Yard and Garden: Lawn Care

AMES, Iowa – Proper mowing practices play a vital role in helping to maintain a healthy, sustainable home lawn. Lawn mowing is only one question horticulturists with Iowa State University Extension and Outreach answer about lawn care and how to have a lawn with the desired characteristics. Homeowners and gardeners with lawn questions should contact horticulturists at Hortline by emailing hortline@iastate.edu or calling 515-294-3108.

How often should I fertilize my lawn? 

In Iowa, Kentucky bluegrass lawns can be fertilized in spring (April or May), mid-September, and late October/early November. The number of fertilizer applications is largely determined by an individual’s desires or expectations for their lawn.

Three applications of fertilizer (the first in spring, the second in mid-September and a third in late October/early November) would be appropriate for individuals who want a vigorous, dark green lawn. A single application of fertilizer in late October/early November would be sufficient for individuals who prefer minimal fertilization. A moderate fertilization plan consists of an application of fertilizer in mid-September and a second application in late October/early November.

Each application of fertilizer should consist of one pound of actual nitrogen per 1,000 square feet.

When mowing the lawn, what is the proper mowing height?

Kentucky bluegrass lawns should be mowed at a height of 2½ to 3 inches in the spring and fall months. Mow bluegrass lawns at a height of 3 to 3½ inches in June, July and August. A higher mowing height in summer helps to cool the crowns of the turfgrass plants, encourages deeper rooting and provides more leaf area for photosynthesis during the stressful summer months.

Mowing below the recommended range may scalp the turf and cause the turfgrass to deteriorate. Extremely low mowing heights decrease the total leaf surface area, carbohydrate reserves and root growth, creating a situation where the turfgrass plants are unable to produce enough food to meet their needs. This makes the plants more susceptible to drought, high temperature and wear injury. In addition, the bare areas created by a decrease in turfgrass density increase the likelihood of weed problems.

Mowing too high can also create problems. Mowing above the recommended range reduces tillering and causes matting of the grass. Reduced tillering results in fewer and coarser plants, while matted grass creates a micro-environment that encourages disease development.

When should I apply a preemergence herbicide to my lawn to control crabgrass? 

The keys to successful control of crabgrass in lawns are correct timing of the preemergence herbicide application and proper application of the material. Preemergence herbicides must be applied before the crabgrass seeds germinate. If the material is applied too early, crabgrass seeds that germinate late in the season will not be controlled. If applied too late, some crabgrass seeds will have already germinated.

Preemergence herbicides should normally be applied in early to mid-April in southern Iowa, mid-April to May 1 in central Iowa and late April to early May in northern areas of the state. Weather often varies considerable from year to year in Iowa. Accordingly, gardeners should make adjustments in the timing of the preemergence herbicide application. If the weather in March and April is cooler than normal (such as in 2013), apply the preemergence herbicide late in the recommended time period. Apply the herbicide early in the recommended time period if Iowa is experiencing a warm early spring. If you’re still uncertain as to when to apply the preemergence herbicide, Mother Nature provides some helpful (colorful) clues. Preemergence herbicides should be applied when the forsythia blossoms start dropping or when redbud trees begin to bloom. Crabgrass seed germination typically begins after these events.

To insure the herbicide is applied properly, carefully read and follow the label directions on the package. Also, make sure the spreader has been correctly calibrated and is working properly. 

Should I apply lime to my lawn? 

In Iowa, home gardeners should apply lime to lawns only when recommended by a soil test. A soil test will indicate the current soil pH and, if necessary, the amount of lime to apply to the area.

The soil pH is important because it influences the availability of essential nutrients. The pH scale runs from 0 to 14. Any pH below 7.0 is acidic and any pH above 7.0 is alkaline. A pH of 7.0 indicates a neutral soil. The optimum pH range for lawns is between 6.0 and 7.5. Lime is applied to acidic soils with a pH below 6.0 to raise the pH into the optimum range. However, an application of lime to an alkaline soil can raise the soil pH to excessively high levels, reducing the availability of plant nutrients and leading to poor plant growth.

There is no need to apply lime to most lawns in Iowa as few have a soil pH below 6.0. Applying lime to lawns with a soil pH above 7.0 may actually be detrimental.