hello, when I'm browsing around at some garden stores and look at their organic (as well as non-organic) fertz, i see some npk values such as 10-12-8, some 21-15-10, and some .5-.4-.2 etc... does this mean the 21-15-10 is, say, stronger than the 10-12-8?? and what about the .5-.4.-.2?? is this suppose to be a very weak fertilizer? i'd prefer something a bit more powerful.
Yes, higher number means more. Base which one you select and use on sampling and testing of your soil, as well as what kinds of plants are being fertilized.
so would purchasing with an npk value in decimals (this is how most organic ferts are if i remember correctly) be a very low, and almost useless??
Depends on how much needed to be applied to your soil, and what other benefits the product might provide. Some organic fertilizers are useful primarily for increasing the biological activity in the soil, or supplying some humus-forming materials - as when composted, screened manure is periodically spread over a lawn being fertilized with petrochemical fertilizers. Before being fertilized your soil starts out with its own combination of mineral elements in specific amounts. Depending somewhat on what plants are to be grown or assisted by fertilization there will be certain amounts of available nutrients you will want to develop and maintain in your soil. Fertilization without a soil test beforehand to get some idea of what the existing situation is can result in over-fertilization which produces unpleasant effects such as nutrient runoff into water systems and even poisoning of the soil. Products containing high amounts of phosphorus in particular seem to be prevalent. If applied to the point of producing a toxicity this very slowly leached mineral can really only be gotten rid of by digging out and replacing the soil in the garden beds. There's always a point beyond which more pepper spoils the flavor instead of enhancing it. You have to taste the dish to find out how much to add.
