Horticulture Turfgrass Specialist
Iowa State University Extension & Outreach
As the leaves change and colors of fall become more beautiful, it is also the ideal season to complete turfgrass maintenance practices. It is the most important time to focus on cultural practices of mowing, aeration, fertilization, and seeding. The work you do now helps your lawn recover from summer stresses and prepares it for another long Iowa winter. This article will provide the necessary steps to ensure a healthy lawn through the fall months and next spring.
Mowing is the most time consuming maintenance practice, but many aspects of mowing are misunderstood and performed incorrectly. Proper mowing practices play a vital role in helping to maintain a healthy, sustainable home lawn. Because lawns often look attractive after mowing it is easy to assume that grass thrives on mowing. In reality, mowing is a very destructive process that injures the grass plant. Each mowing temporarily stops root growth, decreases carbohy¬drates, increases water loss, decreases water absorp¬tion by the roots, and creates entry points and susceptibility to diseases. Therefore, it is important to minimize these stresses with sound and consistent mowing practices.
In general, taller mowing heights result in healthier grass that is better able to resist drought as well as possible harm from weeds, insects, and diseases. The “correct” height depends on the grass species and environmental conditions.
Kentucky bluegrass and the fine leaf fescues can be mowed slightly shorter compared to perennial ryegrass and tall fescue. Mowing below these recommended heights can result in a rapid decline in lawn quality.
Mowing height should be increased temporarily during stressful high-temperature periods. Raising the mowing height results in a deeper root system and helps the plant find necessary water and nutrients. The additional leaf tissue also allows the grass plant to produce more energy, that helps plants better withstand stressful periods. However, mowing well above the recommended heights can lead to a thin, spindly lawn where the grass plants lay over on themselves (matting). This condition can result in increased disease development.
|Recommended Mowing Heights|
|Species||Cool Weather||High Temperature Stress Periods|
|Mowing Height (inches)|
|Kentucky Bluegrass||2.00 - 2.50||2.50 - 3.00|
|Perennial Ryegrass||2.00 - 2.50||2.50 - 3.00|
|Fine Leaf Fescues||1.50 - 2.00||2.00 - 2.50|
|Tall Fescue||2.00 - 2.50||2.50 - 3.00|
|* In lawns where species are mixed, use the higher of the two recommendations.|
How often should I mow?
The decision whether to mow should be based on the growth of the grass, not by a set weekly schedule. The grass species, time of year, and rainfall are all influencing factors of rate of growth. You will notice that during the spring, your lawn will grow at a much faster rate and require more frequent mowing. As fall approaches, the tissue growth slows and more plant resources are focused towards the root system.
As a general rule, mow as often as needed so that no more than one-third of the total leaf area is removed in a single mowing. For example, a lawn maintained at 3 inches should be mowed before it reaches 4.5 inches. Removing more than one-third of the total leaf area can result in scalping and is detrimental to plant health. Shorter lawns require more frequent mowing.
Perennial broadleaf weeds can be controlled with an application of a broadleaf herbicide in the fall (late September to early November in Iowa). In the fall, perennial broadleaf weeds are transporting carbohydrates from their foliage to their roots in preparation for winter. Broadleaf herbicides applied in fall will be absorbed by the broadleaf weed’s foliage and transported to the roots along with the carbohydrates, resulting in the destruction of broadleaf weeds. The most effective broadleaf herbicide products contain a mixture of 2 or 3 herbicides as no single compound will control all broadleaf weeds. The most common broadleaf herbicides are 2,4-D, dicamba, triclopyr, MCPP (mecoprop), and quinclorac.
It is important to remember that some broadleaf herbicides may affect new seedlings. To avoid damage, wait to apply herbicide until new seedlings have been mowed two or three times.
Thatch and Aerification
Thatch is an intermingled layer of living and dead plant material that accumulates above the soil surface. It bears a resemblance to a spongy peat moss layer. Thatch can be beneficial and problematic. Thatch supplies necessary food sources for microbes and organic matter. However, excessive thatch can harbor diseases and insects. Thatch that is properly balanced promotes growth and appearance of a well-groomed lawn. Proper balance of thatch requires a combination of management practices. These include preventing thatch buildup by reducing plant growth by only adding necessary nitrogen fertilization and the mechanical removal of thatch when necessary. It is important to remember that tall fescue, fine fescue and perennial ryegrass are other lawn spe¬cies used in Iowa that seldom develop thatch problems.
