Writer Steve Solomon developed his organic fertilizer mix after 30 years of research in his own superproductive gardens.
Photo By Muriel Brown (Chen)
My garden supplies about half of my family’s yearly food intake, so I do all I can to maximize my vegetables’ nutritional quality. Based on considerable research and more than 30 years of growing vegetables, I have formulated a homemade fertilizing mix that is beneficial for almost any food garden. This potent, correctly balanced fertilizing mix composed entirely of natural substances is less expensive than store-bought organic fertilizers, and it’s much better for your soil than harsh synthetic chemical mixes.
In my gardens, I use only this mix and regular additions of compost. Together they produce incredible results. I’ve recommended this system in the gardening books I’ve written over 20 years. Many readers have written me saying things like, “My garden has never grown so well; the plants have never been so large and healthy; the food never tasted so good.”
Why Not Cheap Chemicals?
Nonorganic synthetic fertilizers should come with labels warning against giving plants too much. One reason I don’t recommend the use of chemical fertilizers is that it’s too easy for inexperienced gardeners to cross the line between just enough and too much.
The nutrients in chemical fertilizers are too specific. This is particularly true of inexpensive chemical blends—even so-called “complete” chemical fertilizers are entirely incomplete. They supply only nitrogen, phosphorus and potassium. Especially troublesome is that chemical fertilizers rarely contain calcium or magnesium, which plants need in large amounts along with traces of several other minerals. Plants lacking essential nutrients are more easily attacked by insects and diseases, contain less nourishment and often don’t grow as well as they could.
Inexpensive chemical fertilizers have yet another drawback: They dissolve quickly. This usually results in a rapid burst of plant growth, followed by a big sag five or six weeks later, requiring another fertilizer application. Should it rain hard enough for a fair amount of water to pass through the soil, the chemicals dissolved in the soil water will leach, meaning they are transported as deeply into the earth as the water penetrates, so deep that the plant roots can’t reach them. With one heavy rain or one too-heavy watering, your fertile topsoil becomes infertile. The chemicals also can pollute groundwater. The risk of leaching is especially great in soils that contain little or no clay.
Organic fertilizers, manures and composts, on the other hand, release their nutrient content only as they decompose. As they are slowly broken down by the complex ecology of living creatures in the soil, they steadily release nutrients.
Some chemical fertilizers are “slow-release,” but these cost several times more than the type that dissolves rapidly. The seed meals in my organic fertilizer mix are natural slow-release fertilizers, and they usually are less expensive than slow-release chemical products.
Basic Ingredients for a Complete Organic Fertilizer
Seed meals, the byproducts of making vegetable oil from soybeans, flaxseeds, sunflowers, cotton seeds, canola and other plants, are one of the most important fertilizer ingredients. Different kinds are more readily available in different regions of the country. Because seed meals are used mainly as animal feed and not fertilizer, they are labeled by protein content rather than NPK (nitrogen, phosphorous and potassium—common fertilizer content labels), so buy whichever type gives you the largest amount of protein for the least cost.
If you want seed meals that are free of genetic modification and grown without sewage sludge or pesticides, choose certified organic meals. Seed meals are less expensive in 40- or 50-pound bags, which can be found at farm stores rather than garden centers; they will store for years if kept dry and protected from pests in a metal garbage can with a tight lid.
Lime, a ground rock containing large amounts of calcium, comes in three types. Agricultural lime is relatively pure calcium carbonate. Gypsum is calcium sulfate—sulfur is a vital plant nutrient that is deficient in some soils. Dolomite, or dolomitic lime, contains both calcium and magnesium carbonates. If you must choose only one kind, choose dolomite, but you’ll get a far better result using a mixture of the three types. These substances are not expensive if bought in large sacks. (Do not use quicklime, burnt lime, hydrated lime or other chemically active “hot” limes.)
Bone meal, phosphate rock or guano (bat or bird manure) all serve to boost the phosphorus level; phosphate and guano are usually also rich in trace elements. Bone meal will be the easiest of the three to find at garden centers, but they all add considerable fortitude to plants and increase the nutritional content of your vegetables.
Kelp meal (dried seaweed) has become expensive, but one large sack will last several years. Kelp supplies some things no other ingredient does: a complete range of trace minerals plus natural hormones that act like plant vitamins, increasing resistance to cold, frost and other stresses. Some rock dusts are also highly mineralized and contain a broad and complete range of minor plant nutrients. These may be substituted for kelp meal, but I believe kelp is best. If your garden center doesn’t carry kelp meal and can’t order it, you can get it from Peaceful Valley Farm Supply.
Quick and Easy Homemade Organic Fertilizer
To concoct this mix, measure all materials by volume: by the scoop or bucketful. Proportions that vary by 10 percent either way will be close enough to produce the desired results. I blend mine in a 20-quart plastic bucket, using an old saucepan as a measuring scoop.
Go as far down the recipe as you can afford, but if you can’t find the more exotic materials toward the bottom, don’t worry. However, if concerns about money stop you from obtaining kelp meal, rock dust or a phosphate supplement, I suggest considering these expenses a part of your health-care budget.
4 parts seed meal*
1/4 part ordinary agricultural lime, best finely ground
1/2 part agricultural lime (or 1/4 part gypsum)
1/2 part dolomitic lime
Add for best results:
1 part bone meal, rock phosphate or high-phosphate guano
1/2 to 1 part kelp meal (or 1 part basalt dust)
Applying the mix: Before planting each crop, or at least once a year (preferably in the spring), spread about a quart of fertilizer mix and 1/4 inch of finished compost evenly atop each 20 square feet of raised bed or planting row. Blend in fertilizer with a hoe or spade. This amount provides sufficient fertility for most garden vegetables. For higher-demand vegetables—asparagus, Brussels sprouts, cabbage, cantaloupe/honeydew, cauliflower, celery, kohlrabi, leeks, spinach and turnips—sprinkle small amounts of fertilizer around the root zones every few weeks. Gardeners with very heavy clay soils should use about 50 percent more fertilizer.
*For a more sustainable, less expensive option, substitute chemical-free grass clippings for the seed meal, although clippings will not provoke the same strong growth response. Use about a ½ -inch layer of fresh clippings, chopped into the top 2 inches of soil with a hoe. Then spread an additional 1-inch layer as a surface mulch.
Steve Solomon is the founder of Territorial Seed Company and has gardened extensively in California, Oregon, Canada and Australia, where he now lives. Solomon has written nine books on gardening and maintains an online gardening resource: soilandhealth.org. This article is adapted from his book, Gardening When it Counts.