A Better Way to Fertilize Your Garden: Homemade Organic Fertilizer

Your crops will thrive with this organic soil-building plan.
June/July 2006
Organic fertilizer ingredients are less expensive when bought in bulk. The basic organic fertilizer ingredients are seed meal, agricultural lime, gypsum, dolomitic lime (or dolomite), kelp meal and bone meal, rock phosphate or high-phosphate guano.


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 fertilizing 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 (see "Chemical Cautions" below).
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."

Complete Organic Fertilizer

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 (keep reading for "Basic Organic Fertilizer Ingredients"). 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.

Applying COF

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 (see "Which Crops Need the Most," below). 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 seedmeal 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 seedmeal 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 Cautions

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 seedmeal 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 seedmeal 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 seedmeal, 1 part bonemeal 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.

Soil Testing

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.

Chemical Cautions

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.

The Quick and Easy Guide to Homemade Fertilizer

Organic Fertilizer Recipe  

Mix uniformly, in parts by volume: 4 parts seed meal
1/3 part ordinary agricultural lime, best finely ground
1/3 part gypsum (or double the agricultural lime)
1/3 part dolomitic lime

Plus, 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) 
1/2 level kitchen measuring teaspoonful (carefully measured) of ordinary washing borax per each four quarts of seedmeal.**

**Overdoses of boron can poison soil. The acceptable range for boron is not very wide. Too little and you get hollow hearts and brown centers on brassicas and potatoes. Too much and everything is stunted or dies. Measure carefully! Blend this material carefully and thoroughly into your COF before spreading it. If this precision seems daunting just don't bother.  

How Much to Use

Once a year (usually in spring), before planting crops, spread and dig in the following materials.

Low-Demand Vegetables: 1/4 inch layer of steer manure or finished compost
4 quarts COF/100 square feet.

Medium-Demand Vegetables:1/4 inch layer of steer manure or finished compost
4 to 6 quarts COF/100 sq. ft.

High-Demand Vegetables: 1/2 inch layer of steer manure or finished compost
4 to 6 quarts organic fertilizer mix/100 sq. ft.

These recommendations will excellently grow almost any low-, medium- or high-demand vegetable on all soil types, except heavy clay in all humid climates. In addition to these initial applications, side-dress seedmeal around medium- and high-demand crops every few weeks through the season; altogether, this extra fertilizer may equal the volume used in initial preparation. (Gardeners dealing with heavy clay soils should use the higher amounts of COF and in the first year, spread double the amount of organic matter — up to an inch-thick layer of compost or well decomposed manure — and dig it in to a shovel's depth. In subsequent years, apply the same quantity of manure or compost and fertilizer mix as for any other kind of soil.)

COF is potent, so use no more than recommended. Do not over apply because COF contains lime, and excessive liming can be harmful to soil. It can take many years to correct excesses of lime. You can double the amount of manure and compost I suggest, but increase it no more than that. If you think your vegetables aren't growing well enough, do not apply more manure or compost; try fixing it with COF. And if you're already using COF and still some vegetable species are not growing well to suit you, then you should consider doing a soil test to find out if some other nutrients are in deficit (or great excess) because COF does not provide significant amounts of what are termed minor nutrients: sulphur, zinc, iron, copper and manganese. I wish I could add these minerals to the routine COF but doing so could cause more problems for some than it cured for others.

Sacked steer manure is commonly heaped in front of stores in springtime at a relatively low price per bag. However, this material may contain semi-decomposed sawdust and usually has little fertilizing value. However, it does feed soil microbes and improves soil structure, which helps roots breathe. And it is not raw manure; it has been at least partially composted. It is useful if not overapplied.

Which Crops Need the Most Fertility

For thousands of years, home gardens received the best of the family's manures, and lots of them. They have been coddled for millennia. Consequently few vegetable crops thrive in ordinary soil. Low- and medium-demand vegetables become far more productive when grown in soil that has received the basic amount of COF and a bit of compost. High-demand vegetables are sensitive, delicate species and usually will not thrive unless grown in light, loose and always-moist soil that provides the highest level of nutrition.

Low-Demand Vegetables Jerusalem artichoke, arugula (rocket), beans, beets, burdock, carrots, chicory, collard greens, endive, escarole, fava beans, herbs (most kinds), kale, parsnip, peas, Southern peas, rabb (rapini), salsify, scorzonera, French sorrel, Swiss chard (silverbeet), turnip greens

Medium-Demand Vegetables Artichoke, basil, cilantro, sprouting broccoli, Brussels sprouts (late), cabbage (large, late), cutting celery, sweet corn, cucumbers, eggplant, garlic, giant kohlrabi, kohlrabi (autumn), lettuce, mustard greens (autumn), okra, potato onions, topsetting onions, parsley/root parsley, peppers (small-fruited), potatoes (sweet or "Irish"), pumpkin, radish (salad and winter), rutabaga, scallions, spinach (autumn), squash, tomatoes, turnips (autumn), watermelon, zucchini, asparagus

