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Compost Guide | Vermicomposting

Compost Guide


Revised On: Nov. 25, 2023 - 8:20 a.m.

The following guidance is for household composting only. For commercial composting, you will need to get notification approval | Learn More >

What is vermicomposting?

Vermicomposting is a form of composting that uses worms (typically red wigglers, white worms and earthworms) to help break down organic matter. Unlike traditional fertilizers, the castings (organic matter processed by the worms) will provide nutrients to plants without the danger of burning the roots.

The two main vermicompost systems are tray-based and continuous flow. The tray system has multiple containers stacked on each other. You add food to the top tray until it is full and then switch to the next one. The continuous flow system is a single container/bag where you add food to the top.

Vermicomposting How-To

Step 1: Make or acquire a bin.

A variety of commercial worm containers are available in different sizes, shapes and price ranges, but worm bins can also be made at home using solid-colored (to keep out sunlight) plastic tote containers with lids. To make a basic bin, drill holes in the side and bottom of the container for ventilation and to drain excess liquid. Then, you can either place the bin in another bin without holes (unless you don’t mind compost directly draining onto a surface), or raise the bin using bricks, add mesh at the bottom to allow for drainage while keeping the worms in, and add a spigot/tap to drain excess liquid. You may also stack bins to create your own tray system. Use a search engine to find an online DIY worm bin guide that will work best for you.

Step 2: Set up the bin.

Fill about ⅓ to ½ of the bin with bedding for your worms. Common materials are shredded cardboard, non-glossy newspaper, finished compost, coco coir, peat moss, straw/hay, leaves and wood chips. Worms breathe through their skin and need moisture to take in the oxygen, so avoid materials that have been treated with chemicals, such as bleached office paper, and keep the bedding moist, but not wet. You should not need to add any more water once you start adding food scraps.

If your bin is outside, keep it out of direct sunlight and bring the bin inside when temperatures drop below 40°F or exceed 80°F. Their ideal temperature for maximum productivity is between 60°F and 80°F. Temperatures above and below this range cause them to eat and reproduce less, and prolonged temperatures below 40°F and above 95°F will result in death. If your bin is inside, the temperature should typically be fine, but in colder months you may need to add a heat lamp or place the bin near a heating vent.

Step 3: Get some worms.

Red wigglers, or red worms, are the go-to worm for vermicomposting because they prefer the compost environment compared to plain soil and thrive in smaller living spaces. Red wigglers can be easily purchased in the fishing section of large retail stores, at a local worm farm or online. If buying online, consider if the outdoor temperature is within the tolerable range for worms and avoid shipping in the summer. You also want to avoid purchasing worms online that are native to much colder climes, as they may require lower temperatures and more space to survive. A bit of research will help you find worms best suited to your environment. 

The number of worms you need depends on how much food waste you generate. A good starting point for a plastic tote bin is 1 pound (about 1,000) of worms. Once the worms have settled in, their population will increase on its own, but you can also add more to adjust to the size of your bin and the amount you compost.

Step 4: Acclimate the worms.

Your new worms need time to get used to their new environment before they start processing your food waste. Before adding worms to the bin, add water to make the bedding moist, but not wet. You can test this by squeezing the bedding. If water drips out, drain the bin or add more dry bedding so your worms don't drown.

Place the worms in your bin and allow them to burrow into the bedding before putting the lid completely on. Light encourages them to burrow. Avoid feeding them for one week.

Step 5: After one week, add small amounts of food to the compost and adjust, as needed.

Start out with small amounts of vegetable scraps. Don’t worry about providing too few scraps in the beginning because worms can also eat their bedding. Make sure to bury the scraps in at least 1 inch of bedding to avoid attracting pests, such as fruit flies.

Leave the worms alone for a week and then check on their progress. Adjust the amount of scraps you add accordingly. If a lot of food is leftover or you notice an odor coming from your bin, consider chopping up the scraps for faster decomposition, reducing the amount of scraps you put in the bin, or adding more worms. If they are eating slowly, check the temperature, moisture, and pH levels of the bin. The ideal temperature range is 60°F to 80°F.

Step 6: After one to four months, check if your compost is ready for harvest.

Once the contents of the bin have a dark brown color, dig deeper into your bin. If you have dark brown contents 2 inches deep in the bin, dig to the bottom of the bin to check for leftover food. If the bin looks dark and earthy throughout, your worm castings (compost) are ready for harvest. If there are still chunks of food at the bottom of the bin, pull them to the top and give the worms another week to process before checking again.

Step 7: Harvest.

Vermicompost is ready for use in one to four months, depending on the size of your worm bin and their productivity.

There are a few methods for separating your worms from the compost to collect the castings:

  • Depending on how fine you want your compost, you can use ¼- to ⅛-inch screen to sift the castings from the worms.
  • Place food scraps and fresh bedding on one side of the bin, wait a few days for the worms to migrate to that side, and then harvest from the vacated side.
  • Don’t feed the worms for about a week, fill an onion bag or mesh bag with food that worms love (watermelon, cantaloupe, banana peels, etc.), bury the bag on one side of the bin and wait 2 days for the worms to migrate. Once they have migrated, you can remove the bag full of worms and pull out the compost, removing any stray worms. Once you've finished harvesting, place collected worms back in the bin with fresh bedding.
  • Dump everything out on a tarp and separate the castings into small, cone-shaped piles. The light will encourage the worms to burrow. After about 20 minutes harvest the top of the pile and put the bottom with the worms back in the bin with new bedding.
  • If you don’t need a lot of castings, shine a light on the bin to encourage burrowing and collect the top layer of castings.

What do I do with my compost? | Learn More >