Reading the “nutritional information” on a bag of fertilizer is not so mystifying because, thankfully, there are certain rules that the makers of fertilizer must follow when they label their products. Almost always there will be three numbers, separated by dashes, on the front label (for example, 5-5-10). These denote the three nutrients that are of primary importance to most gardeners – nitrogen (abbreviation N), phosphorus (P), and potassium (K) – and the percentage of the fertilizer that they make up.
These nutrients enrich plants in various ways, but generally speaking, nitrogen encourages the growth of foliage, phosphorus contributes to the roots and seeds, and potassium promotes overall health and vigor. A good rose or general garden fertilizer will contain an optimum blend of all three (this is known as a “complete” fertilizer).
However, there is no “one size fits all” type of fertilizer. This is due not only to the differing needs of various plants but also the soil conditions at any given time. Many people, unfortunately, never have their soil checked before they begin gardening. This can alleviate a lot of problems down the road. If the soil has too much alkalinity or acidity, then plants might not be able to assimilate certain nutrients even if they are present. Also, soil might have been already fertilized for years previous, leaving high levels of phosphorus and potassium; in which case, nitrogen would be the only fertilizer needed (specialized fertilizers, also called “incomplete”, exist for this reason).
However, assuming that the soil you will be growing in doesn’t need to be adjusted, you should begin by mixing a rose or general garden fertilizer into it prior to planting anything. Fertilizers applied to dry soils will typically burn plants’ surface feeder roots. Read the bag’s label carefully and only apply as directed; application times, amounts, and the conditions under which they should be used are all very specific and should be followed to the letter. Dry-type fertilizers can be tilled or spaded into the soil. The calibrated spreaders that are used to fertilize lawns also work in the garden (lawn fertilizers, however, are not good for garden plants). However you decide to do it, distribute the fertilizer evenly and water it in thoroughly after application.
Roses and many other annuals benefit from being fertilized once a month on average throughout their growing season. However, care should be taken when applying fertilizer to existing plants. It should be watered in where their feeder roots are located, which is generally the area beneath their drip line – the edge of their leaves. Be sure to spread dry fertilizer on the soil only, and keep it off plants’ leaves.
Organic fertilizers often have lower nutrient concentrations than synthetic ones, but they also contain nutrients that the others lack. It’s important to remember, also, that no kind of fertilizer can provide for all the needs of garden plants indefinitely. Nutrients not supplied will be depleted from the soil by plant use and leaching with water, over time. It’s a good idea to occasional supplement one’s fertilizer with organic matter such as manure or composted soil, to insure that a good balance is maintained.