High-quality compost can make the difference between a so-so result and stunning success when growing in soil. Compost is now widely available in hydroponic stores, but how is a grower supposed to know the difference between one brand of compost and the next?
Compost is a bit like cheese. There are so many types of cheese in the world—from the kind that is made by skilled artisans following a traditional recipe just as generations of cheese makers have done before them, to the kind of mass-produced cheese-like product that comes in a spray can. These products are vastly different, but we use just one word to describe the whole range of products we call cheese. The same can be said about compost—there is such a wide variety of feedstocks and processes involved in its production and the end product can have major differences in appearance, smell, nutrient values and biology, but we still use just one generic name for it. We can check the ingredients listed on the bag, but that doesn’t tell us anything about the composting process—all compost is not created equal!
On a personal quest to find the highest expression of the art of compost making, I came across the traditional recipe for biodynamic compost. It comes from Rudolf Steiner, a philosopher/scientist who originated biodynamic agriculture in the 1920s.
At the heart of biodynamics is a deep respect for fertile, productive soil and the crucial role of compost in sustaining it. Steiner had some remarkable insights about how plants grow—to enhance the uptake of nutrients he provided a recipe for compost that has stood the test of time and has been proven by scientific research.
What’s so special about this recipe? Beginning with a simple base of organic dairy cow manure and straw, the biodynamic recipe requires six botanical ingredients, which are concentrated by specific alchemical processes during the course of a year before they are added to the pile. The six biodynamic preparations are yarrow, chamomile, nettle, oak bark, dandelion and valerian. Each of these relates to one or more plant nutrients and it is thought that the preparations act as catalysts to influence biological availability and nutrient uptake by plants. For example, nettle is linked to potassium, calcium, sulfur and iron, while valerian assists in the utilization of phosphorus.
Hydroponics has proven that plants can be grown under artificial conditions—but the plants are often stressed, which is the underlying cause of disease. Today, however, there is an increasing number of growers making a shift away from synthetic nutrients who are appreciating the simple beauty of working with natural processes within the soil—and they’re recognizing the benefits of using high-quality compost. Disease prevention can be achieved with high-quality compost because the massive numbers of beneficial microbes (good guys) it contains outnumber the disease-causing organisms (bad guys) so problems like powdery mildew tend to be suppressed. Not eliminated entirely, perhaps—but held in check to a level where they’re no longer a big issue.
‘Feed the soil and let the soil feed the plants.’ You’ve heard that before, but what does it mean when we say ‘feed the soil?’ What are we feeding it, exactly? Who’s hungry and what’s for dinner?
The answer is sweetly summed up in the soil food web diagram (see below). It shows a complex community of critters that is a whole ecosystem unto itself but is mostly invisible to the naked eye. This is a glimpse into the web of life forms that dwell in the skin of the earth and it’s also a diagram of a wild feeding frenzy combined with an orgy, going on 24/7. Plants have evolved with this web of interactions—with processes like the symbiotic relationship between themselves and fungi and especially the nutrient cycling that goes on whenever a microbe is swallowed by a predator and pooped out back into the soil. Gardeners of all levels of experience would be wise to explore this fascinating aspect of working with plants. “Start teaming with microbes, and get that biology into your soils and working for you”, say Jeff Lowenfels and Wayne Lewis in their popular book Teaming with Microbes: A Gardener’s Guide to the Soil Foodweb.
Always use the best-quality compost you can find. Make your first assessment with the compost testing tools you already possess—your eyes and nose. There are some obvious visual clues: there should be very few, if any, pieces of recognizable woody bits or other plant material, and you should look for the color of dark chocolate—about 70 per cent cocoa content. As far as smell goes, anything other than a pleasant, earthy smell is a bad sign. Your nose is giving you an early warning that something went astray in the composting process and that that particular compost doesn’t belong in your garden.
Compost is a fertilizer. It’s not standardized, so producers typically don’t list NPK on their bags. Growers still need to know what nutrients they’re getting in compost, though—and that’s where lab reports come in. Ask the manufacturer for a copy of the lab reports on their compost, both the nutrient analysis and the biological assay. In my opinion, any trustworthy company should be regularly producing these reports and they should be willing to share them with customers. If not, why not?
Compost is a biological inoculant. Good compost should be chock-full of a wide variety of microbes, along with the naturally-occurring foods they prefer. The humic acid you find in compost is far more biologically available than the humic acid you might obtain from mined substances like Leonardite.
Compost is also cost-effective. The organisms it contains provide priceless services. Bacteria store nutrients in their bodies—they are like tiny little packets of bioavailable fertilizer. This fertilizer then gets released back into the soil when the bacteria are consumed by predators like nematodes or protozoa. There’s really no need to entirely replace potting soil every year—simply rejuvenate it with high-quality compost. Ultimately the results will speak for themselves.
Compost teas and extracts essentially give your soil and plants many of the benefits of whole compost but in a liquid form. They also have the added advantage of containing a very high biomass of organisms if they’re made correctly. It’s absolutely essential to begin with high-quality compost when making actively aerated teas and extracts—and you might consider using more than one type of compost for your brews as well. Diversity is king!
When you go to the store for some cheese, you probably already know what type you want and how to recognize it. The same standards should apply when you’re buying compost—ask questions and know exactly what you’re buying. It’s up to you to know what’s going into your garden!
 “Effects of Biodynamic Preparations on Compost Development”, Carpenter-Boggs, Reganold, and Kennedy, in Biological Agriculture and Horticulture, volume 17, 2000.