Vermicasting 101

Food scraps can be processed through earthworms into a rich fertilizer, which is called vermicasting. Earthworm casts (vermicast) is a nutritious organic fertilizer for houseplants too. A vermicasting system can be sized to process the daily food scraps of small or large households, and be set up indoors, outdoors or on a balcony. If designed around the earthworms’ feeding requirements vermicasting does not produce odor nor flies. Insulation during winter, and a reflective surface in summer might be needed since earthworms can survive at temperatures between 0 and 35 degrees Celsius. They perform best at room temperature (25 degrees Celsius).

Food scraps can be processed through earthworms into a rich fertilizer, which is called vermicasting. Red Wigglers or Eisenia foetida are the worm of choice for processing waste. The biology of earthworms and their feeding requirements are summarized in an OMAFRA factsheet on vermicasting. The ideal feed of red wigglers earthworms (Eisenia Foetida) is a biodegradable waste mix with a carbon to nitrogen (C/N) ratio of 25, a bulk density of less than 640 g / L, and 75% moisture. Earthworms do not tolerate high salinity levels, which is why materials like broilers waste needs to be pre-composted, and compost amended with NPK shouldn’t be used in the mixture.
Acidity should also be kept low, which is why dairy, eggs, meat and fruits need to be limited of less than 20% of the mixture volume. Detergents and other toxins need to be avoided. The UFO application Optimal Feed Mix (download) allows you to adjust the recipe of a feed mixture, to give it the right properties. This adjustment is done without inflating the mixture volume.

Based on published research (summarized in the OMAFRA factsheet on vermicasting), earthworms also need to absorb both oxygen and water through their skin to survive. This is achieved by placing them and their medium in a porous 5-sided container. A container made of 4mm screen walls will allow needed air in and excess water out, to keep the earthworms in optimal living conditions. They are also sensitive to all light waves except the color blue. This is why the porous container needs to be encased in a light-tight outer container, to allow earthworms to safely reach for the waste at the surface. They do not tolerate alcohol nor heat, so to prevent waste from fermenting, or heating up, the waste layer (and the container height) needs to be 30 cm or less. Earthworms can eat 75% of their weight. Knowing the waste production rate allows you to calculate the right quantity of earthworms for the bin so that the waste you add is consumed on a daily basis. Worms do not perform well if they are crowded, so enough of a medium should be used to keep them at a density close to 150 worms / litre. The Earthworm Bin Calculator (download) generates the dimensions of a 2 bin-vermicasting system, that meets the feeding and living needs of red wigglers. A 2 bin system is used so that after 15 days out of 30 days cycle waste is added to a second bin, which attracts earthworms out of the first bin and separates them from the finished vermicast. The finished product is a rich fertilizer ready to safely use on plants. It bulk density os between 0.6 and 1 kg per litre. When it is 2 weeks of age, most of the ammonium in this material turns to nitrate, the plant’s favorite form of nitrogen and the level of beneficial microbes increases in it. Even when fresh however, vermicast does not have high levels of salts, which makes it safe to use on plants.

Here are some best practices guidelines on how to store finished vermicast.

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