Introduction

Vermicomposting is a method of using worms to process biodegradable organic waste such as kitchen or garden waste. The nutrients in the organic waste are broken down by interactions between the worms and microorganisms to form compost that improves the fertility of soil. The compost is made of castings, which is the worms’ manure. Worm castings improve soil structure so that it is better able to hold moisture and they also increase the availability of nitrogen, potassium, phosphorus, calcium and magnesium in the soil.

Small scale vermicomposting can be used to recycle household waste and is often done in simple boxes, trays or containers of different sizes. Almost any container can become a worm bin. In Southern Africa, the most commonly used type of composting worm is the Eisenia foetida worm, also known as the red wriggler.

Vermicomposting produces one of the best natural fertilizers available and is attractive because of its low investment costs and its sustainability. Vermicomposting can be done in urban settings where there is limited outdoor space and is odourless if done correctly. In addition, unlike with landfilling, there is no methane gas produced during the vermicomposting process and it produces less carbon dioxide than conventional composting.

The Worms

The red wiggler worm is able to consume organic waste equivalent to roughly half of its body mass each day. For example, 450 grams of worms can process about 225 grams of organic waste per day, although this varies depending on the worms’ appetites. As a rough guide, the organic waste that is produced by one to two people will usually need about half a kilogram of worms to process, while two to three people might need one kilogram of worms in a bin.

Obtaining the worms can be a challenge. The easiest way is to purchase worms from a worm farming operation. The Resources section contains a short list of suppliers of worms and worm farming equipment. Another possibility is to capture worms ‘in the wild’.

Keep in mind that even if you successfully manage to catch enough worms to set up a viable bin, it is quite likely that they won’t be the red wriggler type. Other species exhibit different behaviour, and may require different conditions and have different appetites than red wrigglers. That doesn’t mean that no other worms will work, but that you will need to experiment a bit to figure out the best conditions for the specific species you manage to capture.

There are several different methods for capturing worms living in a patch of earth. The easiest is to lure them to the surface by creating damp, dark conditions, with or without bait. Choose a patch of ground—anywhere with some grass or rich earth should be fine—but keep in mind that this method will damage any grass in the immediate capture area by blocking its light source for several days.

Wet the chosen patch of ground, and also wet a piece of cardboard (or sheets of newspaper). The larger the piece of cardboard, the higher the chances of luring worms, but the more grass could be killed. Place the cardboard down on the ground, and ensure that it and the ground underneath remain continuously damp. The wetness is to trick the worms into thinking it is raining and therefore safe to come to the surface.

You can also bait the area under the cardboard with scraps for the worms. Choose bait that is not appetising to pests like ants or other insects. For example, coffee grounds, plant trimmings, ground egg shells or finely chopped hair. Avoid fruit and vegetables because they might attract unwanted pests.

When the covering is in place, regularly check underneath the cardboard for worms. Gently grab any that come up and place them in the bin. Only add as much food as the worms you have can handle. You can increase the amount as you increase their numbers and they reproduce naturally.

Bin Placement

You must place your worm bin where you can monitor and access it easily. Red wriggler worms are most comfortable at temperatures between 17^o and 22^o centigrade. An ideal place to keep your worm bin might be outdoors in a shady spot. The worms can withstand cooler temperatures, but they are likely to decrease their activity and feeding levels, so be aware and adjust their feed accordingly. The bin must be brought indoors and kept warm if the temperature drops below 4^o centigrade at any time.

Feed and Bedding

Your red wriggler worms need bedding in which to live. Bedding also forms part of their diet. Bedding can be made of leaves, straw or shredded paper. Leaves, and straw are good bedding materials and can be used on their own, or mixed 50/50 with shredded newspaper. Make sure that you do not use glossy or heavily coloured paper. Also mix in a few handfuls of sand or soil to the bedding. the worms ingest and store it in their gizzard to help with digestion. The Bedding should be damp but not soggy or wet. After you moisten the bedding initially, it is unlikely that you will need to repeat it as the natural decomposition process of the organic waste provides enough moisture.

It is usually enough to feed the worms two to three times a week depending on how quickly the organic waste or food scraps are processed. The smaller food scrapws are, the faster the worms will be able to process them into worm castings. You can speed the process up even further by storing the food scraps in an airtight container for a few days before adding them to your worm bin. This allows the food to begin to decompose and accumulate a surface buildup of microbes, which is what the worms actually eat. Add the organic waste to a different area of the worm bin each time (if the bin has a wide, flat shape) and always cover it with some bedding.

Organic waste to add to the worm bin:

• Fruit and vegetable scraps

• Coffee grounds and tea bags

• Plant trimmings

• Finely crushed egg shells

• Unprocessed hair (chopped finely so the worms do not become entangled)

Problem items you should NOT add to the worm bin:

• Meat and fish

• Dairy products

• Onions or garlic

• Oils and fats

• Sauces, dressings and vinegar

• Salts (If you use water softener, do not use this water in your bin.)

