TAKE YOUR CHOICE
You may think I am inconsistent in recommending that formulae be checked carefully to see that plant food units are being purchased at the lowest cost, then stating that not too much attention need be paid to the value of one formulae over another, providing they are
reasonably similar in analysis and seem suited to the use to be made of them. My reasoning is, however, sound.
In order to determine exactly which of two or more fertilizer formulae would better meet the needs of the flowers, vegetables, shrubs or fruits growing in the garden, you would have to: (1) make expensive soil analyses at intervals during the growing season, to see what is left from the nutrients you applied, and (2) run experiments to see whether variations in the fertilizer formulae would produce superior results at lower costs. In the end, all this bother might save you a dollar or two a year, but this saving would be offset several times over by the cost of the soil analysis. I feel that soil tests for gardening is like swallowing a camel but straining at a gnat.
Of course, the technically minded gardener who enjoys dotting his Is and crossing his Ts can't fully enjoy himself without soil tests. I just don't feel they are necessary or desirable for the "average" home gardener.
Incidentally, a generally overlooked point concerning organic fertilizers (other than urea or urea-form products) is their content of insoluble nitrogen. Unless all or almost all of the nitrogen in any organic product is insoluble in water, the product will not give the "slow-release" or slowly available nitrogen effect for which you purchased and applied it. Here, again, is a dandy reason for checking package labels-including the tiny print-before you buy.
The ideal fertilizer-one that is all things to all plants-probably never will be produced, either by nature or by science. But there are many chemical and organic fertilizer source materials which supply nutrients that will do a good job if properly used, especially in mixtures. The discussion of nitrogen fertilizer "burn" should clarify-and eliminate-the problem for all gardeners. Similarly helpful are the explanations of specific fertilizer elements, how plants utilize them, the meaning of the three numbers on a fertilizer bag, and ways to figure fertilizer costs.