Improving Your Compost
Improving your compost
By Darlene Belton, Master Gardener
Probably like you, I do backyard composting of kitchen scraps and yard waste. I have also almost completed Dr. Elaine Ingham’s Soil Food Web Foundation Program, an in-depth study of soil microbiology including how to produce Biocomplete™ compost. The program’s last section, which I haven’t finished yet, trains you to use a microscope to analyze soil and compost to verify whether the microbes present are beneficial or harmful to plants. I have yet to practise on the excellent microscope I’ve been loaned, but the program’s theory portion has already helped me improve my backyard ‘cold’ compost, even while I wait to have the yard space and time to practise producing ‘hot’ Biocomplete™ compost.
Compost is a fertilizer, but it works very differently than man-made inorganic fertilizers, which only succeed if the chemicals actually touch a plant’s roots; the residue is washed through subsoil and watersheds to harm downstream rivers and lakes. There are many benefits to compost, as a living mulch and organic matter-rich, water-retaining soil additive, but its greatest benefit is that it grows the bacteria and fungi that can partner with plants in a mutually beneficial nutrient exchange, the best plant growth and health-enhancer known. Then, these first-level microbes are consumed by microscopic predators such as protozoa and nematodes, and this initiates the self-sustaining system called the soil food web. Healthy, undisturbed soil already has a good food web, but with the disturbance we create in our gardens through digging and harvesting, every garden will benefit from the addition of good, living compost to replenish its food web. So, how can we improve the compost we produce?
Maintain aerobic conditions
This is probably the most important concern. Microbes are tightly adapted to specific conditions, such as different temperatures and amounts of oxygen. Most pathogenic microbes need anaerobic conditions to thrive and outcompete the ‘good’ microbes that support plant health. You know the ‘bad guys’ are winning when you smell that sour odour we all recognize. By ensuring your compost bins have good sized openings for air to penetrate and by turning the compost regularly you ensure that oxygen reaches all corners of your pile, which weakens or kills pathogens and allows ‘good’ microbes to proliferate. The fresh woodsy smell you inhale tells you that your little ‘good guys’ are winning! As one market gardener says, “If it smells good, it is good.”
Maintain moisture content
Microbes are unable to grow and function effectively in dry conditions, and ‘bad’ microbes win when it’s too wet, partly because this creates anaerobic conditions. So, like Goldilocks, aim for ‘just right’, or about 50 per cent moisture content. In the absence of a moisture meter, test by taking handfuls of compost from various places in your pile and squeeze in your hand. If a few drops appear between your fingers from a tight squeeze, this is a sign of about 50 per cent moisture.
Provide lots of food for fungi
Bacteria are very tiny, one-celled, not very mobile organisms that can only break down the simple sugars found in food waste and other ‘green’ compost material. Good bacteria are extremely useful in soil as they cluster around and even flow through plant roots for nutrient exchange, so you definitely want them in your compost, but they cannot provide plants with the incredible services provided by mycorrhizal fungi. Plants ‘ask’ these fungal partners to deliver specific needed nutrients by varying the sugar and protein content of their exudates. The fungi respond by dissolving the nutrients from rocks or by sourcing water, often at some distance, then transporting it all back to the plant through intricate mycelium networks. Scientists have much more to learn about this process, but what is being discovered now is mind-blowing.
The general composting recommendation is to add equal amounts by volume of ‘greens’ and ‘browns’, but although greens are needed to activate decomposition by feeding bacteria, it is the browns that provide fungal food (dried leaves, grass, wood chips, etc.). You can significantly multiply beneficial fungi by increasing the fungal to bacterial food ratio, especially by including lignin found in wood chips that only fungi can consume.
By increasing fungal food, you produce compost that supports the more complex needs of plants such as perennials, shrubs, and fruit trees that prefer a higher soil fungi to bacteria ratio. Plants in earlier stages of succession such as, first, weeds, and then annual vegetables and flowers, prefer a lower fungi to bacteria ratio. You can therefore roughly match the ratio to plant type, perhaps by having one bin for lower fungi to bacteria ratio and one for higher. However, because much damage occurs to fungal networks in human-intense landscapes, it is a challenge to help nature reach adequate beneficial fungi in our soils for our desired annuals, vegetables, and up the succession ladder. Saving leaf bags from fall through the following summer provides for an ongoing needed source of fungal food in cold compost bins.
One caveat: regular turning of compost to ensure proper aeration breaks up mycelia that has started to grow. Therefore, a rest period is recommended after your compost finishes actively working to allow fungi to recover, eat, and reproduce. The spores of mycorrhizal fungi will go dormant, maybe for years, until they come into close proximity with plant roots, so your compost is truly a ‘slow-release’ fertilizer.
Inoculate your compost
If you are composting in a typically depleted urban or rural setting, the soil beneath your pile is likely deficient in the rich, highly diverse mix of beneficial microbes needed to inoculate for the best compost. How to remedy this? Dr. Ingham suggests that you add a small amount of healthy soil sourced from an old growth forest located as near as possible to your home. Like native plants, microbes are adapted to their specific locales, such that if you introduce species from elsewhere, they either will be outcompeted by local species – and therefore be ineffective – or, much like invasive plants, they could upset the local ecosystem. You don’t need much forest soil, a snack bagful or even less, as the microbes will multiply rapidly in the rich food environment of your aerobically maintained compost.