Fertilize for 'green' green grass

The recipe for green grass and great looking plants is simple: water, good soil, fresh air and fertilizer.

Are you surprised I included fertilizer?

Some gardeners have stopped fertilizing because they think it's bad for the environment. And it can be. That's because not all of the fertilizer we apply goes to the roots of plants. Instead, some of it ends up in streams and lakes, where it reduces water quality by promoting the growth of weeds and algae.

In fact, fertilizer runoff was recognized as such a big problem that Minnesota banned the use of most phosphorus lawn fertilizers in 2004. The grass fertilizer you buy today, in most cases, doesn't contain phosphorus.

So, if fertilizer runoff is a problem, then not fertilizing solves that problem, right?

Wrong.

It seems logical to assume that if you don't fertilize, then nutrients won't run off of your lawn. But a lawn that doesn't receive any fertilizer tends to grow spotty and sparse and doesn't develop the strong roots that help hold the soil in place. Without those strong roots, rainwater can wash away the top layer of soil, which can be a pollutant in and of itself. So, as odd as it might seem, it benefits the environment if you feed your lawn the right amount.

Crunching the numbers

Here's how fertilizers work: The nutrients in most fertilizers include nitrogen, phosphorus and potassium. The amount of each of these nutrients is listed on the front of the bag or box. The first number indicates the percent of nitrogen, the second number is the percent phosphorus, the third is the percent of potassium.

A lawn fertilizer with the numbers 20-0-5 would have 20 percent nitrogen, no phosphorus and 5 percent potassium. The remaining 75 percent of the fertilizer would be made up of other ingredients, such as oxygen, carbon, hydrogen and calcium.

Most fertilizers are applied based on the amount of nitrogen they contain, since that is usually the nutrient that plants will use most of over the course of a year. And while there is no "magic number" for the best results, there are general recommendations. For gardens, a ratio of 5-1-2 (such as 10-2-4 or 15-3-6) should be good for most situations. For lawns, a ratio of 5-0-1 should work.

Look on the package to determine how much fertilizer to use. A typical rule of thumb is about 2 pounds of nitrogen per 1,000 square feet of space (an area 50 feet long by 20 feet wide) per year. So, if you were using a fertilizer with a mix of 20-0-5, that would mean that you would apply 10 pounds of the fertilizer to 1,000 square feet to deliver 2 pounds of nitrogen to that area.