Tropical Gardening: Composting — little things count

Today is Father’s Day, it also is the official first day of the astronomical summer and the summer solstice, meaning the sun has reached its northern most position in the sky (at 6:39 a.m. for Hawaii Island).


Today is Father’s Day, it also is the official first day of the astronomical summer and the summer solstice, meaning the sun has reached its northern most position in the sky (at 6:39 a.m. for Hawaii Island).

Here in the Northern Hemisphere, the date also corresponds with our longest daylight (13 hours, 20 minutes) and shortest nights.

What better way to celebrate this trifecta than with a garden project you can use to support the love of gardening, make great use of the long day and do something that will benefit all of us in Hawaii.

The project that comes to mind is composting of our garden and kitchen organic waste to keep it out of our landfills and create something truly good and useful. Numerous variations can be employed, ranging from one initially started in the kitchen, one using earthworms and one that even uses maggots. Each has its own set of pros and cons, but all lead to the breakdown of organic matter to make nutrient rich compost.

Composting can be defined as the speeding up of the natural process of breaking down organic material through the use of microorganisms and invertebrates. By actively maintaining optimum conditions of moisture, aeration and temperature, the decomposition occurs at a quicker pace.

Pile composting is practiced by many gardeners and is an aerobic process, where oxygen-loving microorganisms and invertebrates work to break down plant materials. At its simplest, it is a pile of leaves, twigs, branches and other plant debris that practice little management of the degradation process. Decomposition time generally is long, but requires very little commitment of time and labor.

In contrast, hot composting is an active process where pile temperatures, moisture levels and constituent plant material are monitored to optimize the degradation process.

The carbon-to-nitrogen (C:N) ratio of the materials is carefully monitored. A proper C:N ratio should be in the neighborhood of 25-30:1. Carbon-rich plant materials are the brown dried plant material, while the wet, green materials are rich in nitrogen. Hence the rule of mixing of brown and green for best results in composting.

A simple rule for the amount of brown and green material to use is a volume based recipe, where one-fourth to half would be green material.

Vermiculture, or vermicomposting, is the process of using earthworms to digest plant matter to create worm castings, a nutrient-rich compost-like product.

Earthworms are voracious eaters and about 2,000 worms will eat a pound of plant material per week. Worms like moist but not too wet environments, aeration and darkness, so a loose-fitting cover is essential for best results. Red wiggler worms are used most often and are normally housed in a wooden or plastic container.

Bathtubs and other similar large containers have been used to house very large populations of worms. As long as they have food and the environment is to their liking, the worms will thrive and multiply.

Items they do not feed on are meat, fats, oils and citrus rinds. Overfeeding can lead to rotting of plant material and odors, causing the worms to crawl away.

Bokashi composting originated in Japan and is conducted as a two-part process used to break down any organic matter, including meat, fish, bones and cheese.

In the first part, anaerobic fermentation of the organic material is accomplished with the use of “effective microorganisms” (EM) prepared as an inoculant mixture with wheat bran and molasses. Normally, fermentation is conducted in a special bokashi container, but can be done in any airtight container. A 5-gallon bucket with a lid works well.

Inoculant is placed on the bottom of the container and a layer of food waste is layered in the bucket and more inoculant is spread over the top. This process repeats until the bucket is full, at which time it is set aside until the faint smell of vinegar/sourness develops in about 2-4 weeks.

Then, the content is buried in the garden for the second step, where all of the organic matter breaks down into compost via aerobic microorganisms. The contents also can be buried in your regular compost pile.

In Japan, the first step commonly is conducted in a bucket under the kitchen sink, with the second done in an outside pot.

One of the newest methods of composting uses the larva of the black solider fly (technically a maggot) to rapidly eat many different kinds of organic waste and convert it to nutrient-rich compost. The adult solider flies are familiar to many of us as the skinny, inch-long black fly on our window screens and house walls.

The most common food material used is kitchen scraps and leftovers.


The Biopod is a commercially available unit used for cultivating solider fly larva and to collect pupating larva. Oil, fat and citrus are to be avoided. Solider fly larva will consume raw and cooked meat, poultry and fish.

For more information on this and other gardening topics, visit the CTAHR electronic publication website at or visit any of the local Cooperative Extension Service offices around the Island. I can be reached at

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