CHARLESTON, W.Va. -- Now is the time to introduce slow-release fertilizer to your perennial beds. Test your soil (you can find a soil test kit at Green's Feed and Seed or at many other garden centers) and use it as a guide to selecting the one to use.
There are three numbers on every bag of fertilizer, and those numbers tell just what is in that bag. It's important to use the right one.
Abbreviated NPK, the numbers represent the percentage, by weight, of three major plant nutrients: nitrogen, phosphorus and potassium. For example, a fertilizer designated as 24-8-16 is 24 percent nitrogen, 8 percent phosphorus and 16 percent potassium.
Any additional ingredients will be listed on the side label. This may include other nutrients like calcium, magnesium, iron, micronutrients and even the percentage of organic matter.
Speaking of organics, they must specify which nutrient(s) is organic, and it must be identified as either synthetic and/or natural, by percentage. For example: 20 percent of nitrogen organic (6 percent synthetic, 14 percent organic). Everything in that bag marked "organic fertilizer" isn't necessarily all organic.
I searched the U.S. Department of Agriculture National Organic Program's website for what felt like an hour to find some sort of definition of an "organic" fertilizer, and possibly a list of accepted additives. I found there are several levels of "organic" and that some chemical fertilizer components can be included in small quantities. "Natural" means something else all together!
So what do the different nutrients do?
To promote growth in leaves, flowers, vegetable plants and grass: add nitrogen (N). It helps produce a darker green plant color by encouraging chlorophyll formation, and nitrogen is also a building block for plant protein.
To promote healthy root formation: add phosphate/ phosphorus (P). Phosphate helps flowering plants reach maturity earlier, increases the plant's flowering ability and increase the size of the blooms.
To promote fruit and vegetable formation: add potash/potassium (K). It strengthens the plant tissues, and is essential for photosynthesis. Potash also increases the plant's resistance to disease and increases the plant or tree's ability to survive the cold winter months.
Typically, for general use, get the fertilizer with the highest first number, with the highest percentage of nitrogen. If you want to toughen up your plants for better drought, disease or winter resistance, use a fertilizer with a high last number, containing more potassium.
Don't think more is better: applying too much fertilizer can burn your plants and lawn. Follow the instructions on the bag.
Don't correct the soil, correct the plants
Someone asked me how to correct her alkaline soil before she planted her perennial bed. Why fight nature? I suggest she pick native plants that adapt to her acid soil, such as Russian sage (Perovskia atriplicifolia), globe thistle (Ehinops giganteus) and Oriental poppy (Papaver orientale). But if she's still intent on changing her soil, I suggest she add iron sulfate or ammonium sulfate. Granular sulfate is cheap, but slow to work. It's a slow process to lower soil pH and can take several years, especially if your soil is heavy clay.