Growing Concerns: Fall is most important time to fertilize lawn

Yikes! Can you believe it’s almost Halloween? You’ve probably already stocked up on treats for the neighborhood kids. But have you treated your lawn to the care it needs to survive the cold, wet days ahead?

Don’t stop mowing just yet. Continue to mow until the grass stops growing. Don’t worry about mowing over that light sprinkling of autumn leaves. Shredded leaves add nutrients to the soil. As the leaves begin to drop in heavy drifts, rake them up and mix into the compost pile or mow over them with the bagging attachment. The chopped leaves will make a nice mulch for your garden beds.

In Western Washington, late fall is the most important time to fertilize the lawn. Grass, like other perennial plants in your garden, must have time to slow its growth and harden off before frosty weather sets in. As winter approaches, grass accelerates storage of nutrients in its roots. These are the nutrients that will help it green up and grow in spring.

Most full service nurseries now stock excellent organic, slow-release lawn fertilizers that feed grass naturally without adding synthetic chemicals to the soil (and eventually, our water table). They may cost a bit more than that sack of synthetics, but the expense seems worth it to me.

After you’ve fed the lawn, give it a light top dressing of commercial compost (home-grown compost may contain weed seeds) or composted manure. If your lawn looks just plain worn out and beat up, it may need more than just fertilizer. Is it brown and patchy, with spots of bare ground? Is there a bumper crop of dandelions? Is the soil hard and compacted? Does water puddle or run off, rather than sink in? Is there thatch, that layer of roots, stems and leaves between the soil and grass blades?

A thin layer of thatch is actually good for the lawn. It provides impact absorption and wear tolerance, and insulates the soil from extreme temperatures. When thatch gets thick, however, weak, unhealthy grass grows in the thatch instead of the soil. If the thatch in your lawn is more than an inch thick, mark your 2005 calendar for an early spring de-thatching job.

There’s a misconception that grass clippings cause thatch buildup. Grass clippings, in moderation, are beneficial. “Grass cycling” adds nutrients and organic matter to the soil and keeps clippings out of the landfill. Thatch is the result of either not enough or too much nitrogen-rich fertilizer, combined with heavy watering. Also, the lower you set your mower blade, the greater the tendency to produce thatch. Recommended mowing heights are between two-and-a-half and three inches.

Using the wrong grass for our area is another major factor in thatch production. Here in Western Washington, turf-type perennial rye grasses and fine fescues are best.

You can begin lawn renovation now by digging out those dandelions and other lawn weeds. Ugh! I know, but you’ve got to do it or you’ll have 10 times as many in the spring.

In April, when you’re just itching to get out in the garden, check that thatch again. If there’s just a little thatch or dead grass, you can use a sharp-tined metal garden rake to get rid of the stuff, allowing air, water and nutrients to reach the soil. If thatch is thick and widespread, consider renting a power de-thatcher (also known as a vertical mower) and core aerator to get the job done.

After thatching, aerate the soil; that is, pierce with a slender, spiked object to allow all the good stuff to get through the grass. You can purchase a hand-held aerating tool that looks like a giant fork, or rent a core aerator for large areas. I’ve seen spiked aerating shoes advertised in garden catalogs, but why not just invite your duffer buddies over to tap dance on the lawn in their golf shoes?

After you’ve de-thatched and aerated, apply an organic fertilizer according to package directions. Then spread new seed and water well.

If you want more detailed information, the Washington State University-Island County Extension office in Coupeville has several useful lawn care publications available for a minimal fee. Call 679-7327 and ask for “Home Lawns” (EB0482) or “Lawn Renovation” (EB0924).

Mariana Graham writes this biweekly column as part of her volunteer duties as an Island County Master Gardener. E-mail her at

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