Welcome to the third post in this series about how to build and take care of a simple worm farm. Be sure to check out the first two posts if you haven’t already. The first one will walk you through how to build a worm farm using plastic storage containers. The second post in the series has all the details about feeding your worms. Now, let’s move on to my kids’ favorite part. It’s time to harvest the worm compost!
Worm Compost vs Worm Castings
Worm castings (a.k.a worm poop) is the microbe and nutrient rich material that is harvested from a worm farm. Yes, that’s right…worm poop! My kids get a big kick out of that. As gross as that may sound, it’s just one of several manures that gardeners love to use. It takes at least 120 days for the food and bedding material in a worm farm to be processed enough that you’ll have mostly castings. Vermicompost is a combination of decomposed material (like regular compost) plus worm castings. The longer the worms are able to process the material, the more castings will be in the finished compost material. As a classroom/homeschool project or an average home gardener, you don’t need to worry too much about this distinction.
Just keep in mind that the compost is ready to harvest when it is dark and crumbly. You shouldn’t be able to tell what the bedding or food was. If you’re going for more pure castings, you’ll want to let the worms process the material longer and aim for 120 days.
Two Worm Compost Harvest Methods
The Migration Method
Once you decide to harvest, feed the worms only on one side of the bin. Remember to only add new food once the previous food is almost gone. They will continue to process the other side and then move to the side with the food. The migration can take a few weeks. Once they have moved, you can harvest the castings without having to pick out many worms. If the top layer of that side is not fully processed, you can dig down and scoop out the castings underneath. Add fresh bedding to take the place of the castings you harvested. Now, start adding food only to the side with the fresh bedding. Once the worms have migrated to that side, you can harvest the other. Add fresh bedding to the other side once it has been harvested.
The Light Method
The light method is most fun for kids but can be a bit tedious for others until you become fast at it. Stop feeding the worm farm and let them finish processing the material. Once you can’t identify any food or bedding materials, you can harvest. If you don’t want to wait you can dig down and scoop out the finished material that is beneath the layers that are still being processed.
Spread out a piece of plastic or several layers of newspaper over a table in an area under a bright light. You can empty the bin little by little or dump the whole thing out at once…depending on the space and time you have. I prefer to do it little by little because it can take me a few days depending on the size of the bin. Plus, my kids like to help me…as in the photo below.
Pile the compost into a cone shaped hill under the light. The bright light will force the worms down into the pile. After a few minutes, scrape off the castings from the top and sides of the mounds until you start finding worms. Leave them alone for a bit and they will move further into the mound. Repeat the scraping of the top and sides until you find worms again. Keep repeating this process until you are left with just piles of worms. As you’re harvesting the worms, prepare new bedding for your worm farm. Add the worms back into the farm.
My kids love to help harvest the castings and pick out the worms.
Screening Worm Compost
Some people like to screen the compost before using it in the garden. This isn’t all that necessary for home gardeners and hobby worm farmers but you can sift it through a 1/4″ screen. Anything that doesn’t fit through can be tossed back in the worm bin. An 1/8″ screen will catch most of the baby worms and cocoons (worm eggs), which should also be put back into the worm farm. Baby worms and cocoons can also be easily spotted by using the light harvest method. My kids love to see who can find the most! Check out the picture of a cocoon and a baby worm below.
Look for these cocoons. You just may see a worm hatch! Here’s a baby that just hatched and another one is coming out.
How to Use Worm Compost
Worm compost is a bit different than regular compost. Regular compost is normally used by the shovelful and spread over a garden area in a 1″-2″ layer and mixed in. Worm compost is used by the handful. My favorite ways to use worm compost…
- mix a handful into each hole when transplanting
- mix into the soil in areas that are direct seeded
- use a handful to side dress plants a few times during the growing season
- make aerated compost tea with it
- use it in a seed starting mix, up to 30% of the mix
- gross out my kids and their friends by touching worm poop!
Finished Worm Compost a.k.a vermicompost
How to Store Worm Compost
If you have finished compost but you don’t immediately need it in the garden, you can store it and use it later. Just keep it moist. The beneficial microbes will begin to die off if it dries out too much or is stored too long. This is a big difference between store bought worm castings and those from your own worm farm. Freshest is best. Store bought products are often too dry and stale.
Thank you for joining me on this adventure of building, feeding and harvesting a simple worm farm! Composting with worms is my favorite way to compost because it’s so much easier than building a huge compost pile in the backyard. Most kids have a strong reaction to worms which makes it so much fun. Some love them and can’t wait to dig in, and others work hard to get up the courage to just touch one. It’s fascinating to to watch them help with the worms.
Other Posts in this Series
Post #1 in this Series –How to Build a Worm Farm with Storage Totes
Post #2 – How and What to Feed Your Worms
More Garden Fun with Kids
Gardening with Kids – Child Led Activities
Favorite Butterfly Books and Hands-On Activities
Thank you for your great article on harvesting worm castings. You mentioned in another article on feeding the worm farm – not to “blend” the food: “Whatever you do, PLEASE do not blend the scraps! Blended food can “disappear” easily into the bin which makes it hard to see. Many new worm farmers who try this end up killing their worms by overfeeding them. There’s just no need to blend and it’s very risky.”
I don’t understand what is the difference between blending and pureeing the food in a blender.
Hi Suzanne, I don’t see a difference between blending and pureeing either when it comes to feeding worms. I just chop the scraps so that they’re about 1″ in size or smaller. Many scraps are already small just from prepping the veggies, such as carrot and potato peelings. Aside from the “disappearing food” issue that can lead to over-feeding, using a blender is an extra step that just isn’t needed, and it creates more dishes to clean. I hope that clarifies a bit for you. Thanks for stopping by!