Soil Feeding Rates And Fertilizer Formula

A great deal of fuss is made about the feeding rates of various fertilizer formula. I have seen amateur rose growers, for example, all but come to blows in arguing whether a 6-10-7 was a better rose fertilizer than a 5-10-5 or a 4-12-4! Advocates of all three were vehement in their protests that only their ratios and rates of feeding would produce perfect roses.

I wish I could be that dogmatic with any degree of confidence in my recommendations. Where I can be dogmatic is in saying that there is no perfect general fertilizer formula. Within reason, any complete fertilizer will produce good roses and other plants if the grower uses enough, without going overboard. Soil is an amazing buffering agent and will accept many times the amount of fertilizer usually recommended - without injury to the plants.

I recall a vegetable garden I made many years ago. I had little time to devote, so the only answer was to have the soil preparation and fertilizing done for me. The handy man I hired was not too good at figures (particularly decimals) and skipped a place in his calculations, which resulted in the application of ten times as much 10-6-4 fertilizer as I had intended.

Fortunately, this was a complete fertilizer, not only in the big three of N, P, and K, but in the minor elements as well. To show how selective and discriminating plants are in their food uptake, I saw not one instance of over-feeding of any one element. True, the weed growth was phenomenal (this was the first time in my life I ever had to cut ragweed with an axe) but everything else grew on the same phenomenal scale. So long as food elements are in balance and are supplied in amounts sufficient for good growth, with no one ingredient lacking, plants can be depended upon to take what they need and leave the surplus unused.

This does not mean that the point cannot be reached where the soil will be saturated with excess soluble salts which will damage or kill the plants. It does mean that the soil, particularly when it is liberally supplied with organic matter, is capable of buffering tremendous overdoses, so that, within reason, an accidental overdose need not be a calamity.

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 fertilizer costs, 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.

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.