There is a great deal of garden lore about kelp meal’s growth-stimulating and stress-fortifying properties.  Some garden-store brands tout these qualities and charge a very high price.  The best prices are found at feed dealers where kelp meal is considered a bulk commodity useful as an animal food supplement.

I’ve purchased kelp meal from Norway, Korea, and Canada.  There are probably other types from other places.  I don’t think there is a significant difference in the mineral content of one source compared to another.  I do not deny that there may be differences in how well the packers processing method preserved kelp’s multitude of beneficial complex organic chemicals that improve the growth and overall health of plants by functioning as growth stimulants, phytamins, and who knows what else.

Still, I prefer to buy by price, not by mystique, because, after gardening for over twenty years, garden writing for fifteen and being in the mail order garden seed business for seven I have been on the receiving end of countless amazing claims by touters of agricultural snake oils; after testing out dozens of such concoctions I tend to disbelieve mystic contentions of unique superiority.  See also:  Seaweed.

Leather dust is a waste product of tanneries, similar to hoof and horn meal or tankage.  It may or may not be contaminated with high levels of chromium, a substance used to tan suede.  If only vegetable-tanned leather is produced at the tannery in question, leather dust should be a fine soil amendment.  Some organic certification bureaucrats prohibit its use, perhaps rightly so in this case.

Leaves. Soil nutrients are dissolved by rain and leached from surface layers, transported to the subsoil, thence the ground water, and ultimately into the salty sea.  Trees have deep root systems, reaching far into the subsoil to bring plant nutrients back up, making them nature’s nutrient recycler.  Because they greatly increase soil fertility, J. Russell Smith called trees “great engines of production.”  Anyone who has not read his visionary book, Tree Crops, should.  Though written in 1929, this classic book is currently in print.

Once each year, leaves are available in large quantity, but aren’t the easiest material to compost.  Rich in minerals but low in nitrogen, they are generally slow to decompose and tend to pack into an airless mass.  However, if mixed with manure or other high-nitrogen amendment and enough firm material to prevent compaction, leaves rot as well as any other substance.  Running dry leaves through a shredder or grinding them with a lawnmower greatly accelerates their decomposition.  Of all the materials I’ve ever put through a garden grinder, dry leaves are the easiest and run the fastest.