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A Menu of Organic Fertilizers

Harmony Garden 2011 

Gourmet Treats to Feed Your Soil 

All fertilizers are investments, but some are more likely to give you reliable returns. Fertilizers that come directly 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 nitrogen-obsessed fertilizers that can wash away in the first heavy rain. If you choose to become an organic grower, you’ll inevitably become a broker in a stock market of materials that were once living, from alfalfa meal to manure to oak leaves. Your rewards are tangible: good yields, better health, and better flavor. (No wonder the last three White House chefs have cooked with organic produce.)

The overall strategy of organic growing is to feed the soil – not just the plants – with generous supplies of compost, manure, and side dishes such as alfalfa meal, bone meal, and rock phosphate – substances far more familiar and less destructive to soil organisms than concentrates that result in sub-surface boom and bust cycles. In a single wheelbarrow of fertile soil, there are more organisms than there are people on Earth, and they are an industrious lot! Organisms including bacteria, fungi, centipedes, beetles, and earthworms produce vitamins and antibiotics that promote growth and control disease; knit particles of organic matter together to create well-draining soil; and release carbon dioxide to help plants form new plant tissue. Good soil functions like an immune system; as long as beneficial organisms receive a high-quality diet they keep bad organisms in check.  But when overdoses of chemical fertilizers or a shortage of organic matter weaken the plants, the villains come after our plants. Soon enough, many growers then resort to pesticides.

A Well-Balanced Diet 

To find out if your garden soil needs a better diet, give it a check-up by sending a soil sample to your County Extension office. Or buy a simple test kit that will show levels of the basics: nitrogen, phosphorus, potassium, and pH. In general, conventional fertilizers contain the “big three” nutrients – nitrogen, phosphorous, and potassium – but rarely contain dozens of other trace elements that support growth and prevent disease.  Standard garden crops like lettuce, corn and peppers prefer a pH just below neutral - 7 - while tomatoes, strawberries, and potatoes like an even more acid soil. If the pH level climbs above 7.3 as it sometimes does in my Colorado garden, it inhibits plant uptake of essential nutrients such as phosphorus.

The good news is that soils high in organic matter can buffer pH extremes at both ends of the scale. Adding peat moss, leaves, coffee grounds, and pine needles can lower pH levels slightly, but the most effective health food for high pH is elemental sulfur in quantities that are expensive unless bulk supplies are available: up to 10 pounds per 100 square feet. For soils that are low in pH, crushed limestone is a good remedy.

Compost Can’t Do It All 

The organisms in compost make naturally occurring nutrients in the soil available – a very valuable service - but eventually those background nutrients become depleted. To offset what’s coming out of the garden, garden residues should be returned to the soil along with other goodies from the compost pile such as food scraps, leaves, and manure. If there are space or time constraints, high-quality compost mixes can also be purchased at reasonable prices. For example, Eko Compost performs well because it has a low ratio of carbon (e.g., not too much sawdust) to nitrogen (supplied with materials like alfalfa meal and poultry manure). While composting should be a key strategy in any organic garden, 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” can also make existing nutrients available because they mine nutrients from below the root zone of most vegetables (their roots go down six feet or more). When crops such as winter rye, crimson clover and alfalfa are turned under and decompose, they enrich the soil with these scavenged treasures.

Nitrogen enhances green, leafy growth; phosphorous gives plants energy and supports flower and seed growth; and potassium synthesizes protein and builds strong stems. Compost and manure supply moderate amounts of these nutrients, but manure can also supply excess saltiness and weed seeds, and imbalanced nutrients. Among the manures that are most useful are poultry, rabbit, alpaca, and cow manure.  A good product for higher pH 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 1-2 inches of soil. Master grower John Jeavons, whose biointensive gardening methods are now practiced all over the world, suggests the following formulas to maintain soil fertility:

Pounds of Fertilizer per 100 Square Feet, GOOD SOIL  

           Nitrogen (N)                               Phosphorous (P)                       Potassium (K)      

            .75 lb. blood meal or                1 lb. bone meal or                1.5 lbs. crushed granite or            

            4.2 lbs. alfalfa or                        2 lbs. phosphate rock         1.25 lbs of kelp meal or

               1 lb. fish meal                          or soft phosphate                1.25 lbs. of greensand


Pounds of Fertilizer per 100 Square Feet, AVERAGE SOIL  

                       Nitrogen (N)                  Phosphorous (P)                        Potassium (K)         

        2.25 lbs. blood meal or         2 lbs. bone meal or                    4.5 lbs. crushed granite   

        12.6 lbs. alfalfa meal or        4 lbs. phosphate rock                 or 4 lbs. of kelp meal   

          3 lbs. fish meal                                                                    or 4 lbs. of greensand  

These whole-food fertilizers are not cheap, but like organic food, they provide more overall value than their processed, synthetic substitutes. In general, the more you buy, the less expensive they will be. Some growers join fertilizer buying co-ops and order by the palette (typically forty 50-pound bags), shipped by truck or rail.  Products like alfalfa meal, cottonseed meal (order organic, because conventional cotton is heavily sprayed), fish meal, and kelp 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 fifty-pound bag. By knowing the soil-building values of various materials, you can substitute one for another.  I’ve had good results using coffee grounds in large quantities (from a local roasting factory) to supply nitrogen and lower pH; and alpaca manure for nitrogen and organic matter, both brought home in a borrowed pick-up truck.

To be a good organic gardener is to be a shrewd manager. You’re not just a garden geek, you’re a CEO with quintillions of employees in the soil. The goal is huge pumpkins and juicy tomatoes, and the best strategy to meet that mission is to keep feeding the soil.

Selected Sources of Organic Fertilizer 

David Wann coordinates Harmony Community Garden in Golden. He’s author of ten books, including The Zen of Gardening, Affluenza, and The New Normal. Find out more at