Three decades of experimentation have led me to the following recipe for homemade organic fertilizer. I call it Complete Organic Fertilizer or COF. It should work well in most parts of the U.S., although factors such as clay-to-sand ratio of magnesium-to-calcium ratio can affect results. See my companion piece A Better Garden Fertilizer for a discussion of that and soil testing.
Organic Fertilizer Recipe
Measure all materials by volume — by the scoop, bucketful, jarful, or whatever container you want to use, as long as it's the same for each ingredient. Proportions can vary 10 percent either way and still produce the desired results. Mix uniformly:
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 seed meal.**
**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 seed meal 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 labeled 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 other seed meals in that it has only about two-thirds the amount of nitrogen the other seed meals offer. However, since oil seed meals are valued for their protein content, the usually lower price of copra meal correctly matches its lowered level of NPK. Copra meal still works good as fertilizer, although when using it you need to amend the recipe a bit: up it to 6 to 8 parts copra meal; 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 seed meal and they have good results using it as fertilizer; one man has used GM soybean meal 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.