How to Make Homemade Vegetable Fertilizer From Materials That Work

Organic materials differ in how much of each nutrient they hold and how fast they release it. Colorado State's GardenNotes and Utah State give these typical values.

These are typical numbers, not label guarantees. University of Wisconsin's table lists bone meal at 1-15-0 and alfalfa at 3-0.5-3, and the nitrogen in manure varies widely with the animal and the bedding. A bagged product with a printed analysis is more predictable than a homemade one for exactly that reason.

Utah State draws the practical line. Fast-growing, high-demand crops such as sweet corn and potatoes do best with materials that release nutrients rapidly, while slow and very slow materials are good sources of organic matter but generally poor sources of nutrients.

The amount comes from nitrogen. Penn State advises basing any fertilizer amount on the nitrogen recommendation, because that is the way to avoid overapplying nitrogen. Colorado State's standard for a home vegetable garden is 0.2 pound of actual nitrogen per 100 square feet in a season, less where soil organic matter is higher.

Dividing the nitrogen needed by the material's nitrogen percentage, written as a decimal, gives the pounds of material. Oregon State's way of writing the same arithmetic is that 10 pounds of a 5 percent nitrogen material holds half a pound of nitrogen.

The blood meal answer lines up with Oregon State, which gives 1.5 to 2 pounds per 100 square feet. Colorado State's own table lists a higher product rate of 5 to 10 pounds, and it says plainly that those rates come from manufacturers and may over- or under-fertilize. The nitrogen arithmetic is the safer guide.

The alfalfa line shows why low-nitrogen materials are mainly soil builders. Ten pounds of meal for one small bed is a lot of material for a modest feed.

A homemade blend is then built from the soil test rather than from a fixed recipe. The nitrogen source covers nitrogen. Bone meal is added only if phosphorus tests low and the soil pH is below 7.0. A potassium source is added only if potassium tests low. Bed sizes and cup measures are in the vegetable fertilizer chart, and the fertilizer calculator runs the division for any percentage.

Organic nutrients are not available the day they go on. Colorado State explains that soil microorganisms have to convert them first, and that this activity needs soil warmer than 50°F with enough moisture. Cold or dry soil delays the release.

That shapes the timing in three ways. Slow materials such as feather meal and compost go in at bed prep or earlier, so they are releasing by the time roots reach them. Soybean meal goes in several weeks before sowing because it can inhibit seed germination. And early in a cool spring, Oregon State suggests a small amount of a more readily available nitrogen source, such as liquid fish or blood meal, while the slow materials catch up.

Compost and manure release over years rather than weeks. Colorado State estimates 5 to 25 percent of compost's nutrients and 30 to 50 percent of manure's become available in the first year, and Oregon State puts first-year nitrogen from poultry manure near 75 percent but from other manures at 25 to 50 percent. A bed that receives compost every year therefore builds up a reserve, and the yearly nitrogen need shrinks as organic matter rises.

Side-dresses later in the season call for the faster materials. The stage for each crop is in when to apply vegetable fertilizer.

Manure can carry bacteria such as Listeria, Salmonella and E. coli O157:H7, as well as roundworms and tapeworms, according to University of Maine Extension. The rules for using it on food crops come from the USDA National Organic Program and are repeated by extension services across the country.

Those intervals rule out spring manure for most vegetables, because most are ready to harvest in less than 90 to 120 days after spring planting. Iowa State's answer is to spread manure in fall, so the interval has passed by the time the next crop is picked, and not to apply it after the garden is planted.

"Aged" is not the same as composted. University of New Hampshire Extension warns that it is not safe to assume pathogens in an aged manure pile have been destroyed, because killing them takes sustained temperatures of about 131°F to 140°F for weeks, which home piles rarely reach. Commercially processed manure should say on the package whether it is pathogen-free.

Some manure never belongs in a vegetable garden. Cat, dog and pig manure carry parasites that are more likely to survive and infect people, and Maine, Iowa State and Penn State all say to keep them out of gardens and compost piles. Maine also advises that pregnant women, the elderly, very young children and people with health problems such as cancer, kidney failure, chronic liver disease or diabetes be most careful about eating uncooked vegetables from manured gardens.

Two common materials need limits rather than a ban.

Wood ash acts mainly as lime. University of New Hampshire Extension says it raises soil pH much faster than limestone, and that about 20 pounds per 1,000 square feet a year, one five-gallon pail, is safe for most garden areas. Iowa State gives the same limit and adds that ash should not be used where a soil test shows pH above 7.0. It does not belong around acid-loving plants such as blueberries, and Wisconsin notes that potatoes grown at higher pH are more prone to scab.

Grass clippings, hay, straw and manure can carry herbicide residue. NC State Extension identifies aminopyralid, clopyralid and picloram as the herbicides of concern, and notes that they pass through animals into manure and can stay active even after composting. Tomatoes, peppers, potatoes, beans, peas and lettuce are among the crops they damage.

Oregon State advises particular care with clippings from golf courses and commercial turf, and Minnesota warns against mulching vegetables with clippings from lawns recently treated for broadleaf weeds. When the source of compost or manure is unknown, NC State's test is to grow three pea or bean seeds in pots of a half-and-half mix with potting soil, beside pots of plain potting mix, and compare them after two to three weeks.

Several popular homemade fertilizers do not do what is claimed for them.

Eggshells do not prevent blossom-end rot. University of Minnesota Extension says so directly. Blossom-end rot is a calcium shortage inside the fruit, but most soils already hold plenty of calcium, and the shortage comes from a water-transport problem in the plant. Even where calcium is short, Minnesota notes that eggshells decompose too slowly to help, and Illinois Extension puts their breakdown at one to five years. Even soil moisture is the actual fix, covered in blossom-end rot on tomato.

Coffee grounds do not acidify soil. Minnesota says they feed soil organisms but do not lower pH, and Washington State found published pH values for grounds ranging from mildly acidic to somewhat alkaline. Washington State's Linda Chalker-Scott recommends keeping grounds to no more than 20 percent of a compost pile, and Illinois warns that a thick layer on the soil can repel water.

Banana peels have no tested rate. Extension experts answering through Ask Extension note that there are no scientific studies on banana peel fertilizer, and that the peels' potassium is wasted where the soil already has enough. The compost pile is the place they recommend.

Epsom salt helps only a magnesium shortage. Minnesota says it will not prevent blossom-end rot, and that too much magnesium can block calcium uptake and make the rot worse. It is worth using only when a soil test shows magnesium is low.

Eggshells, coffee grounds and banana peels still have value in the compost pile, where they add organic matter over time. They just do not replace a measured nitrogen source.