Get Started: Worm Composting (Vermicompost 101)

Apr 10

WHAT IS WORM COMPOST?

Also known as vermicomposting, this technique uses an ecosystem of earthworms and microbes to break down organic material into a natural fertilizer called worm castings. Gardeners consider this to be “black gold” because castings have very high levels of microbial activity that enriches soil and promotes water retention. The most popular type of composting worms are called Red Wigglers. This is not the same species of earthworm that you find in your garden soil. They can tolerate a range of environments and are very efficient converters of organic material. At least 1 lb (approx 1000 worms) is recommended for starting a home system. A worm bin is one of the most efficient methods available for composting indoors!

How to build your urban worm bag.

OPTIONS FOR YOUR WORM BAG/BIN

DIY Plastic Tub: This requires a sturdy plastic (10 gallon) tub with holes drilled in the side and bottom for airflow. An option with this design is to “stack” one tub (with holes in the bottom for drainage) into another tub to catch excess moisture. To harvest finished compost, the worms must be separated from castings manually.
Stacking System: This is a popular alternative to the single bin because it avoids water-logged compost and the task of separating finished castings. These stacked bins are made of nesting trays that are placed on top of each other in a vertical tower. The trays have holes or mesh on the bottom, which allows worms to migrate upward when the food and bedding in the lower tray has been converted to castings.
Continuous Flow System: A single container that provides continuous finished castings without disturbing the worms. Food scraps and bedding are replenished on top of the system while the finished castings are removed from the bottom. Worms will naturally migrate to the upper 6 inches of the system where the food is plentiful, leaving their castings below for you to use. This is the design used by the Urban Worm Bag featured in our video tutorial.

Setting up the environment for your worm bed.

CREATING THE RIGHT ENVIRONMENT FOR YOUR BIN

Bedding materials: Popular options include coco coir, aged (not fresh!) horse manure, dry leaves, mature/finished compost, shredded paper and cardboard products including toilet paper rolls, paper egg cartons, and any newsprint that isn’t glossy or colored ink. Remember that the worms will also consume/convert their bedding so you do not want to add anything toxic or inorganic to the mix.
Microbes: A crucial part of the vermicomposting team! Microorganisms break down food scraps prior to worms consuming them. Add a scoop of compost when you start your bin to kickstart microbial activity. If you don’t have finished compost, a scoop of garden topsoil is an excellent alternative.
Moisture: Ideal moisture content is about 60%. The simplest way to determine if your bin is in this range is to squeeze a handful of your compost. You should get 1 drop of water. If the castings are crumbly, the bin is too dry, and you can add more food or water (use mist or spray bottle only). If you get more than 1 drop of water or it’s “muddy,” it is too wet. Add bedding and stop feeding for a period of time.
Temperature: Unlike an outdoor compost bin, the microbes in your worm bin do not need hot temperatures. In fact, the right temperature range in your bin is 40-85° Fahrenheit, but does best at 60-75 ℉. Overfeeding leads to overheating!
pH: This should be neutral to slightly acidic. You can maintain this balance by adding fresh bedding with food scraps. Only add moderate amounts of acidic foods like berries or citrus. Occasionally adding ground egg shells will also help counteract the acidity of food scraps (and the grit is good for worm digestion!)

FEEDING YOUR WORMS

Adding your worms

Feeding your worms

Suitable worm food: Worms can eat most fruit and vegetable scraps, grains such as plain rice and oatmeal, coffee grounds, crushed egg shells, pulp from a juicer, small amounts of bread, and used tea bags. Worms will process shredded or cut up food more quickly and love food that microbes have already started to consume. You can leave food scraps in a container for a few days before adding to the bin. Do you have some veggies in your fridge that are slightly mushy, or brown bananas? This is perfect worm food!
Unsuitable foods: Do not feed your worms butter, meat, dairy, bones, oils, salty foods, grass clippings, citrus, onions, hot pepper, spicy food, pickles or vinegar, pasta, wood ash, and pet feces. Worms do not process these foods well, so they may be left to rot and create odor or breed undesirable bacteria in the bin.
Frequency: Add 25-33% of the weight of your worms every 3 days and observe if the worms finish processing that food before adding fresh scraps. If you see rotting food on top of the bin, they are not consuming it quickly enough and you should add less food.
- Rough guideline for volume conversion of food waste: 1 lb ≅ 4 cups or 1 qt.
Overfeeding: This is the most common error that beginners make. Is your bin too wet or too hot? Does it have an unpleasant odor? You are overfeeding! Add dry bedding and stop feeding until conditions stabilize.

FINISHED WORM CASTINGS

Most vermicompost systems will produce usable worm castings in 8-12 weeks, which is quicker than traditional composting. Finished vermicompost is dark, earthy smelling and moist but not soaking.
Castings can be added directly into a potting mix or used to “side dress” your plants and seedlings!