JoAnne Skelly: Don’t forget to fertilize in late summer

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The hottest days of summer are behind us. As August winds down, it’s the perfect time to fertilize the lawn. We avoid fertilizing the lawn in mid-summer because it over-stimulates the grass leading to faster growth, potential disease and stress, higher water use and more mowing. Over-fertilization can also contribute to thatch buildup.

The most important nutrient for healthy turf is nitrogen, which gives a lawn its nice green color. Most fertilizers contain nitrogen, phosphorus and potassium, the three macronutrients essential to good plant growth. In addition to these, a fertilizer also may contain iron, sulfur or micronutrients. Some fertilizers are inorganic and others are organic. Inorganic fertilizers have a higher analysis than organic fertilizers.

The analysis is the three numbers on a fertilizer package. The first number is nitrogen, the second number is phosphorus and the third number is potassium. A fertilizer that contains all three macronutrients is known as a balanced or complete fertilizer. An analysis of 21-0-0 means the product contains 21 percent nitrogen and no phosphorus or potassium. Many inorganic lawn products have a nitrogen number higher than 21. A 21-0-0 fertilizer works well for most lawns. Most organic fertilizers have a nitrogen value of 10 percent or less. They operate more slowly than an inorganic fertilizer, but they usually contain active soil microorganisms that build soil health, something inorganic fertilizers don’t do.

Soil type can influence which fertilizer you use. Inorganic slow release or organic fertilizers are best on a sandy soil to prevent leaching of fertilizer into surface or ground water. Clay soils and soils high in organic matter can hold an inorganic fertilizer in place and reduce leaching.

You should need less fertilizer each year if you leave your grass clippings on the lawn. Grass clippings recycle some of the nutrients you have applied. Grass clippings do not increase thatch accumulation in lawns.

By fertilizing now and again in late September or early October while the grass still is green and at least two to three weeks before the ground begins to freeze, you may be able to avoid an April fertilizer application next year. Many horticulturists believe the most important fertilizer application is the one in October.

Some people choose fertilizer — weed killer combinations for their lawn. These products are primarily herbicide with very little fertilizer. I don’t recommend these combo products for that reason and for the fact that they can damage trees, shrubs and other plants.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at or 887-2252.


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