Harvesting Worm Castings: 4 Foolproof Methods

Ed Wike
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How Earthworms Respond to Food, Moisture, and Light

Soil beneath the surface isn’t only where the action is in regards to worms; it’s also where the best conditions are for the worms to live and reproduce. Once they set their sights on a spot, they will burrow in and set up shop. Here are a few things that they want in order to live a happy life and produce the most worm castings.

The first is food. Earthworms are very much like us in that sense. They enjoy a balanced, healthful diet. You can give them their recommended daily allowance of organic material, and they will be your lifelong loyal servants. Worms like to dine on partially decayed plant matter and decaying leaves. Earthworm poop or castings is a mix of their own fecal matter, bacteria, and partially digested food.

Earthworms are extremely sensitive to moisture levels. When they are sitting in a puddle of water, they are likely to drown. They need consistent levels of moisture to help them digest their food.

Earthworms also like above ground areas. The worms need to get some amount of sunlight every day.

Last but not least, like us and a lot of other living things, worms like the company of other worms. They like being near other worms of appropriate size. They also like being among their siblings.

4 Easy Methods to Help You Harvest Worm Castings

Worm castings can be used as a natural fertilizer for plants, and this has led to a rise in the number of worm composting enthusiasts.

When harvesting worm castings, a lot of people prefer the vacuum method. This is because it is the most clean and easy way to harvest them.

The worm casting vacuum is attached to a long tube, which you then use to suck out the castings inside the worm colony. You can then transfer the castings to a compost pail or just leave them in the worm colony itself.

The other methods do not use a vacuum. Instead, you pour the worm castings out and then compost them.

One of the most popular methods is the using-a-pail method. Using this method, you place the castings inside a bucket after removing the worms and the tray.

You then place the bucket in your outdoor compost bin and wait until the worms have produced more castings. Repeat this until you have enough worm castings.

To use the worm bucket method, you either need to re-start the worm colony or use a brand new one. You can use the original worms and simply transfer them to a new home with new bedding. Worms die in extreme temperatures, so avoid doing this in the summer.

Manual Sorting

If you want to extract only the best castings, then manually sorting and screening your compost tea is the way to do so. After all, hot water extractors only filter particles larger than 5 microns, which is way too large for healthy castings.

Too small of particles can also be extracted with the hot water extraction method, which makes manual sifting critical.

Manually sorting is not a difficult task, but it does take time and patience. It also requires some specific tools. What you will need:

  • Shop vacuum with hose attachments.
  • 1-inch wire screen,
  • that you can obtain locally. (This is a standard size, so you should be able to find it at a hardware store.)
  • Paper coffee filters, as well as cardboard for temporary use.

{1}. Obtain organic compost that is particle-based, without chunks of large matter, such as sticks, leaves, grass, or husks.
{2}. Spread your compost on a large tarp and run a shop vacuum over it. Make sure that the screening attachment is wide open. This allows as many particles as possible fit through the 1-inch wire screen.

Bait Method

This is one of the easiest 4 foolproof methods for harvesting worm castings. It is simply planting food scraps, or letting the worms eat your food scraps.

For bedding materials (this is used in part to give the worms a place to live, and in part for trapping the worm castings as they fall. This is optional), you can use a variety of bedding materials. Some examples include compost, leaves (composted if possible), straw, shredded paper, or newspaper (shredded).

Lay out your bedding materials in a box, biggest layer first, and then the smaller layers on the top, so the worms can have a variety of textures and conditions.

The smaller compost materials will work great to plug the holes and make sure that the worms stay in the bedding and don't escape.

For food scraps, keep an eye out for food particles, and peelings that can be fed to the worms: banana peels, apple peels, leaves, carrot peelings, etc. Worms also like orange peels and coffee grounds.

If you have cold and warm seasonal temperatures, two boxes are a good idea: one for the cold months of the year, and one for the warm. This reduces the amount of work you do in the summer/dry season, freeing you up for other activities.

Light Method

The “light” method of harvesting worm castings is similar to the “mix” method. It is also known as the “newspaper” method. You simply add several layers of newspaper to the top of your worm castings bedding (as many as three or four layers). This method is best used for beds that are nearly 100% worm castings when the castings are harvested and not mixed with soil.

The newspaper method is the best for harvesting worm castings if the bedding is low in moisture. The paper acts like a blotter, absorbing the moisture until it reaches a certain moisture level (which you can see by lightly poking the paper). If the bedding is too wet, it will take forever for the newspaper to absorb it all, so you should use this method when the bedding is nearly 100% worm castings.

The newspaper will remove too much water when the bedding/castings are too wet. When this happens, use the mix method.


(compost sifting)

Screening the worm castings is easier than it sounds.

Basically, you use a screen that looks like a big metal mesh.

In the picture below, you can see a 3/8” (a bit more than 0.9 cm) mesh screen used to separate the worm castings from the food scraps.

The food scrap is left on the bottom.

The worm castings are put in the bowl.

It is very important to use a non-toxic mesh.

The castings can have harmful organisms like salmonella in it. These organisms are very resistant, so the best way to destroy them is to kill them with heat.

You can bake the castings at 180 degrees Fahrenheit for 30 minutes or put them in the oven on the lowest setting for 24-48 hours.

The time depends on the quantity of castings you are making and the humidity in the air. You want them to be dry but not burned.

Once you have screened the castings for at least one layer of the mesh, put them in the oven for one hour for every pound of the casting.

If you don’t have a mesh screen, you can put the castings in a large paper bag and shake them through.

Harvesting Worm Castings Easier With The Urban Worm Bag

When farming worms for the purpose of extracting organic, partially composted worm castings, harvesting is a very important part of the process. It allows you to make use past the cocoon stage, so you know that you aren’t wasting any nutrients or precious bedding materials. The problem, however, is that harvesting worm castings can be a frustrating and messy chore.

Many people have very well water and tap water, or their local water source is heavy in chloramines or chlorine. Because of this many people end up dumping the castings into their outdoor beds. These castings are nutrient-rich and perfect for the garden, however, the same chemicals that kill algae and mosquito larvae in the water, can kill your plants and seedlings.

But worming beds is a tricky business because it can take a long time for your bedding to decompose all the way down to a level at which you can harvest it. This can lead to a lot of wasted bedding over a 2- to 3-month period, depending on what you are using for bedding. The reason it takes so long is because of the increased volume of the bedding materials compared to the amount of castings that you get per worm.