 Garden centers carry many different fertilizers in boxes, bags, bottles and tubs, and they all have a different application schedule. It is all very complicated and discouraging. There is one for roses, one for evergreens, one for flowering shrubs, one for tomatoes . . . we could go on forever. Fanatical gardeners will buy each kind of fertilizer, will use it properly, and will probably have a very nice garden. Unless they are very careful they might over-fertilize, which can damage plants as much as under-fertilizing. They will also spend money needlessly, and will be guilty of adding to the environmentally damaging quantities of nitrogen and phosphates in our soil and waters. Our bottom-line advice on fertilizing is: less is more. The Reluctant Gardener, who has been conscientiously composting, need only apply light applications of fertilizer.
A Simple Fertilizing Program Organically derived fertilizers are, of course, best. Buy a product that states its organic origins on the bag. We prefer to use good quality, organically derived, all-purpose 20-20-20 or 10-10-10 granular fertilizer. (An all-purpose 15-30-15 water-soluble fertilizer will also do the job, but it tends to be a little more of a nuisance to apply.) All fertilizers must be applied to moist soil, never to dry. During late May or early June, apply it at half-strength (that is, half what is recommended on the bag) on flowerbeds and around shrubs. In late-July or early August, do the same again. That's all. Use a spreader on the lawn, which is fertilized only in September. For shrubs or plants, sprinkle fertilizer around by hand (wear a glove, because some elements in the fertilizer can dry out your skin). Sprinkle thinly covering the root area, but avoid sprinkling it on leaves, because the fertilizer will burn them. Combined with a program of organic soil enrichment, this is all that is needed. This may sound stingy, but in the last few decades everyone has become accustomed to using far more fertilizer than is necessary. It is important that shrubs and roses not be fertilized after August 15. A late fertilizing would provoke a rush of soft new growth that will die under the first frost, weakening the plant and wasting money and effort.
THOSE THREE NUMBERS ON THE FERTILIZER The numbers you see on fertilizer bags are percentages of the three major plant nutrient groups. 20-20-20 means that the mixture is 20% nitrogen (N), 20% phosphorous (P) and 20% potassium (K). The other 40% is inert filler, which is why 20-20-20 costs more than 5-5-5 (which would be 85% filler). An oversimplified breakdown of what does what is this: nitrogen boosts leaf growth, phosphorous, root growth, and potassium, flower development. A mnemonic to remember this by is Little Red Flowers, Leaf-Root-Flowers. So if you wanted to green-up yellowish leaves you would buy a high nitrogen fertilizer, 20-5-5. To boost flower production on an unwilling annual, give it a 5-5-20. However, if you follow a good program of organic amendments and light, all-purpose fertilizing, it is unlikely the additional fertilizing will be needed.
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