“Feed the soil, not the plant.” I experienced this pivotal epiphany when my husband and I attended Plant Delights Nursery’s class, “The World of Soil.” For the first time I really got it that good dirt is alive, and – this is the really important part – the more alive the dirt, the healthier the plants are in it.
Shortly thereafter I read Teaming with Microbes: A Gardener’s Guide to the Soil Food Web by Jeff Lowenfels and Wayne Lewis, a layman’s guide to soil science. Lowenfels and Lewis illuminated the ecosystem of living soil in a powerful way. I became a true believer.
A History of Fertilizer
Before World War I, farmers everywhere used only composted manures, kitchen and garden wastes and seaweed to amend their fields, because that’s all there was. When hostilities ceased in 1918, armaments manufacturers faced severe profit cuts. They figured out that the same ingredients used to make firearms – nitrogen, phosphorus and potassium – also enhance crop performance. An aggressive marketing campaign launched the commercial fertilizer industry.
Crop yields rose dramatically, but so did pest problems and soil depletion. The new, “synthetic” plant foods came in the form of chemical salts, which had to break down in the presence of water before their nutrients became available to the plants. The salty byproducts of this reaction didn’t magically disappear from the soil, they accumulated. Exposure to salt causes soil microbiota to dehydrate and die. That’s why, once you start using synthetics, you have to keep on using them. Their mode of action essentially renders the fertilized soil sterile.
The Espoma Company’s Organic Traditions line of products includes single-element fertilizers as well as their familiar Plant-Tone, Holly-Tone and Rose-Tone, all with non-burning, low N-P-K numbers.
A Cautionary Tale
When I worked at a garden center, a customer once special-ordered 75 flats of centipede-grass plugs. Because the plugs looked a bit peaked on arrival, the owner asked another employee to sprinkle them with a little 8-0-24 fertilizer. The hapless girl spread an entire 50-pound bag on the 6 by 12 foot area. Even though we watered and watered, trying to leach the stuff out, the shock proved too much for the plugs. They all died from an extreme case of root burn.
This same death-by-fertilizer can happen in your own garden. Avoid it by learning to work with your soil instead of against it. Fertilizers labeled “organic” have dramatically lower N-P-K numbers than synthesized formulas. For example, compare Espoma’s Plant-Tone’s analysis is 5-3-3 to Osmocote’s 18-6-12. Lower numbers mean root and foliar burning are simply not possible.
In nature, fungi and bacteria consume and excrete nutrients in the soil. Protozoa, worms and arthropods consume and excrete the microbiota. Birds, reptiles, amphibians and small mammals consume and excrete the protozoa, worms and arthropods, in turn providing food for fungi and bacteria. This is the nutrient delivery system Mother Nature devised, devoid of human intervention. When you consider undisturbed habitats like forests, grasslands and rainforests, you have to admit Mother Nature knows what she’s doing.
We make a top-dress for our planting areas with generous helpings of a mixture of 1 16-ounce cup of kelp meal and 6 16-ounce cups of Holly-Tone to each 50-pound bag of Black Kow. (I opened the Holly-Tone from the bottom. Sorry.)
We can make our own gardens sustainable by replicating natural processes. The best way to do that is to treat your soil with annual topdressings of composted organic matter, either purchased or homemade. Incorporating compost into the soil improves drainage in heavy soils and increases moisture retention in sandy ones, but most importantly it attracts and feeds the bacteria and fungi at the base of the nutrient chain.
The three primary elements plants need to get out of the soil around them are nitrogen (N), phosphorus (P) and potassium (K). For a very simple explanation, nitrogen produces lush, green foliage; phosphorus, in the oxide form of P2O5 or phosphate, encourages blooming; and potassium, as potash or K2O, aids in growing healthy roots.
Also known as the “guaranteed analysis,” the three digits emblazoned on most fertilizer packages refer to the percentage by weight of each primary element per bag of mixture. For example, a 40-pound bag of 10-10-10 works out to 10 percent nitrogen, 10 percent phosphorus, 10 percent potassium and 70 percent of inert ingredients. In this particular case, the inert ingredients are 28 pounds of itty-bitty rocks.
Commercial fertilizers aren’t entirely counterproductive. Self-contained systems, like pots, benefit from their use. Most potting mixes are soilless, and therefore sterile, meaning there’s no microbiota to kill. Both houseplants and outdoor seasonal containers appreciate occasional applications of either granular or water-based nutrition. Whatever you use, always follow label directions. When it comes to fertilization, more is absolutely not better.
In my own garden, I trundle out the wheelbarrow every spring and combine 1 16-ounce cup kelp meal, 6 16-ounce cups of Holly-Tone (Plant-Tone if your soil is already acidic) and a 50-pound bag of Black Kow or other composted product. I distribute it liberally right on top of the mulch (mine is shredded leaves). Some may rake back their mulch first, but that’s too much work for me, I just go back and ruffle the mixture in with a garden claw. Either way, the idea is to get the composted material in contact with the soil.
The 2,700 square feet of planting space in my yard takes about 25 bags of Black Kow, or roughly one amended wheelbarrow load per 100 square feet. Come July, I usually toss around another dose of Plant-Tone and kelp, without the Black Kow, depending on the weather.
A New Mindset
Once you realize it’s the soil that needs feeding instead of the plants, understanding fertilizer becomes easier. By mimicking nature and limiting synthetic inputs, we become facilitators of the vital interconnectedness that living soil represents, to the better health of our plants, our planet and ourselves.
A version of this article appeared in a March/April 2014 print edition of State-by-State Gardening.
Photography courtesy of Jeffrey Heyden-Kaye (www.istockphoto.com/heydenkaye) and Kathy Fitgerald.