Worm Composting

This is the final installment of my information from the 2014 Carolina Yard Gardening School. (If you missed the previous five articles, please see the links at the end of this post.) Most gardeners are aware of how helpful worms are to our soil. They not only aerate the soil, but they also create worm castings that are full of nutrients. You can either purchase worm castings or create your own through worm composting.

WHAT IS WORM COMPOSTING?

Worm composting, or vermicomposting, uses worms to recycle food scraps and organic matter into compost filled with worm castings (vermicastings). The worm processes the organic matter through its gut, where bad pathogens are killed, and the biproduct is the castings. Castings are very biologically active and high in nitrogen; because of this, pure castings in large amounts can burn plants. However, vermicompost is a combination of worm castings and biodegraded food scraps and bedding. It contains the highly nutritious worm castings, as well as humic acid, and can be added in large quantities to your garden without curing first.

It’s fairly easy to create your own worm castings. All you need are a box with holes, bedding, organic matter, food, and worms. It takes 22-32 days to turn a box of food scraps into vermicompost (compost with worm castings). Worms can ingest 75% of their body weight in food daily! And they double in population every 60 days. However, they do have a short lifespan, so don’t worry about being overrun by worms.

BEST WORMS FOR WORM COMPOSTING

The best worms to use for worm composting are red worms. You can use red tiger worms or red wigglers, too. The reason these are the best to use are:

They can replicate in a composting bin environment.
They have a fast reproductive rate.
They have a short life span.
They can tolerate a wide variety of environmental conditions.

There are various companies that offer red worms for sale, especially online.

HOW TO MAKE YOUR OWN WORM COMPOSTING BIN

Although you can purchase manufactured worm composting systems, they can be expensive. An inexpensive do-it-yourself version can be made very easily. The items you need are:

Ten-gallon colored (not clear) plastic storage bin with cover. (You can move up to a twenty-gallon bin later – or start large from the beginning.)
A larger bin to place the smaller bin into (without cover)
Wood to sit inside the large bin to raise it (for drainage & catching leachings)
Bedding: Choose bedding that is high in carbon (such as shredded newspaper, straw, shredded dried leaves, coconut coir, ripped up cardboard, or dried grass clippings)
Compost
Food: Vegetable & fruit food scraps and dryer lint (yes, dryer lint!) – 1 pound of food per 1 square foot of bin per week
Red worms – 1 pound of worms per square foot of bin

1. Using a drill with a 1/2 inch bit, drill holes in the small bin all along the sides about two-thirds of the way up for aeration. Also drill a good amount of holes in the bottom for drainage.

2. Create bedding in the bottom of the small bin with some compost and carbon bedding mixed together.

3. Add worms and food. Be sure to spread the food across the entire surface.

4. Cover the small bin. Place inside larger bin, raised up on wood. Any liquid leached from the composting bin will be caught by the larger bin and can be diluted in water and used to fertilize your plants.

5. Add food weekly. (See harvesting information below for ways to do this as it depends on how you wish to harvest your vermicompost.)

WHERE TO PLACE YOUR WORM COMPOSTING BIN

Never put your worm composting bin in direct sunlight. A shaded place that is between 59 and 77 degrees Fahrenheit is optimal. If your summers get very hot (like here), you will need to ventilate the top of the bin. But don’t let your bin dry out. Worms need the moisture.

WORM COMPOSTING BIN INHABITANTS

Because you are working with nature to create vermicompost, you will have more inhabitants in your worm composting bin than just worms. Here are some of the critters you may find in your bin:

Soldier fly larvae (adults control house flies)
Pot worms (eat nematodes)
Sow bugs (we call them roly-poly bugs)
Nematodes (mostly good ones that eat the bad ones)
Snails and slugs (possible)

If you have too many soldier fly larvae, pot worms, or sow bugs (which is possible when it’s very hot), you will need to decrease the moisture level by adding more carbon-based bedding. (You should have about 50% moisture level.)

Also, if you see gnats, fruit flies, or roaches, you may be adding more food than your worms can process in a week. Decrease the amount of food a little and increase the bedding.

HARVESTING YOUR VERMICOMPOST

There are different ways you can harvest your vermicompost.

Dump & sort method – After a month or so, you should have some vermicompost to harvest. With this method, dump the entire contents of the worm composting bin onto a tarp or other large piece of plastic. Separate the contents into several cone-shaped piles. Wait about ten minutes, and the worms will crawl to the bottom of each pile. Harvest the compost from the top of each pile. By the time you’ve removed the top of the last pile, you can start again with the first pile. When you get down to the bottom of each pile, scoop up the remaining compost (which will have the worms) and put back into your bin, which should have fresh bedding already added. Add food to the top, and start again, adding food to the top weekly.
Half & half method – When you have compost ready, you can remove half the contents of the bin for your garden and allow the remaining half to repopulate the bin. Continue to add food to the top weekly.
Screen & stacking method – For this method, you will need to have a few screens that fit your bin. When you start your bin, you will put the food on the top of the bedding. A week later, you will add a screen with the food on top. All your food layers will be separated by screens. When it’s time to harvest your vermicompost, you will remove the screen or screens and harvest the compost beneath. (The worms should be on top where the food is, rather than in the compost.)

HOW TO USE VERMICOMPOST

Unlike pure worm castings, vermicompost is safe to use directly in the garden as soon as you harvest it. It’s a great slow-release fertilizer for all parts of your garden. Vermicompost can be used by side dressing seed beds in rows, amending the soil around established plants, or topdressing container plants.

For more information on worm composting, our instructor recommended the following books: