Creating a sustainable soil environment

All fertilizers are investments, but organic ones are more likely to give reliable returns. Fertilizers from natural sources release a wide spectrum of nutrients slowly and steadily over a period of years, as opposed to the quick-release action of conventional nitrogen fertilizers that can wash away in the first heavy rain.
Organic fertilizers are once-living materials that can include everything from alfalfa meal and manure to oak leaves and kelp. The rewards of using organic fertilizers are tangible: good yields, better plant health and intense flavors. (No wonder the last three White House chefs prepared meals with organic produce!)

The overall strategy of organic growing is to feed the soil—not just the plants—with generous amounts of compost, manure, and side dishes such as alfalfa meal, bone meal and rock phosphate. These natural substances are far more familiar and less destructive to soil organisms than conventional chemical fertilizers, whose concentrated ingredients result in subsurface boom-and-bust cycles. In a single wheelbarrow load of fertile soil, there are more organisms than people on Earth—and they’re an industrious lot.

Bacteria, fungi, centipedes, beetles, earthworms and other soil organisms produce vitamins and antibiotics that promote growth and control disease; knit together particles of organic matter to create well-draining soil; and release carbon dioxide to help plants form new tissue.

Good soil functions like a healthy immune system: As long as beneficial organisms receive a high-quality diet, they keep bad organisms in check. Overdoses of chemical fertilizers and a shortage of organic matter weakens plants, allowing pests to invade. When that happens, many gardeners often resort to pesticides.

A Well-Balanced Diet

To see if your soil needs a better diet, get it a checkup by sending a soil sample to the county extension office (the address and instructions are available at soiltestinglab.colostate.edu; the test costs $28). Or buy a simple test kit that measures nitrogen, phosphorus, potassium and pH levels. Nitrogen enhances green, leafy growth; phosphorus gives plants energy and supports flower and seed growth; potassium synthesizes protein and builds strong stems.

Generally, conventional fertilizers contain the “big three” nutrients—nitrogen, phosphorus and potassium—but rarely contain dozens of other trace elements that support growth and help prevent disease.

Colorado soils are particularly deficient in water-retaining organic matter and available nitrogen. They’re also high on the pH scale, an alkaline condition that many crops don’t like. Soil pH above 7.3 inhibits plant uptake of essential nutrients like phosphorus. Garden staples like lettuce, corn and peppers prefer a pH just below neutral (7 on the pH scale), while tomatoes, strawberries and potatoes prefer an even more acidic soil.

The good news is that soils high in organic matter can buffer pH extremes, effectively allowing for good yields, even if soil pH is on the high side. Adding a 2- to 4-inch compost layer to beds every year is a good practice (see mastercomposter.com/pile for complete information on composting). Adding peat moss, leaves, coffee grounds and pine needles can also lower pH levels slightly, but the most effective health food for high pH is elemental sulfur in quantities up to 10 pounds per 100 square feet, which is expensive unless bulk supplies are available.

Compost Can’t Do It All

Compost organisms perform a very valuable service by making naturally occurring nutrients available in the soil. But eventually those nutrients become depleted. To offset what is harvested from the garden, return composted garden residue to the soil, along with other composted goodies like food scraps, leaves and manure.

If you have space or time constraints, high-quality compost can be purchased at reasonable prices. Eko Compost, for example, performs well, because it has a low ratio of carbon (i.e., not too much sawdust) to nitrogen, which is supplied with materials like alfalfa meal and poultry manure.

Composting should be a key strategy in the organic garden, but for best results compost needs allies from other animal, vegetable and mineral sources that have higher concentrations of nutrients. Deep-rooted cover crops or “green manures” also make existing nutrients available, because they mine nutrients from below the root zone of most vegetables (cover-crop roots can extend down 6 feet or more). When crops such as winter rye, hairy vetch, crimson clover and alfalfa are turned under and decompose, they enrich the soil.