• Animal and human waste

The items in the problem list are not good for the worms or cause unpleasant smell as they decompose. Also, because of their acidity, limit the amount of coffee grounds, citrus fruit peels and tomatoes that you add to your worm bin. Adding crushed egg shells weekly will help to keep a balanced pH in your worm bin and give the worms the calcium they need to produce cocoons. Onions and garlic should also be limited due to their natural antibacterial properties.

A large number of compost worms eating kitchen scraps. Under normal circumstances, the worms must not be left uncovered and exposed to light in this manner except during feeding and harvesting.

Photo: Doug Beckers (CC-BY-SA 2.0)

Harvesting

You should be able to harvest your vermicompost approximately every three or four months. You will know that the compost is ready when it looks like a dark, crumbly soil. This finished vermicompost is mainly composed of worm castings and some partly decomposed organic materials. When there are a lot of worm castings with very little organic material in the bin then the castings must be harvested urgently. Large quantities of finished castings are harmful to the red wigglers’ health. , However, the castings are completely non-toxic for people and animals and can be safely handled with bare hands.

There are many ways to harvest worm castings. Two of those methods are the migration method and the tarp method.

Migration Method

This method is easy but slow. In the migration method you push the completed vermicompost to one side of the bin and add fresh bedding and organic waste to the other side. you can afford to wait for a bit, simply swipe the finished compost toward one side of the bin and add fresh bedding and lots of scraps to the other side. The worms in the bin will slowly move towards the fresh food source of food. This migration process usually takes about four weeks. Once all the worms have moved to the opposite end of the bin, you can then scoop out the finished product from the side the worms have vacated.

A similar process can also be done with two separate bins, in case the bins' shape does not allow for easy separation of one side from another (eg bucket bin). In this case, migration is vertical rather than horizontal. By adding thin layers of feed and bedding (less than 30 centimetres at a time) the finished castings slowly fill the bin up, with the worms inhabiting only the top layer of bedding. When one bin is full, a second bin, with a thin layer of bedding and feed inside it is placed on top of the full one. Over time, the worms migrate through holes in the bottom of the second bin and move in, leaving the first bin on the bottom full of finished castings and no worms after four weeks.

Tarp Method

The tarp method is more labour intensive than the migration method, but it can be done much quicker. In this method you spill the contents of your finished worm bin onto a big sheet of plastic, cloth or newspaper. This is best done outside. You then separate the worm castings into small piles and let the sun shine on top of them. The worms will burrow to the bottom of each pile to escape the sunlight, allowing you to scoop the vermicompost off the top of each pile. Continue to add more vermicompost onto each pile and scoop off the worm-free compost until all you have left isa small amount of castings and your worms. You then need to add fresh bedding and organic waste and return the worms to the bin.

The tarp method can also be used without spilling the contents of the bin out. You just remove the lid of the bin, gently mix the bedding and put it in direct sunlight for about an hour. The worms will burrow their way downward allowing you toskim the compost from the top of the bin. You repeat this process until you only have a thin layer of worms and castings left at which you can then add new bedding directly to the bin and continue with feeding.

Using the vertical migration method, the worms in the bottom bin will be on top of their castings in this manner (and thus motivated to leave). Placing the bottom side of a bin containing one layer of feed on top of them will cause them to migrate upwards, leaving the lower bin full of castings.

Photo: Sustainable Sanitation (CC-BY 2.0)

Curing and Application

After it has been harvested, the next step is curing or maturing the compost. Curing vermicompost, unlike thermophilic compost, is not necessarily compulsory. However, curing vermicompost gives time for the bacteria present in it to increase the bioavailability of certain plant nutrients. For vermicompost, curing is generally considered complete after the continually moist castings spend 2-3 months in a dark, ventilated area. However, this maturation process could feasibly be allowed to take place when the vermicompost is in use with a plant growing in it.

Using vermicompost

• Mix it with soil using one part of the vermicompost to 10 parts of soil, making a 10% mix. You can use more of the vermicompost but if you use more than two parts vermicompost to five parts soil (a 40% mix), you may do more harm than good.

• Use it in your vegetable gardens and flower beds by putting it between plants and gently work it into the soil.

• Add some of the compost to the bottom of the hole you have dug for transplanting.

• Spread it under your trees and shrubs to help them grow better

• Sprinkle it on your lawn for naturally healthy grass.

• Make a compost tea by adding roughly ¼ cup of vermicompost to two litres of water and let it sit for 24 hours. This solution can be used for watering plants and spraying on leaves.

Challenges and Solutions

The following is a list of common problems encountered when making vermicompost and how to deal with them.