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The fertilizer aisle of the garden store might make you wish you'd paid attention in science class. But a basic understanding of fertilizer labels, along with some updated marketing by manufacturing companies, can ease the confusion.
"The gardener of today doesn't have to be … a chemist or a mad scientist to figure out each individual thing that they need for their garden,” says Oscar Fortis, head of new business development for Dr. Earth, a California-based company that sells organic fertilizers and soils.
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That's because many companies now package fertilizers based on how they will be used, labeling them for specific plants like tomatoes or azaleas, for example. But all fertilizers are based on a proportion of three basic elements, known as the NPK:
- nitrogen (N), to promote green growth
- phosphorus (P), for strong roots and blooms
- potassium, or potash (K), for overall health and structure
Somewhere on the package, because it's required by law, there will be the percentage by weight of each element. To use an example from the University of Maryland Extension, a 5-pound bag of 10-5-5 fertilizer contains .5 pounds of nitrogen, .25 pounds of phosphorus and .25 pounds of potassium. If you want a stronger lawn, you know to look for a higher proportion of nitrogen. For more blooms, pick a fertilizer with more phosphorus.
Organic fertilizers include manures, compost and bonemeal and come directly from plant or animal sources, according to the Oregon State University Extension Service. Inorganic fertilizers, such as ammonium sulfate or ammonium phosphate, are usually called commercial or synthetic fertilizers and go through a manufacturing process.
Before you put anything in your garden or on your lawn, however, first determine whether you even need fertilizer, experts say.