A common vermicomposting conundrum is how to recognize when your vermicompost is finished and ready to harvest your worm castings. This is a tough question, especially if you don’t have a system like the Urban Worm Bag, the Urban Worm Company’s own worm bin which allows you empty the finished contents from below, where worm castings will tend to settle.
The question gets tougher when you are shifting the goal posts by continuing to add new food (and hopefully bedding.) This ensures your vermicompost is never really “finished.”
Let’s say you started vermicomposting a few months ago, didn’t kill your worms a couple times like I did, and have been diligently recycling your food scraps into black gold for your garden.
What should you be looking for to decide now is the time to harvest?
5 Signs Your Vermicompost is Finished and Ready to Harvest
Deep, Dark Brown Color
The majority of your vermicompost has that deep, rich color. While we like to refer to finished compost – both of the thermophilic and worm-related varieties – as “black gold,” an actual black color may indicate your vermicompost is well beyond finished and is now possibly anaerobic. Note: If your worms are fed a steady diet of coffee grounds, this may not apply.
Vermicompost that needs to be harvested will have a uniform texture throughout. However, if you’re the type who grinds your food and bedding together to optimize for faster processing, this may not be the best indicator for you.
Worm Reproduction Slows
As you can imagine, crapping the bed won’t help put your partner in the mood. Granted, worms may have a greater tolerance for staying amorous in their own doody, but everyone’s got their limits. Expect to see fewer cocoons in mature vermicompost.
Small Worm Size
The worms themselves are excellent indicators of a bin that needs to be changed out for fresh bedding and food. Not only will reproduction slow, but the actual biomass of each worm will shrink to reflect inadequate conditions for growth and reproduction.
Flat, Felt-Like Surface
Thanks to Brian Donaldson for using the term “felted” because I had been struggling with a word to describe it. A top layer of vermicompost that has the appearance of black or brown billiards table indicates the bin is ready to be fed, fluffed, or changed altogether.
What If I Have Several of the Above?
If you’re seeing at 2-3 of the indicators above, it’s probably time to consider harvesting the worm castings. In fact, it’s likely your vermicompost is already past its peak microbial population.
This post discusses the various methods of harvesting worm castings and discusses whether you should even bother separating the fine vermicompost from the coarser material in your worm bin.
While simply piling more bedding and food is the easiest way to prolong the tedious task of separating your worms from their castings, it’s a good habit to get some practice using the light method of harvesting or harvest small amounts of castings using a makeshift harvester I designed.
Another easier option for harvesting is to simply feed one side of the bin, wait a few days, then scoop out the finished vermicompost from the other side.
But my most recommended method is moving your bin over to the Urban Worm Bag, a pretty nifty product that allows you to harvest your castings from the bottom by simply opening a zipper. The breathable fabric that makes up this worm bin allows for excellent moisture control. It’s about as close to a continuous flow digester as you can get without spending thousands of dollars.
Were there any indicators of mature vermicompost that I missed? Let me know in the comments below. I’ll update the list as necessary and give you credit!