’m a little confused.
Hi Bern! Our worm castings were moist enough that the spading fork did mostly OK until we reached closer to the bottom, when we switched to a trowel.
When the worm bedding starts to look like it’s getting pretty decomposed and starts shrinking, we shovel all of it to one side of the worm bin. Then we add fresh bedding to the now empty half, and only add food scraps to the new half. The leaves you see are part of the new bedding.
The worms continue working the older bedding until it’s well decomposed, and then most of them finish migrating over to the new bedding. So we don’t do any fiddly separating of the worms from the bedding. There are always some worms in the finished castings that we shovel out (along with egg coccoons), but they are just added to our potting soil or garden beds along with the castings. Most of the worms are in the new bedding with the food. We try to keep things pretty simple. Does that help?
Thanks for this wonderful article. I have created a compost bin from a big black plastic bin. I even bought wriggler worms and put fresh kitchen scraps once in 2/3 days . I collect them in the kitchen.
However I am not sure my compost is ready although I started this in April. Not sure what I am doing wrong. It does not stink , and I am aware of the browns and greens combination.
Summer is over and I wonder if I need to buy more worms to get my compost created.
Hi Asha! If the bin was working well, your earthworms should have multiplied, and the bedding should be breaking down into compost. Do you see plenty of earthworms?
Thank you for responding.
I do not see any worms on the top. I may need to shift the food waste and see if there are and let you know. I can collect some pics and send them over if there is a possibility.
Asha, you should be able to easily see the worms by digging around in the bedding, especially where you added fresh food a week ago or so. If you want to send me photos, you can find my email address on my about page.