High-Demand Vegetables Italian broccoli, Brussels sprouts (early), Chinese cabbage, cabbage (small, early), cantaloupe/honeydew, cauliflower, celery/celeriac, Asian cucumbers, kohlrabi (spring), leeks, mustard greens (spring), bulbing onions, peppers (large-fruited), spinach (spring), turnips (spring)

About Organic Fertilizer Ingredients

Seed Meals are byproducts of making vegetable oil and are considered valuable animal feeds. They are made from soybeans, flaxseed, sunflower seeds, cotton seeds, canola seeds, etc. Different kinds are more readily available in different regions of the country. When chemically analyzed, most seed meals show similar nitrogen-phosphorus-potassium (NPK) content — about 6-3-2. Because seed meals are used mainly as animal feed and not as fertilizer, they are labelled with their protein content rather than NPK content. The rough rule is that 6.2 percent protein provides about 1 percent nitrogen, so if you have choices buy whichever type of seed meal gives you the largest amount of nitrogen for the least cost. Copra meal is the byproduct of making coconut oil. It differs from the otherseedmeals in that it has only about two-thirds the amount of nitrogen the other seedmeals offer. However, since oilseedmeals are valued for their protein content, the usually lower price of coprameal correctly matches its lowered level of NPK. Coprameal still works good as fertilizer, although when using it you need to amend the recipe a bit: up it to 6 to 8 parts coprameal; the other ingredients remain in the same proportions. Because copra-based COF is less potent, you spread it heavier — say 6-8 quarts COF per 100 square feet.

If you want to use seed meals that are free of genetic modification and grown without sewage sludge or pesticides, choose certified organic meals if you can find any and can afford the tariff. I have reports from users of GM seedmeal and they have good results using it as fertilizer; one man has used GM soybeanmeal to feed his worm farm over the past three years and the system is running well. Of course, to be really certain of safety, those worms should be fed to frogs for four generations. Seed meals are far less costly in 50-pound bags, which can be found at farm stores. Seed meals are stable and will store for years if kept dry and protected from pests in a metal garbage can or empty oil drum with a tight lid.

Lime is ground, natural rock containing large amounts of calcium. There are three types. Agricultural lime should be relatively pure calcium carbonate. Gypsum is calcium sulphate. Dolomite, or dolomitic lime, contains both calcium and magnesium carbonates, usually in more or less equal amounts. If you have to choose one of these three kinds, it probably should be ordinary agricultural lime, but most people get a better result using an equal mixture of the three types. These substances are not expensive if bought in large sacks from agricultural suppliers. (Do not use quicklime, burnt lime, hydrated lime or other chemically active "hot" limes.)

You probably have read many times that the acidity or pH of soil should be corrected by liming. I suggest that you forget all about pH. Liming for the purpose of adjusting soil pH is entirely unnecessary in an organic garden, If liming is overdone, the practice may lead to the entire collapse of the garden; I have seen soil test results from people who did this. In fact, the topic of soil pH is controversial. Someday I am going to take the shade of J.I. Rodale to task because he convinced Everybody Else that liming to adjust soil pH is a key concern. My conclusion on the subject is this: If a soil test shows your garden's pH is low and you are advised to apply lime to correct it — don't. Each year, just add COF and compost/manure as shown in "How Much to Use". Over time, the pH will correct itself. If your garden's pH tests as 6.0 to 6.75, considered the ideal range to have soil pH, use the full recommendation of COF anyway, because vegetables still need calcium and magnesium in the right balance as nutrients. If your soil pH tests 7.0 or higher, then the basic formula for COF may not suit your needs; in this case you need a full soil test. If you routinely garden with COF you won't need to apply additional lime to the garden. The mix is formulated so that, when used in the recommended amount, it automatically distributes about 50 pounds of lime per 1,000 square feet each year.

Bone Meal, Phosphate Rock or Guano (bat or bird manure) all serve to boost COF's phosphorus level, hard phosphate rock and guano usually are also rich in trace elements. Bone meal may be the easiest of the three to find at garden centers and is the most available form; it will give you the biggest immediate result. Colloidal soft rock phosphate is probably the most valuable and useful form of rock phosphate. It analyses at having less P than the hard rock phosphates, but the phosphorus in the soft form is far more available and it does not come with the liability hard rock phosphate has —carrying traces of fluorine and sometimes uranium as well.

Kelp Meal (dried seaweed) has become expensive, but one 50-pound sack will supply a 2,000-square-foot garden for several years. Kelp supplies more than just a complete range of trace minerals, it provides growth regulators and natural hormones that act like plant vitamins, increasing resistance to cold, frost and other stresses. Some rock dusts are 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 of Grass Valley, Calif.

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.