Bay Weekly

Is Your Lawn Hurting the Bay?

By Dr. Francis Gouin

       Greenish brown water stained by algae flows into the Bay from a tributary surrounded by lush green lawns. Seeing that, as I did in a recent photo, tells me the algae bloom is the result of excess nitrogen running off or leaching into the water from the applications of lawn fertilizers.

      Nitrogen is the most soluble nutrient in lawn fertilizers. What is not absorbed by grass roots leaches down into the ground and finds its way into the Bay.

     Unless your lawn is Zoysia or Bermuda grass, you should not be applying any fertilizers in the spring. Zoysia and Bermuda grasses are exceptions because as warm-season grasses, their roots absorb nutrients only when soils are warm.

      Most lawns in the Bay area are a mixture of bluegrasses and fescues. These are cool-season grasses.  The roots of cool-season grasses absorb most of their nutrients when soil cools down in late summer and early fall. Thus the months of September and October are the proper time for applying fertilizer, always at the recommended rate. These months are also safer because, with the exception of hurricanes, they bring fewer heavy downpours.

       The fertilizer pollution problem is worsened by the fact that many spring-applied fertilizers are blended with weed killers. Lawn herbicides that control broadleaf weeds like dandelions are best applied in the spring. Thus weed and feed fertilizers are a bad combination for cool-season grasses. The combination should only be used for warm-season grasses like Zoysia.

      Only weed killers specific for the control of crabgrass need to be applied in the spring for cool-season grasses. The best time to apply these weed killers is when forsythias are dropping their petals. Generally seeds of crabgrass begin to germinate within two weeks following petal fall.

      Now is too late. Truth is, you may not need them at all.

      I have not fertilized my lawn for more than a decade. Neither have I applied any weed killers. My lawnmower is permanently set to cut grass at four and a half inches, and all of the clippings fall in place. Cut it tall and let it fall.

      By cutting the grass tall and letting the clippings fall, I have developed a dense turf that chokes out weeds. The dense tall grass allows clipping to remain moist longer so that they compost on site. Upon composting, they release nutrients and organic matter into the soil. The taller-growing blades promote deeper rooting, making the lawn more drought-tolerant. I do not believe in wasting water irrigating lawns.

      The only treatment my lawn receives is agricultural grade limestone applied according to soil test results.

     A Bay Weekly reader recently asked me if a mulching mower is better than a regular mower. My answer was yes, providing the cutting height is three inches or more. When he informed me that his cutting height was two inches, I told him he was accumulating thatch. Thatch — dry grass clippings that need to be removed every three to four years to maintain a healthy turf — is a common problem with warm-season grasses.