How-To: Worm Composting

What is it?

Worm composting, or vermicomposting, involves the breakdown of food waste into a nutrient-rich compost through the action of worms and other microorganisms. Red wigglers (Eisenia fetida) are the most commonly used variety of composting worms because they are surface dwellers that live in rich organic material and can eat around half of their body weight a day in food waste. From this waste they produce castings, a form of excretion that is incredibly nutrient rich and can be applied to gardens and farms.

What type of bin do I use and where do I store it?

Bins can take a variety of forms, but are most commonly made out of plastic or wood.

Worms survive best in temperatures ranging from 55 to 77 degrees. That doesn’t mean the air outside has to be that temperature, only the inside of the box. On cold days, the microbial action will keep bin temperatures well above the outside air temperature. Always keep your bin in a shady spot because direct sunlight is the fastest way to get a bin that is far too hot for the worms. A good way to test is to touch the bin. If it’s hot to the touch, they need to be in a cooler location.

What makes good worm bedding?

We recommend using newspaper that has been torn into thin strips (shredders work great!) This is a free, waste-stream material. Only use newsprint which uses soy-based ink (most newspapers use soy inks.) Do not use shiny advertisements or magazines as worms will stick to the surface and the ink may be toxic. You want your bedding to be fluffy, like packing material. The goal of the bedding is to keep the food scraps aerated and oxygen rich, and to absorb extra moisture. If the bin is too wet and dense, the material may go anaerobic. 

How do I feed my worms?

Dig down into one corner of your bin and dump your food there. For your next feeding, move a few inches over from your first feeding location, dig a little hole, and feed there. In this way, you will work around the bin, which will make harvesting easier later. If your bin is too small for this, simply feed the bin in halves. Feed one side for a couple of weeks, and then feed the other side. Every time you add food to the bin, cover it with bedding to soak up moisture and to reduce pests and smell.

Ideally you will feed your worms every 2-4 days. However, worms are flexible. You can feed them as often as every day or as infrequently as every other week, depending on your needs and goals for your worm bin. If you need to get your food waste off your counter every day, go for it. If you go on vacation, your worms will be fine for a couple of weeks without care–assuming you give them a big helping of food waste before you leave, and their bin doesn’t get too hot or dry. 

What should I feed my worms?

Red wigglers don’t actually eat your food, they eat the microorganisms that eat decomposing organic matter. You can feed them the majority of your kitchen food scraps. Non-citrus fruits, vegetables, tea bags, coffee grounds and filters and crushed eggshells are great. Manure from horses, cows, and rabbits are good as long as you let them compost a little on their own first. Grass clippings and other leafy yard waste is also fine. Paper towels and other soiled paper products are also acceptable. Some notable exceptions:

1. Limit onion and garlic skins. They skins are carbonaceous and break down very slowly. It will be a long time before they are ready for the worms and could start smelling before they become worm food.

2. No citrus. Citrus peels contain limonene, which is toxic to insects.

3. No meat or dairy. It attracts rodents, and won’t decompose at the same rate as the vegetables so may start to smell.

4. No pet or human feces. This kind of bacteria is bad for worms and gardens.

5. No oil, and limit oily food. A little cooked food is OK, but worms breathe through their moist skin. Oil will smother them.

TIP:  You can also blend your food scraps before adding them to your bin. This will create more surface area, allowing microorganisms to break the food down more quickly, which in turn will allow the worms to turn it into castings faster.

How do I harvest my compost? 

Find the areas that you fed longest ago and are the most broken down and remove them, placing them on a tarp or other surface in a pyramid shape in the sun. Worms are light-averse, so will dive below the surface to escape the sunlight. Wait 5 minutes and remove the top layer of castings. Continue this process until all your worms are together at the bottom of your pile. Return your worms to your bin.