Creating a sustainable soil environment is crucial to growing vigorous plants. Here’s a guide to organic fertilizers that will help your soil become healthy.
Text and Photos by David Wann
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.
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.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!)
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.
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.
A Well-Balanced Diet
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.
Compost and manure supply moderate amounts of nitrogen, phosphorus and potassium, but manure can also provide excess salinity and weed seeds, and imbalanced nutrients. The most useful manures are poultry, rabbit, alpaca and cow. Michael Wade, of the Boulder-based seed company BBB Seed, swears by Moo Poo liquid fertilizer, which he orders in bulk from manuretea.com.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.
Boulder’s Harlequin’s Gardens, a nursery devoted to sustainable gardening practices, carries a full range of organic fertilizers. A good product for Colorado vegetable gardens is Yum Yum Mix, made from alfalfa meal, cottonseed meal, kelp meal, rock dust, Greensand and soft-rock phosphate. The recommended application rate is 1 cup per 3 square feet, or 4 pounds per 100 square feet, mixed into the top 1 to 2 inches of soil.
Master grower John Jeavons, whose biointensive gardening methods are now practiced worldwide, suggests the following formulas (in pounds of fertilizer per 100 square feet) to maintain soil fertility:
If a soil test determines you have average soil, apply apply nitrogen (N) in the form of 2.25 pounds blood meal, 12.6 pounds alfalfa meal or 3 pounds fish meal; phosphorus (P) in the form of 2 pounds bone meal or 4 pounds phosphate rock or soft-rock phosphate; and potassium (K) in the form of 4.5 pounds crushed granite, 4 pounds kelp meal or 4 pounds Greensand.
If the test determines you have good soil, apply nitrogen in the form of 0.75 pounds blood meal, 4.2 pounds alfalfa meal or 1 pound fish meal; phosphorus in the form of 1 pound bone meal or 2 pounds phosphate rock or soft-rock phospate; and potassium in the form of 1.5 pounds crushed granite, 1.25 pounds kelp meal or 1.25 pounds Greensand.
Once you learn the soil-building values of various materials, you can start to substitute one for another. I’ve had good results using coffee grounds—obtained from a local roasting factory—in large quantities to supply nitrogen and lower pH, as well as alpaca manure from a local farm for nitrogen and organic matter.“Whole-food” fertilizers are not cheap, but they provide better overall nutritional value than their processed, synthetic substitutes. In general, the more fertilizer you buy, the less expensive it will become. Some growers join fertilizer-buying co-ops and order by the pallet—typically forty 50-pound bags—shipped by truck or rail. Products like alfalfa meal, cottonseed meal (specify organic, because conventional cotton is heavily sprayed), fish meal and kelp meal can often be found at good prices in animal feed stores. In Colorado, alfalfa pellets are a good value at about $20 or less for a 50-pound bag.
To be a good organic gardener is to be a shrewd manager. You’re not just a gardener, you’re a CEO with quintillions of employees in the soil. The goal is huge pumpkins and juicy tomatoes, and the best way to achieve that is to keep feeding the soil—yum!
Here is a select list of organic fertilizers and the nutrients each supplies:
|Alfalfa meal||Supplies organic matter; high in nitrogen and potassium|
|Blood meal||High in nitrogen|
|Bluegrass hay||Good balance of nitrogen, phosphorus and potassium (NPK)|
|Bone meal||High in phosphorus; also good for nitrogen|
|Chicken manure||High in nitrogen and phosphorus|
|Coffee grounds/black tea leaves||High in nitrogen; lowers pH|
|Compost (homemade)||Moderate levels of NPK|
|Cottonseed meal||High in NPK|
|Cow manure||Good food for the beneficial soil organisms|
|Eggshells||High in calcium; good for nitrogen|
|Elemental sulfur||Lowers pH|
|Epsom salts||High in magnesium and sulfur|
|Fescue hay||Good balance of NPK|
|Fish meal||High in nitrogen and phosphorus|
|Granite meal||High in potassium|
|Greensand||High in potassium and trace minerals|
|Hairy vetch||Good winter cover crop that supplies nitrogen|
|Kelp meal||High in potassium; contains 60 trace elements|
|Oak leaves||High in potassium|
|Peat moss||Good for organic matter; slightly lowers pH|
|Pig manure||High in nitrogen|
|Rock phosphate||High in phosphorus|
|Sheep manure||High in nitrogen and potassium|
|Soybean meal||High in nitrogen|
|Worm castings||Contains 11 trace elements|
David Wann coordinates Harmony Community Garden in Golden, Colo. He is the author of 10 books, including The Zen of Gardening, Affluenza and The New Normal.