In a previous issue, Jack Shoultz discussed hot-method composting, where the organic material generates heat as it rots, and he explained the benefits of using compost in the garden. In this issue I'd like to discuss another type of composting, one that does not generate heat: worm composting, also known as vermicomposting.
Using worms to turn organic material into a nutritious garden amendment is not technically composting because the material is not decayed or rotted. Rather, it's digested – by the wondrous earthworm.
I say wondrous because the castings coming out of the worm are much richer than the stuff that went into the worm. Castings (the polite term for worm poop) contain a myriad of beneficial organisms, growth regulators, yeasts, molds, humic acid and a smorgasbord of nutrients. When spread in the garden, earthworm castings cause magical things to happen to your plants.
Abra cadabra
A blade of grass sitting on the ground contains potential nutrition for your garden, but until it is rotted or digested (or both), the nutrients are not readily available to your plants. When an earthworm ingests that blade of grass, it is not going after the grass, but rather the microbes (especially protozoa) on it. In the worm's gut, the microbes on the grass are digested for their nutrients while the grass itself is ground up into tiny pieces (think blender).
The finer the grass is chopped, the more surface area is created for bacteria and fungi to attach to. Amazingly, the worm's gut has lots of beneficial bacteria and fungi that happily move onto the blenderized grass. As this grass stew continues to move through the worm, the bacteria and fungi begin to digest it and store the nutrients inside of them as biomass. Eventually, the worm eliminates this nutritious stew in the form of casts (poop). In a healthy garden, biomass nutrients are readily available to plants.
Benefits of Worm Castings
(1) Improved plant growth and bloom production. Worm castings test low for N-P-K in a traditional soil test. However, they are nutritional powerhouses because biomass nutrients are so readily available to your plants while at the same time are protected from leaching from the soil.
Ohio State University has conducted several studies on the effect of vermicompost on plant growth. They have found that adding as little as 5 percent worm castings to a commercial planting mix resulted in dramatic improvements in growth.
(2) Soil softening. Soil that lacks beneficial biology can become hardened. Adding worm castings, which contain an abundance of beneficial organisms, provides the biology needed to return the soil to a softened state. Plants can form larger root systems in softer soil.
(3) Biological decomposition. Vermicompost can increase the rate at which other organic materials in the soil decompose. For example, decomposition of prawn and crab shells is doubled when worm castings are added to the soil. This happens because castings add a lot of beneficial organisms which decompose the shells.
(4) Fungus control. Vermi-compost can control fungus problems when applied regularly. Fungi are an important part of healthy soil, but too many of the wrong kind cause nitrogen lock-up and other problems such as fungi on your rose leaves and stems. Fungus-eating protozoa and nematodes in worm castings will control fusarium, rhyzoctonia, phytophthora and sclerotinia fungi, and will improve plant growth with the release of excess nitrogen as the fungi are brought into balance.
(5) Insect repellency. Several microorganisms found in worm castings are effective insect repellants. For example, for hard-shelled bugs, worm castings contain chitinase-producing organisms. Chitinase is an enzyme that will dissolve a bug's exoskeleton. Obviously, a bug isn't going to hang out where its body will get dissolved. Bugs have various ways to determine the level of chitinase in soil. Once the chitinase level is high enough, they will leave the area.
Some elements in worm castings are able to activate the chitinase-producing organisms found inside plants. Once triggered, the organisms multiply to a level that can be detected by bugs sitting or chewing on the plant itself!
(6) Odor elimination. Worm castings have been found to be more efficient and less expensive than activated charcoal at absorbing unwanted odors.
Making Your Own Magic
Adding the benefits of worm castings to your garden is easy. Perhaps the easiest way is to head to your local garden center and buy a bag of vermicompost. WormGold is a common brand, and one that I have used and can recommend. However, I much prefer to make my own vermicompost. It's fun and a whole lot easier to do than thermal composting.
With thermal (hot-method) composting, it's important to have the correct proportions of green stuff to brown stuff so your pile heats up properly. You also have to turn the pile regularly to add oxygen, and keep it properly moist. I was never very good at hot composting, mainly because I had gobs of horse manure (green stuff) and practically no browns (leaves), so my piles frequently became anaerobic. Worm composting has none of these problems. You simply toss in all the stuff and let the worms do their thing. In a few weeks you'll have your own magical worm poop.