A core aerator punches hollow tines into the soil and removes small soil cores about the size of your index finger. Core aerating should not be looked upon as a method of removing large amounts of thatch. Rather, it is most effective as a means of preventing thatch from developing and reducing soil compaction. Homeowners who have lawns receiving high maintenance should have annual core aerating.
A vertical mower is the most common machine to physically remove excess thatch that has accumulated over time. The vertical mower has evenly spaced knife-like blades that rotate perpendicularly to the thatch surface. The vertical mower blades slice through the thatch and about 1⁄4 inch into the soil surface. It is important to set the machine low enough so that some soil is depos¬ited on the surface. After vertical mowing, hand rake the loose thatch from the surface and leave the soil. In addition to dethatching, a vertical mower can be used when renovating and preparing the surface for overseeding. A power rake is another type of machine used to remove thatch. It is different from a vertical mower because it has spring steel tines that loosen thatch without cutting into the soil. Vertical mowing and power raking are effective means of removing thatch; however, the slicing and ripping action during dethatching causes consider¬able stress on the lawn. For cool season grasses, such as Kentucky bluegrass, early fall dethatching is most desirable.
Aeration, vertical mowing, and power raking services are available from some professional lawn care companies and the machines are usually available at rental companies.
The best time to seed a lawn in Iowa is between mid-August and mid/late September. However, lawns can be successfully established as late as late-September in central Iowa and early October in southern Iowa. Late summer planting is preferred to spring seeding because seeds germinate and grow rapidly in the warm soil. The warm days and cool nights are ideal for seedling growth.
Fertilization is very important at the time of seeding. This is the only time you will be able to incorporate required soil amendments or fertilizer into the root zone. Prior to preparing the seedbed, broadcast fertilizer according to soil test recommendations, then incorporate to a depth of 4 to 6 inches. Soil testing information can be found at here.
Select high quality seed of the grass species best adapted to the site. Perennial ryegrasses may be included in seed mixtures for spring plantings to help the lawn establish quickly. However, for late summer planting, a mixture of three or four Kentucky bluegrass varieties is preferred in areas that receive full sun. Fine fescue is the most shade-tolerant grass recommended for Iowa lawns. Fine fescue that will not grow in your shade situation should be replaced with shrubs, ground covers, or mulches that are suitable for low light conditions.
Divide the total seed quantity in half. Using a dropseeder, sow one half in one direction and the other half at right angles to the first. After the starter fertilizer and seed have been broadcast, lightly rake the area to cover the seed to a depth of no greater than 0.25 to 0.5 inches. Seeding depth varies based upon seed size. The larger the seed size, the deeper it can be covered with soil. Roll the area lightly to firm the soil around the seed.
Grass seedlings are very susceptible to desiccation and the surface of a newly seeded lawn should not be allowed to dry. Water should be applied only in amounts necessary to keep the soil surface moist. Avoid overwatering and runoff. Two light applications of water per day will usually be sufficient unless it is hot and windy. In more extreme conditions, up to four light waterings per day may be necessary.
When irrigation is not available, mulching the lawn with clean (weed free) straw will help conserve moisture and prevent erosion. One to 1.5 bales of straw per 1,000 square feet will give a light mulch covering that will not have to be removed after germination. There are also other mulching materials available for lawn establishment. These include pelletized new paper and excelsior (wood shavings) mats.
The number of applications depends on the desires/expectations of the homeowner, soil type, cultural practices, and other factors. A single application of fertilizer in late October/early November containing 1 pound of nitrogen per 1,000 square feet may be sufficient for low maintenance lawns. Highly maintained lawns may need additional fertilizer in the spring (0.5 – 0.75lb./N per 1,000), September (0.75 – 1 lb. /N per 1,000), and a late October/early November (0.75 – 1 lb. /N per 1,000).
For additional information on any of these topics, refer to the following publications: