Because my garden supplies about half of my family's yearly food intake, I do all I can to maximize my vegetables' nutritional quality. Based on considerable research and more than 30 years of vegetable growing, I have formulated a homemade garden fertilizer mix that works great in most food gardens. I call it Complete Organic Fertilizer, or COF. It is a potent, correctly balanced mixture composed entirely of natural substances. It's less expensive than similar commercially compounded organic fertilizers, and it's much better for your soil life than harsh synthetic chemical mixes.
The use of COF plus regular, minimal additions of compost has a long track record of producing incredible results. I've recommended this system in all the gardening books I've written over the past 20 years. Many of my readers have written back, 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."
To concoct COF measure out all materials by volume: that is, by the scoop, bucketful, jarful, etc. Proportions that vary by 10 percent either way will be close enough to produce the desired results. Making this formula by weight is more difficult and I suggest you do not try to. I blend my COF in a 20-quart plastic bucket, using an old one quart saucepan as a measuring scoop. I make 7 to 14 quarts of COF at a time.
At any cost of materials this mix is a good value when judged by the results it produces, but COF can be unnecessarily expensive unless you buy the ingredients in 50 pound sacks (20 kg) from appropriate vendors. Urban gardeners may have to do a bit of research to find rural suppliers. Farm and ranch stores as well as feed and grain dealers are the best sources for seed meals and kelp meal, which are typically used to feed livestock. If I were an urban gardener, I would visit the country every year or two to stock up. The other ingredients usually can be found at garden shops, although garden centers may sell them in smaller sized packages at relatively high unit prices. You also may find the these items on the Internet but they will be less costly from farm/ranch supply stores.
Seed meals and various kinds of lime are the most important ingredients (Read The Quick and Easy Guide to Homemade Organic Fertilizer for my basic fertilizer recipe). These alone will grow a great garden. Gypsum is the least essential type of lime, but it contains sulphur, a vital plant nutrient that is deficient in many soils. If gypsum should prove hard to find or seems too costly, don't worry too much about it — simply double the quantity of inexpensive agricultural lime. If you can afford only one bag of lime, in most circumstances your best choice would be ordinary agricultural limestone. The most fundamental nutrient ratio to get right in your soil is the balance of calcium to magnesium; it should be about 7 (calcium) to 1 (magnesium).To achieve that you could alternate agricultural lime and dolomite. First go through two bags of ordinary ag lime and then use one bag of dolomite lime. I strongly disagree with the many Rodale Press home gardening publications that insisted dolomite lime is the best single choice. Repeated use of dolomite has caused many organic gardens to become hard and compacted, making it seem that even more compost was needed than was actually required. Had the same soil had its magnesium to calcium ratio brought into proper balance, it would have loosened up by itself, seeming as though huge quantities of compost had been added.
Bone meal is usually available at garden centers. Guano, rock phosphate and kelp meal may seem too costly or too difficult to obtain, but they add considerable fortitude to the plants and increase the nutritional content of your vegetables. 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 too much. However, if concerns about money stop you from obtaining kelp meal, rock dust or a phosphate supplement, I suggest taking a hard look at your priorities. In my opinion, you can't spend too much money creating maximum nutrition in your food — a dollar spent here will save several in health care costs over the long term.
Once a year, best done immediately before planting the first spring crop, uniformly broadcast 4 to 6 quarts of COF atop each 100 square feet of raised bed, or, if you organize your garden in long rows, scatter 4-6 quarts of COF down each 50 feet of planting row in a band 12 to 18 inches wide. Blend in the fertilizer with a hoe or dig it in. This amount provides more than sufficient fertility for what I've classified as "low-demand" vegetables to grow to their maximum potential and is usually enough to adequately feed "medium-demand" vegetables. If you're planting in hills, first broadcast and dig in the usual 4-6 quarts of COF per 100 square feet and then mix an additional cup of fertilizer deep into each hill when forming it.
After the initial application, every three to four weeks you may sprinkle seed meal around medium- and high-demand vegetables. Spread it thinly, covering the area that the root system will grow into over the next few weeks. As the plants grow, repeat this "side-dressing," placing each dusting farther from the plants' centers. Each application will require more seed meal than the previous. As a rough guide, side-dress no more than 4 additional quarts total per 100 square feet of bed during a crop cycle. After side-dressing, if the growth rate fails to increase over the next few weeks, the most recent application wasn't needed, so don't add any more.
COF must not be spread more than one time each year or else you risk adding too much lime. The amount of lime in COF was carefully calculated to provide just enough calcium and magnesium and sulphur as essential plant nutrients but not enough to massively change the soil pH or overload your soil with calcium and magnesium. If you are planting a following crop in the same year and wish to increase fertility in that bed or row, if the earlier crop had already received the usual amount of COF do not use COF again until next year. Instead, spread and work in only seed meal at the rate of 3 to 4 quarts per 100 square feet. If you have lots of money and care about your health, a better supplemental fertilizer is three to four parts seed meal and one part kelp meal.
COF works great anywhere there is enough rainfall to grow crops well but it may not work well, may even do damage, if it is used in arid regions. That's because the soil mineral profile in much of the North American West and also in the Wheat Belt of the Prairie States, such as western Kanasas and eastern Colorado, is quite different compared to where there is more rain. Dry-climate soils tend to have high levels of calcium and sometimes excessive magnesium or sodium. Gardeners in those regions had better consult their local experts about what sorts of lime, if any, should be put into your soil. If, without doing a soil test first, I had to recommend a fertilizer for someone in these regions, I'd suggest digging in a half-inch-thick layer of compost or rotted manure, making a mixture of 4 parts seed meal, 1 part bone meal and 1 part kelp meal, spreading that incomplete organic fertilizer at 4 quarts per 100 square feet, and in that conversation I'd strongly urge the person to get a proper soil test.
People who have been compost gardening for many years are usually delighted when they experience what happens when they add COF. However, COF has limitations: it is designed to bring an imaginary soil containing absolutely no plant nutrients to near-perfection in terms of the major nutrients — NPKCaMg. Complete Organic Fertilizer contains some sulphur, but often this proves to be not enough sulphur. It does not provide the "minor nutrients" — copper, zinc, iron, manganese, boron. The kelp meal in it insures that your soil is not critically short of a long list of "trace nutrients" such as cobalt or iodine.
COF will, over three or four years of use, induce soil imbalances, especially amongst the minor nutrients. If everything that was taken from your garden were returned to it, then, assuming your soil was sufficiently well endowed from the beginning, it might never run short of minor nutrients. However, most of the minerals that plants remove end up in the septic tank or sewerage system. After a few years of this removal, even though you are using COF and adding major nutrients in approximately the correct amounts relative to each other, the soil might start moving seriously out of balance. In consequence you may begin to experience new problems — diseases usually. Or some species may not grow as well as it did a few years ago. I suggest that after using COF for three years, you have a full and proper soil test done and from its results work out your own custom COF. You might discover you have built too high a level of calcium and/or magnesium. In that case you can delete all limes — ag lime, dolomite lime and gypsum — from the mix. If you find you have a surplus of P (and I have seen several local gardens test that way), you can leave out the phosphorus booster from your own COF.
For soil testing I recommend Logan Labs because Logan's test method leads to full remineralization and better nutritional outcomes. And Logan is inexpensive. Ask for their Standard Soil Test. Logan's test results will not serve to guide an amateur; however, for a fee Logan will provide a soil prescription. If you did okay with high school chemistry, even if you hardly remember any of it, you will be able to work out your own custom COF with the help of a small book called The Ideal Soil written by Michael Astera. A copy can be purchased online at Soil Minerals.
Synthetic fertilizers and naturally occurring salts like sodium nitrate and potassium sulphate, should come with labels warning against giving plants too much. One or 2 cupfuls of these can be the maximum amount 100 square feet of soil can accept. But uniformly spreading only one or two cups of material over 100 square feet of soil is not easy to accomplish. That is one reason I don't recommend the use of chemical fertilizers. It is too easy for inexperienced gardeners to cross the line between just enough and too much.
Chemical fertilizers usually are too pure. This is particularly true of inexpensive chemical blends — so-called "complete" chemical fertilizers are entirely incomplete. They supply nitrogen, phosphorus and potassium. Some types also contain a useful amount of sulphur. However, unless the manufacturer intentionally puts in other essential minerals, the chemical mix won't supply them. Especially troublesome is that chemical fertilizers rarely contain calcium or magnesium, which plants need in large amounts. Crops also require significant quantities of minor nutrients such as zinc and copper. Plants short on any essential nutrient, major or minor, are more easily attacked by insects and diseases, contain less nourishment for you and often don't grow as well as they could.
There is yet another chemical drawback: Inexpensive chemical fertilizers dissolve quickly. In soils lacking clay this usually results in a rapid burst of plant growth, followed five or six weeks later by a big sag, requiring yet another application. Should it rain hard enough for a fair amount of water to pass through a clayless soil, most of the chemicals dissolved in the soil water will be transported as deeply into the earth as the water penetrates (this is called "leaching"), Often nutrients are leached so deeply that the plant's roots can't reach them. With one heavy rain or one too-heavy watering, your fertile sandy topsoil becomes infertile. The chemicals also can pollute groundwater.
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. Soil conditions determine the how long it takes to fully decompose. Complete decomposition of most organic fertilizers takes around two months in warm moist soil. During that entire time, they steadily release nutrients.
Chemical fertilizers can be made to be "slow-release," but these sorts cost several times as much as the type that dissolves rapidly in water. The seed meals in COF are natural slow-release fertilizers, and they usually are considerably less expensive than slow-release chemical products.
Adapted from Gardening When It Counts, a MOTHER EARTH NEWS "Book for Wiser Living," from New Society Publishers. The text and recipe presented here were updated by the author, Steve Solomon, in December 2011 to reflect new research and experience with COF.
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