To become a worm wrangler, you'll need a container. A simple plastic bin with a lid and plenty of holes for aeration and drainage will work, or you can purchase a commercial bin. The experts say you need approximately 1 square foot of bin surface area per 1 pound of food waste produced in a week. A family of four produces about 7 pounds of food waste per week and would need a bin with 7 square feet of surface area.
Next, you'll need some Eisenia foetida redworms. These "red wigglers" are especially active in the worm bin environment. They will eat almost anything you give them and are prolific breeders. Ordinary garden earthworms require soil to survive and would not be happy in the worm bin environment. Redworms eat about three times their weight per week.
Two pounds of redworms in a bin will eat about 6 pounds of food scraps per week. So, if you've been paying attention, a family of four will need a little over 2 pounds of redworms in a bin that has about 7 square feet of surface area. However, don't let the bin size suggestion prevent you from getting started! My first bin was a Worm-a-Roo, which only has about 1 square foot of surface area. Seven years later, it's still working hard for me and handles about half of my kitchen scraps.
Okay, you have the bin and a pound or two of redworms. What next? Before adding the worms to your bin, put in a layer (approximately 1 inch thick) of carbon-rich bedding. Newspaper works great. Simply shred it into 1-inch wide strips and toss it into the bin. Water the bedding until it's as damp as a wrung-out sponge, then add your worms. It's best to feed your worms lightly for the first couple of weeks.
An ecosystem needs to form within the bedding and food waste. As the populations of bacteria, fungi and other critters increases, the bin will be able to process more food scraps. After the start-up period, you can feed your worms daily or even once a week. After each feeding, cover with a layer of moist bedding. Redworms will eat most foods, though you'll want to leave out meat, dairy and fats, which have a tendency to putrefy. The worms won't mind this, but you will!
The trickiest part about vermicomposting is getting your hard-working worms out of the castings when you are ready to use them. It's not a disaster if some redworms go with the castings to your garden, but if you want to keep your worm bin at peak production, you'll need to keep as many worms as possible in the bin. One benefit of commercial bins is that they have a system for removing the worms from the castings.
The Worm-a-Roo is a lateral-movement bin. It has two bins side-by-side with a door between them. When one side gets full of castings, you start the other side and open the door so the worms can migrate to the fresh side. The worms will go to the new food, and after a week or so, the finished castings will be mostly worm-free and ready for use in the garden.
Worm castings are rich. Think of them like fertilizer, not mulch. You don't want to put down a 6-inch layer of vermicompost like you would mulch. Rather, spread a 1/2 inch layer throughout your garden, scratch into the soil if you can, water, then wait and watch.
Garden Magic
If you've seen an earthworm in your garden, it left behind some vermicompost. The more organic material you add to your garden, the more worms will come and the more vermicompost they will deposit. Worms in the garden do more than leave behind their black gold. As they burrow and travel through the soil, they stimulate soil microbial activity. As they eat organic matter and soil particles, they mix up the soil in a good way.
Charles Darwin calculated that worms can turn over the top 6 inches of soil in 10-20 years! By fragmenting organic material and mixing the soil, earthworms increase soil porosity and aggregation (clumping), which significantly increases the water-holding capacity of the soil. The channels made by deep-burrowing earthworms are lined with readily available plant nutrients and the burrows themselves make it easier for roots to penetrate deep into the soil.
The best way to increase the worms in your garden is to apply lots of organic material so localized worm populations will be drawn to all the yummies – sort of the "If you build it, they will come" idea. Good materials to use include:
- Alfalfa hay and meal
- Oat straw
- Composted redwood mulch
- Compost (be sure it's tested and certified)
- Fish meal
- Cottonseed meal
- Shredded newspaper and cardboard (yup, they make a good mulch, especially under a layer of alfalfa hay)
If you live where the ground freezes, you might think that encouraging earthworms in the garden is hopeless. Not so. While most adult surface-dwelling worms will not over-winter in freezing temperatures, worm eggs (cocoons) are amazingly hardy. Cocoons can easily survive even Alaskan cold to hatch a new generation of baby worms when spring arrives. And so the magic continues.