The Art Of Bespoke Composts
Compost gets a lot of respect these days, and rightly so; good compost truly can be ‘garden gold’. In Victorian times, when head gardeners oversaw a flock of helpers, composts were carefully blended to suit specific plants. Their semi-scientific approach could involve a wide range of base materials, from wood ashes and local oak leaves to bird guano hand-dug from lonely island bird colonies half a world away. (Now there’s a job to contemplate.)
When cheap labor vanished in the wake of world wars, gardens and their care both simplified. The rise of chemical fertilizers (developed to use post-war munitions ingredients) left compost far behind. Once considered the realm of cranks and crackpots, today, the art and science of composting has gained more credence than ever. Organic growers certainly know its value, as does the United States Environmental Protection Agency, which has publicly recognized the power of constructed composts to assist in disease control or suppression for both plants and animals.
Composts That Cure
Recent research has developed in several directions, from farm and garden uses to native plant propagation to recycling dead chickens and other farm animals into disease-free, nutrient-rich composts. The ability of certain composts to destroy pathogens has also been explored, leading to what are called tailored or bespoke composts that can combat specific plant diseases. Root rots rank high among crop disorders, annually destroying over ten percent of American field crops. Add wilts, mildews, molds and blights to the list and that loss creeps higher still. These same issues vex home gardeners as well, so it’s good to know that mature compost can reduce or eliminate these pathogens as well or better than toxic chemical “fixes”.
How? A well constructed, complex compost offers a lively blend of beneficial soil biota that can out-compete the pathogens by capturing a the lion’s share of local nutrients. Some beneficial soil micro-organisms also create natural antibiotics that target pathogens, while others still simply eat them. As well, certain soil dwellers somehow trigger usually inactive disease-resistant plant genes so plants become better able to defend themselves. And that’s just the beginning.
Tailor Made Composts
Researchers have learned that these natural disease-fighting qualities can be boosted by adding specific micro-organisms and/or their preferred nutrients to compost blends. When these finessed composts are used on disease-prone crops, growers need little or no additional pesticides, fungicides, or nematicides to keep crops healthy. Compost also boosts the soil’s ability to retain water, reducing irrigation needs and costs. That keeps irrigation water cleaner, reduces worker exposure to nasty chemicals, and results in less contaminated food with higher nutrient quality. Since chemical soil treatments like methyl bromide are costly in many ways, eliminating their use with an annual application of compost is a win-win.
Ohio State University’s Dr. Harry Hoitink has led the tailored compost revolution for decades. His carefully created composts have defeated Pythium and other root rots while boosting crop yields dramatically. Hoitink often works with commercial growers on huge scales, but much of his work can be applied to our own backyards. For instance, Hoitink advocates composting field crop “waste” and reapplying it to keep the nutrient cycle as closed as possible. Similarly, we can glean and recycle as much garden and kitchen detritus as possible to increase soil health and quality.
Quality & Quantity Count
In some cases, Hoitink’s tailored composts have doubled crop yields, party through disease suppression and partly through soil enrichment. While farmers may spread 40-70+ tons of compost per acre, gardeners can get similar results by spreading 3-6 cubic yards per 1,000 square feet of bed. Where soils are depleted, sandy, rocky, or clay based, apply 3-6 inches of compost annually, preferably half in early spring and half in autumn.
Quality counts for a great deal, naturally enough. It is especially important that compost be mature when applied, neither elderly and inert nor still raw and hot enough to burn tender plants and roots. Mature, complex compost can heal soil, nurture plants, and significantly bolster plants’ disease resistance to root rots, nematodes, and foliar disorders. Indeed, in Florida field tests led by Dr. Tom Obreza, rootknot nematode damage stopped literally on the line between compost-treated and untreated plots.
Compost For Bioremediation
If your property has run-off issues, compost can be your new best friend. Compost bioremediation can capture and retain stormwater and even heal soils contaminated with agricultural or industrial residues, thanks to its ability to degrade VOCs (volatile organic compounds). That’s because mature and cured compost is packed with lively biota that can capture and degrade or digest soil and water contaminants in water. Tailored composts can even consume soil, water and air contaminants, from pesticides and petroleum products to solvents, chlorinated hydrocarbons, wood-preserving chemicals, heavy metals, and even certain explosives.
In our own backyards, spreading a thick (8-12 inch) layer of hog fuel (rough, pre-composted wood waste) can start the remediation work. A shallow ditch filled with hog fuel will halt most water flow, but if the runoff volume is high, deeper ditches or swales may be needed. To complete the cleanup, redirect excess runoff into a rain garden top-mulched with mature compost.
Why It Works
The basic science behind soil and water remediation with mature compost is fairly simple. Fresh or “raw” organic material is nutrient rich, so both beneficials and pathogens thrive. Well fed beneficials don’t release natural antibiotics until food resources dwindle, so plant pathogens can cause more diseases without that natural check. Mature, cured compost offers fewer nutrients, so the beneficials pump out the antibiotics to keep competition down, which in turn keeps plants healthy. When the compost gets old or is used up, the balance shifts back to helping pathogens prosper and plant are again under attack. To keep the balance steadily in that middle ground, we can apply compost once or twice a year, depending on our soil and plant needs.
Amazingly, this whole shifting process is managed by biotic backchat. “We are learning that during this process, microorganisms communicate with their environment and to some extent with each other,” Hoitink noted in an interview with Gene Logsden. “We call it ‘quorum sensing.’ Pathogens interact with biocontrol agents by signaling each other through molecules. The more stable the organic matter, as long as it has not been stabilized to the humic acid form, the greater the interaction, or perhaps, the better the communication.”