Fertilizer may help lawn, but it hurts water

Dr. Sally Hornor
The Capital, April 12, 2008

Now that spring is here, we might feel the urge to go out and fertilize our lawns, hoping for that lush green carpet of summer. Let's consider for a moment the true cost of that lawn. First, there is the personal cost of fertilizer and the time required to put it down or the expense of hiring a professional to do it for you. As summer progresses, there is the cost, in both time and cash, of constant watering and mowing all that grass that was stimulated to grow by spring fertilizer or the cost of hiring someone to do that for you also.

Now let's consider the larger cost of fertilizing your lawn: the cost it has on our environment. Much of the fertilizer we apply to suburban lawns is washed off our yards and flows into storm drains. From there it enters our creeks, rivers and eventually the Chesapeake Bay.

Fertilizer meant to grow grass is equally effective at growing algae. Algae will grow at the expense of submerged bay grasses because algae are very efficient at taking up nutrients. We can see this effect quite clearly, especially along the waterfront where green lawn meets bulkhead or riprap. There is often a green fringe that extends 5 to 10 feet out into the water where algae grow in response to the nutrients that flow from that sloping lawn into the river.

We all know what happens once algal blooms proliferate. We know that they block the sun so that submerged grasses can't grow, and when they die over the course of the summer, they sink to the bottom of the river where they are then decomposed by bacteria and fungi. Decomposition takes up oxygen, and eventually the oxygen supply in the river is so low that all life in the river, except the bacteria, either leaves or dies.

In 2007, we had more fish kills in Anne Arundel County because of low oxygen than we have ever had in one year. And we had more blooms of toxic algae than we have ever had. Remember the report we heard last week from the University of Maryland Center for Environmental Science? Our county's rivers got a grade of D-.

Just because we refrain from fertilizing our lawns in the spring doesn't mean that we can't have a beautiful yard. Many yards in our area have soil that is so acidic that the nutrients that are there are not available to grass or other plants. Try adding lime to your lawn instead of fertilizer this spring. You might be surprised to see how nicely your yard greens up.

Probably the best activity we could undertake in our yards this spring, if we want to help turn around the condition of our rivers, is to convert some of our lawn to plantings of shrubs and perennials with mulch underneath. Not only does this add interest and beauty and wildlife habitat to our yards, but it helps hold stormwater on our property. Less stormwater flowing into storm drains and into creeks means clearer water throughout the summer.

We often hear about how each of us can make a difference. It's true. We all need to consider the larger cost of our actions before we start an activity that might damage our environment. Please reconsider adding fertilizer this spring.

Fall fertilizing is much less damaging to our creeks because excess nutrients washed into the creeks in the fall will result in cold water algal blooms. And though those fall and winter algal blooms will die and be decomposed, oxygen levels will not drop as low as they do in the summer because cold water holds much more oxygen than warm water does. Now that spring is here, let's go out and plant some shrubs.

Dr. Sally Hornor is a professor of biology at Anne Arundel Community College and a member of the Severn River Commission.

(Revised April 2008)