Lately it has become fashionable to remineralize the earth with heavy applications of rock flours.  Unlike most fads and trends, this one is wise and should endure.  The best rocks to use are finely ground “basic” igneous rocks like basalts.  They are called basic as opposed to “acid” rocks because they are richer in calcium and magnesium with lesser quantities of potassium.  When soil forms from these materials it tends to not be acid.  Most basic igneous rocks also contain a wide range of trace mineral nutrients.  I have observed marked improvements in plant growth by incorporating ordinary basalt dust that I personally shoveled from below a conveyor belt roller at a local quarry where crushed rock was being prepared for road building.  Basalt dust was an unintentional byproduct.

Though highly mineralized rock dust may be a valuable soil amendment, its value must equal its cost.  Application rates of one or two tons per acre are minimal.  John Hamaker’s The Survival of Civilization suggests eight to ten tons per acre the first application and then one or two tons every few years thereafter.  This means the correct price for rock dust is similar to the price for agricultural lime; in my region that’s about $60 to $80 a ton in sacks.  Local farmers pay about $40 a ton in bulk, including spreading on your field by the seller.  A fifty-pound sack of rock dust should retail for about $2.  These days it probably costs several times that price, tending to keep rock dust a novelty item.

The activities of fungi and bacteria are the most potent forces making nutrients available to plants.  As useful as tilling rock powders into soil may be, the intense biological activity of the compost pile accelerates their availability.  And the presence of these minerals might well make a compost pile containing nutrient-deficient vegetation work faster and become better fertilizer.  Were the right types of rock dust available and cheap, I’d make it about 5 percent by volume of my heap, and equal that with rich soil.

Safflowerseed meal. See Cottonseed meal.

Sawdust contains virtually nothing but carbon.  In small quantities it is useful to fluff up compost piles and prevent compaction.  However this is only true of coarse material like that from sawmills or chain saws.  The fine saw dust from carpentry and cabinet work may compact and become airless.  See Paper for a discussion of lowering the fertilizing value of compost with high C/N materials.

Seaweed when freshly gathered is an extraordinary material for the compost pile.  Like most living things from the ocean seaweeds are rich in all of the trace minerals and contain significant amounts of the major nutrients, especially potassium, with lesser amounts of phosphorus and nitrogen.  Seaweeds enrich the heap, decompose very rapidly, and assist other materials to break down.  Though heavy and often awkward to gather and haul, if they are available, seaweeds should not be permitted to go to waste.