One of the reasons my soil is so productive is because I use a lot of worm castings, or worm manure, that I harvest from a worm bin that I made myself. In this video, DIY expert Todd Brock and I show you the steps to make your own outdoor worm bin so you too can have access to an endless supply of free worm castings.
Gardeners everywhere know that compost is black gold for the garden, but vermicompost is the best of the best — and farmers pay big bucks to add it to their garden soil. The cool thing is we can make vermicompost at home for free, and it’s the very best fertilizer we can put into our gardens. Not only that, it reduces the amount of waste going to landfills and couldn’t be easier to make.
Unlike regular composting, which can be done in a big sprawling pile outside, vermicomposting needs to be fairly well contained. A plastic bin or tote is a popular choice, and it’s usually stashed in a basement or pantry. Some people even keep it underneath the kitchen sink. For others, having a bin full of garbage and worms is a little too much Mother Nature to have inside the house.
An outdoor bin can be larger while still being safely contained, and it can produce much more vermicompost than a plastic tote can accommodate.
The Best Materials for an Outdoor Worm Bin
Cedar or redwood will hold up great outside in the weather. To keep the costs of your worm bin down, you can also use pine or pallet wood. However, be sure to avoid pressure-treated lumber, which has chemicals that will be toxic to the worms and can leech into the vermicompost that you’ll be adding to your garden, where you don’t want toxic chemicals.
A 4×4, some lengths of 1×8 and a few 1x4s are all you need. Our bin measures about 4 feet by 20 inches, but you can make your bin any size you want.
How to Assemble the Worm Bin
Short pieces of 4×4 will be the interior corners of three shallow boxes that will make up the worm bin. The 4x4s give the boxes their structure and provide something solid to drive nails into. Just make sure all the 4x4s are cut to the same length. Ours are cut to match the width of our 1x8s.
Only the bottom box will get a true floor, made of 1×8 planks, and it serves as a tray to capture the worms’ liquid waste with drip pans. You can even cut a latch into the bottom of the tray and add hinges to make it easy to remove and replace the drip pans.
The other two boxes get a floor made of wire mesh. Buy a big roll of it and cut it to size with tin snips. This allows the worms to move freely from one box to the other and lets the castings fall through as they’re made while you keep replenishing the scraps from above. The wire mesh is secured with a handful of screws with washers that are larger than the holes in the mesh.
In this worm bin design, the boxes are stackable and interchangeable so as one box fills with castings, you always have at least one empty bin to add scraps to. The 1x4s become the legs of the bin and help lock each box in place when they’re all stacked.
The remaining 1×8 planks become a lid for the bed, held together with cross pieces of 1x4s. Add a handle to the top to make it easier to work with, and that’s all there is to it.
Siting a Worm Bin
When picking a location for your worm bin, convenience is important, but so is shade. Worms can’t take heat above about 85 degrees Fahrenheit. If the bin gets that hot, the worms will cook to death, and you don’t want to come out to a bunch of dead worms.
For convenience, I picked a spot next to my compost pile and my garden. When I bring materials to my compost pile, I can decide which to divert to the worm bin. And then the finished product is right there in the garden, so it’s the best of all worlds.
What You Can Put in A Worm Bin
When adding organic materials to a worm bin, follow the same rules used for regular composting. The things you really want to avoid are meats, dairy and grease. But other than that, worms are not picky eaters.
Kitchen scraps and scraps from the garden, like banana peels, apple cores, carrots tops and wilted lettuce, can go in, as well as paper and cardboard household waste. Size is important though, so shred junk mail and paper towel rolls before adding them to the bin. The smaller the pieces going in, the quicker they become finished product.
You may want to avoid fruit in an indoor bin to avoid attracting fruit flies, but in an outdoor bin, it doesn’t really matter.
What Worms to Use in a Worm Bin & How to Keep Them Happy
You can’t use just any worms that you find in a worm bin. The type of worms that can survive in a bin and are the most effective are red wigglers. These can be purchased online or found at a bait shop. In this case, a neighbor gave me two pounds of worms, which is about 2,000 worms.
The worms like moisture, so when you add red wigglers to a bin, lightly mist the inputs. They also hate light, so don’t be surprised when they immediately go down under the materials that you added to the bin. The worms will pass through the mesh to get to the food they want.
Once the worms finish eating what’s on the bottom and turning it into vermicompost, they will work their way up to get at the newer materials you’ve added.
How to Collect Worm Castings
Collect castings from the middle bin, and when it’s empty, switch the middle bin with the top bin. This way, the inputs that are furthest along or completely turned into finished vermicompost will always be in the middle bin, and the top bin will have room for more inputs.
The hardest part is keeping the worms fed. They are voracious eaters that multiply readily. But the worms will reward you with valuable vermicompost for a thriving garden.
Do you raise worms to get castings for your garden? Let us know your keys to success in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges.
Disclosure: Some product links in this guide are affiliate links, which means we would get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us. None of the items included in this list have any bearing on any compensation being an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.