This week I read an uplifting article in the newspaper about how Sydney chefs are enthusiastically embracing the composting of food waste from their kitchens, turning it into nutrients for their own vegetable patches or local community gardens. The restaurants are using a very sophisticated machine that can produce compost very quickly, but for the home gardener there are several low-cost ways to turn kitchen scraps into valuable organic matter to improve our soil and nourish plants. All soils need organic matter on a regular basis to remain healthy and well structured. Compost also makes a mild, long-lasting plant food, which is gradually delivered to plants as microorganisms in the soil continue to break it down into its basic elements in a plant-available form.
The simplest method is to add the scraps to an existing open compost heap, usually a bay contained by brick walls, chicken wire or wooden slats, along with other organic refuse from the garden. To feed the microorganisms that decompose waste matter, a compost heap needs a balance between nitrogen-rich contents (such as kitchen scraps, animal manure and lawn clippings) and carbon-rich materials (such as shredded shrub and perennial plant prunings, straw and dead leaves). Such a heap can be passive (just left to rot down, with occasional hosings to keep it moist enough - with the materials taking a long time to rot down) or active (the heap being turned over with a garden fork regularly to promote aeration, which in turn speeds up decomposition by the action of aerobic microbes, with compost being produced much more rapidly).
Alternatives to compost heaps can be the plastic, bottomless dome with a lid (a passive type of system; shown at the start of the blog) and the compost tumbler (an active system, comprising a drum mounted on a stand with a handle for turning, which is filled to capacity then turned daily for a few weeks to oxygenate the material). These enclosed receptacles are preferable if you have a problem with rodents or other creatures in your area seeking out the food scraps added to open heaps. Newer fixed models have an aerated core, which hastens decomposition.
Another enclosed system is the worm farm, of which there are various styles. For years, I used one with three vertically interlocking trays, each with a perforated base to enable worms to move between the levels, and a solid-based compartment at the bottom to collect excess moisture in the system, but I had let it lapse in recent times. A kind friend has recently replenished my old worm farm with a complete tray full of worms and castings so that it was up and running from day one, and thus able to deal with all the scraps from my kitchen immediately. Don't use earthworms from your garden in a worm farm, as they are slow growing and have a slow breeding cycle: use the worms sold specifically for a worm farm. If starting from scratch, use moist, homemade compost or cocopeat for their initial bedding.
It is best to chop up the scraps a bit for them - though this may seem like pandering to them, remember that worms have no teeth and have to turn their mouths inside out to enable a morsel of food to pass into their alimentary canal! They will pretty much eat anything that is chopped up, but citrus and onion peelings are usually recommended to be avoided, and meat, fish, bread and dairy scraps should not be given to them. My new worms, like my old ones, seem to have favourite foods, though, with a penchant for strawberry tops, squashed blueberries and Lady Grey teabags, and like naughty little children do not eat up their lovely green vegetable (scraps) straightaway - but eventually everything gets devoured.
The worms turn the scraps into castings, a rich, dark and granular material, in which minerals in the original material have been changed into a plant-available soluble form, and cellulose partially broken down. When the castings are excreted by the worms, bacteria are expelled with them that continue the process of breaking down the organic matter. In my previous worm-farming days, I used to 'harvest' the castings by separating the worms from the finished material (something they appeared neurotically reluctant to do themselves), but this time I am going to focus on collecting the worm 'tea' by occasionally pouring water through the system and collecting it from the bottom box to pour onto the garden. The worms have been given a couple of upended plastic plant pots in the bottom box, by which they can climb back up to the bedding levels if they accidentally get washed down from the upper layers. Newer models of worm farm than mine are apparently designed for easier harvesting of the castings.
Another method of dealing with food waste is the bokashi bucket, which can actually live right in your kitchen. Scraps are placed in a special container and sprinkled with a special dry mixture of bran and microorganisms that in effect ferments the waste, eliminating unpleasant odours. Once the bin is full, its contents can either be dug into the ground or added to an existing compost heap, where it will complete the breakdown process quickly. The juice that collects in the base of the bucket can be siphoned off and used in very diluted form to feed plants. The bokashi bucket can contain any sort of kitchen refuse, including meat, fish, dairy and bread. I haven't yet tried it but hope to soon.
I'd love to know your preferences for turning kitchen waste into nutrients for your garden!
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