How To Store Worm Castings

Have you ever been buried under a pile of worm castings? I mean a pile of castings so big... that you can't use them right away?

I've been busy with my Worm Castings Screen Harvester and I've got a pile like that right here in front of me.


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We are going to talk today about a long-term worm castings storage solution.


I am going to take a common cat litter bucket, modify it slightly, and turn it into a long-term castings storage solution.

Before we do that, let's talk a little bit about worm castings and what castings are.

Let's think about what we have to consider when planning a long-term storage solution for worm castings.

Think about worm castings as a living biological entity.


Castings are a collection of bacteria, some fungi, probably a few beneficial nematodes, amoebas, plant growth hormones, and humic acids.

We need to keep our worm castings "alive".


There are two things that castings need to survive. They are moisture and air.

So, any castings storage solution we consider has to maintain the moisture and allow air for the bacteria to breathe.

Keeping this in mind...what are our choices?

Put in a breathable sandbag. This allows for good airflow but dries out quickly.

Not easy to moisten castings without removing them from the bag. Do not recommend for long-term storage. A month or two max.


Use a plastic bucket with a tight-sealing lid and modify to limit air-flow. I use a common cat litter bucket that comes with the lid.

I modify it so there is some air supply. I put moist castings in it, cover with wet newspaper, and put the lid back on.

This will keep your castings moist and aerobic for over a year. You should check the moisture every six months.


This is how we store our worm castings at Iowa Worm Composting. We start with a common cat litter bucket.

This one's a Member's Mark so I'm assuming it came from Sam's Club. These cat litter buckets are all pretty similar.

They are basically constructed mostly the same.

This will apply to most plastic buckets that have a tight-fitting lid. That would include a regular 5-gallon bucket so long as it has a tight lid.

We use cat litter buckets because we have them. You should use what YOU have.

We are going to modify the plastic bucket by drilling some small holes. We use these holes to provide an air supply to the inside of the bucket.

The reason that we use small holes is to limit the amount of air.

This will keep the biological life of the castings intact while not letting too much moisture escape.

What we're going to do is use a drill. I have about 1/8 inch drill bit here. The exact size is not that important.

We're going to drill two holes in each corner so there will be a total of 8 holes in the upper-sides of the bucket.

We want to drill it as high as possible on the side of the bucket because we don't want the castings to come up over top of the holes.

We are going to drill some holes. This is not fancy... you don't need to measure or anything.

We drill the 8 holes and we now have a long-term worm castings storage solution.

I actually sell castings in these buckets. All I do is pull the cat litter labels off and put my own label on.

My label for the worm castings has the directions for use.

I sell most of my worm castings. I always measure how many worm castings are put in the bucket. If you are storing castings for your own use...

this is probably unnecessary. Just be sure that the top of the worm castings stays below the holes you have drilled. Do NOT pack them in.

We want to allow for air flow. Scoop the worm castings in and let them settle on their own.

Cover the castings with a section of a WET newspaper. A 4 sheet thickness is about right. We need to allow for air flow.

Be sure that the newspaper is BELOW the holes you have drilled.

Put the lid on the bucket and seal it up. You are almost done.

The last thing is to write the date on the bucket. I write the date on the side of the bucket.

The reason for this is for vertical stacking. I can stack the buckets up and still see the date.

This is the same reason that the holes are drilled on the side of the bucket.

You should check the moisture of your worm castings every six months at least. This is often enough for our operation.

However, your climate may be different. Starting out...check more frequently until you know your own unique time table.

If you check your worm castings and they are getting too dry...just add moisture to them.

There you have it. We drill a few holes in a common cat litter bucket and Voila! We have an easy, cheap solution for long-term worm castings storage.