By Clint Waltz
University of Georgia
From hard-core gardeners to novices, most people know you have to fertilize your plants to get the results you want. But reading a fertilizer bag can be intimidating if you don't understand what you're reading.
Most folks have heard of 10-10-10, but they may not know what the numbers stand for.
So what are the numbers?
They refer to the percentage of nitrogen (N), phosphate (P2O5) and potassium (K2O). So in a bag of 10-10-10, 10 percent of the weight of the bag is actual nitrogen, 10 percent is phosphate and 10 percent is potassium.
Knowing how much nitrogen is in a bag of fertilizer is fairly easy. The percentage is listed right on the bag. However, it's not as simple for phosphorus and potassium.
To determine the actual amount of phosphorus (P) and potassium (K) you have to do a little math. Use these formulas: P2O5 times 0.44 equals P, and K2O times 0.83 equals K.
A bag containing all three of these nutrients -- nitrogen, phosphate and potassium -- is considered a "complete" fertilizer. A product with any of these three missing is referred to as an "incomplete" fertilizer.
All plants need nutrients for proper growth and development. But various nutrients affect plants differently and are needed in varying amounts. All essential nutrients are required to sustain vigor so the plant can better resist environmental stresses, weeds, diseases, insects and other pests.
When it comes time to select a fertilizer, select a brand that includes these three primary nutrients.