Rodale Press, publisher of Organic Gardening magazine is located in Pennsylvania where steel mills abound. Having more experience with slag, Rodale advises the user to be alert to the fact that some contain little in the way of useful nutrients and/or may contain excessive amounts of sulfur. Large quantities of sulfur can acidify soil. Read the analysis on the label. Agriculturally useful slag has an average composition of 40 percent calcium and 5 percent magnesium. It must also be very finely ground to be effective. See also: Lime and Rock dust.
Beet wastes, like bagasse, are a residue of extracting sugar. They have commercial value as livestock feed and are sold as dry pulp in feed stores located near regions where sugar beets are grown. Their C/N is in the vicinity of 20:1 and they may contain high levels of potassium, reaching as much as 4 percent.
Brewery wastes. Both spent hops (dried flowers and leaves) and malt (sprouted barley and often other grains) are potent nutrient sources with low C/N ratios. Spent malt is especially potent because brewers extract all the starches and convert them to sugar, but consider the proteins as waste because proteins in the brew make it cloudy and opaque. Hops may be easier to get. Malt has uses as animal feed and may be contracted for by some local feedlot or farmer. These materials will be wet, heavy and frutily odoriferous (though not unpleasantly so) and you will want to incorporate them into your compost pile immediately.
Buckwheat hulls. Buckwheat is a grain grown in the northeastern United States and Canada. Adapted to poor, droughty soils, the crop is often grown as a green manure. The seeds are enclosed in a thin-walled, brown to black fibrous hulls that are removed at a groat mill. Buckwheat hulls are light, springy, and airy. They'll help fluff up a compost heap. Buckwheat hulls are popular as a mulch because they adsorb moisture easily, look attractive, and stay in place. Their C/N is high. Oat and rice hulls are similar products.
Canola meal. See: Cottonseed meal.
Castor pomace is pulp left after castor oil has been squeezed from castor bean seeds. Like other oil seed residues it is very high in nitrogen, rich in other plant nutrients, particularly phosphorus, Castor pomace may be available in the deep South; it makes a fine substitute for animal manure.
Citrus wastes may be available to gardeners living near industrial processors of orange, lemon, and grapefruit. In those regions, dried citrus pulp may also be available in feed stores. Dried orange skins contain about 3 percent phosphorus and 27 percent potassium. Lemons are a little higher in phosphorus but lower in potassium. Fruit culls would have a similar nutrient ratio on a dry weight basis, but they are largely water. Large quantities of culls could be useful to hydrate stubbornly dry materials like straw or sawdust.
Like other byproducts of industrial farming, citrus wastes may contain significant amounts of pesticide residues. The composting process will break down and eliminate most toxic organic residues, especially if the pile gets really hot through and through. (See also: _Leaves) _The effect of such high levels of potassium on the nutritional qualities of my food would also concern me if the compost I was making from these wastes were used for vegetable gardening.
Coffee grounds are nutrient-rich like other seed meals. Even after brewing they can contain up to 2 percent nitrogen, about 1/2 percent phosphorus and varying amounts of potassium usually well below 1 percent. Its C/N runs around 12:1. Coffee roasters and packers need to dispose of coffee chaff, similar in nutrient value to used grounds and may occasionally have a load of overly roasted beans.
Coffee grounds seem the earthworm's food of choice. In worm bins, used grounds are more vigorously devoured than any other substance. If slight odor is a consideration, especially if doing in-the-home vermicomposting, coffee grounds should be incorporated promptly into a pile to avoid the souring that results from vinegar-producing bacteria. Fermenting grounds may also attract harmless fruit flies. Paper filters used to make drip coffee may be put into the heap or worm box where they contribute to the bedding. See also: Paper.