Reasons for Lawn Problems
Although there are many specific reasons to which one could attribute lawn problems, the most common general reasons include:
- Poor management decisions; soil compaction, improper mowing, irrigation, fertilization, and pest management.
- Using poorly adapted species or cultivars.
- Limitations in resources; water, time, labor, and cost.
Mowing
The two most important aspects of mowing are height and frequency. For all lawn species, the recommended mowing height is between 2.5 and 3 inches. Mowing lower than 2 inches can reduce drought and heat tolerance by promoting shallow roots and limiting photosynthesis, while also increasing the risk of weed invasion. On the other hand, mowing too high may encourage insects, diseases, and weeds. It’s best to maintain a consistent mowing height throughout the year. There’s no need to mow turf shorter in late summer or fall.
Turf should be mowed often enough so that no more than one-third of the grass height is removed at a time. For bluegrass or fescue lawns, this may require mowing every three to four days during the active spring growth period, but only once every seven to ten days during periods of slower growth caused by heat, drought, or cold. If mowing is delayed due to weather or other factors, temporarily raise the mower height to avoid removing too much at once. Then, a few days later, mow again at the normal height.
Allow grass clippings to fall back onto the lawn while mowing, unless you plan to use them as mulch elsewhere in the landscape. Clippings decompose quickly, returning valuable nutrients—equivalent to one to one-and-a-half fertilizations per year—and organic matter to the soil. While a mulching or recycling mower makes this process easier, any mower can effectively recycle clippings as long as the one-third mowing rule is followed. Grass clippings do not contribute to thatch buildup.
Lawn Clippings and Surface Water Pollution
Lawn clippings and leaves mowed, swept, or blown onto the street are the major source of phosphorus pollution in urban lakes and streams. When using side-discharge mowers, mow in a direction that keeps clippings off streets, driveways, and other hard surfaces. Never sweep or blow clippings into gutters or the street, as they can easily wash into storm drains and harm local waterways. [Figure 1] Also, leave an unmowed grass buffer strip edging any lakes, streams, ponds, and wetlands. [Figure 2]
In a natural setting, rain and snowmelt absorb mostly into the soil. Air-borne pollutants and pollen washed out of the air are broken down by soil microorganism activity. The nitrogen and phosphorus released from the decay of grass, leaves, and other organic matter recycle back into the soil.
However, in the landscape setting, the water cycle is greatly changed by large areas covered by hard surfaces such as streets, driveways, walks, parking lots, compacted soils, and buildings.
In a typical landscape setting 55% of rainfall moves as surface runoff, compared to only 10% in a naturalized setting. Nutrients from grass and leaves along with fertilizers, pesticides, and other water-soluble pollutants readily wash off the hard surfaces into the storm sewer system. Here the pollutants end up in local streams, ponds, and lakes.
Fertilization
Selecting a Lawn Fertilizer
Nitrogen (N) is the most important nutrient for maintaining healthy turf color and growth. However, applying too much nitrogen—especially in spring and summer—can overstimulate the grass, leading to thatch buildup in some species, as well as increased mowing and watering needs. On the other hand, too little nitrogen can result in poor color and thinning turf, particularly in species like bluegrass and ryegrass. Thin turf is more vulnerable to weeds and disease. It’s important to understand that different turf species have varying nitrogen needs and optimal fertilization times throughout the year.
Balanced or complete fertilizers contain varying amounts of phosphorus, potassium, iron, and sulfur. While these products are a good safeguard against potential nutrient deficiencies and generally safe to use, they may not always be necessary. When grass clippings are left on the lawn, many of these nutrients are naturally recycled back into the soil, reducing the likelihood of deficiencies. Aside from nitrogen, the most commonly deficient nutrient in lawns is iron (Fe).
Organic fertilizers can be just as effective as synthetic options, but it’s important to understand how each type releases nutrients. Organic fertilizers typically release nutrients more efficiently when soils are warm and moist. In contrast, many synthetic fertilizers are effective even when soils are cooler—though some synthetic products are designed to mimic the slow-release behavior of organic sources. Knowing these differences helps ensure fertilizers are applied at the right time for best results.
Better lawn fertilizers include a quick release form of nitrogen for quick green-up, plus slow-release forms of nitrogen for sustained greening. Examples are listed in Table 1.
Table 1. Example of Quick and Slow-Release Fertilizers
| Quick-Release Nitrogen for fast green-up | Slow-Release Nitrogen for sustained green |
|---|---|
| Ammonium sulfate Ammonium nitrate Potassium nitrate Urea | Resin-coated urea Sulfur-coated urea Isobutylidene diurea (IBDU) Methylene urea Urea formaldehyde Compost and manure Poultry waste Poultry feathers |
When to Fertilize and How Much To Apply
The natural grass growth cycle influences proper fertilization time for lawns. Spring fertilizer applications promote vigorous growth of shoots and leaves resulting in increased turf density and overall darker green color of the lawn. Heavy spring fertilizations reduce carbohydrate energy reserves and stress tolerance.
Fall fertilization on cool season turf enhances storage of carbohydrate energy reserves, strengthens root system, increases shoot density, increases stress tolerance, develops better fall and winter color, and results in earlier green-up the following spring.
Timing and Application Rate
Timing and application rates are given in Table 2. If lawn clippings are returned to the lawn, reduce application rate by ¼ to one-third.
Table 2. Fertilizer Application Schedule for Established Colorado Lawns1, 2 Nitrogen application rates are in pounds of nitrogen per 1,000 square feet of lawn area.
| Turfgrass Species | Mid-March to April3 | May to mid-June | July to early August | Mid-August to mid-September | Early October to early November4 |
|---|---|---|---|---|---|
| High Maintenance Bluegrass and Ryegrass5 | ½ – 1 | 1 | Not required | 1 | 1-(2) |
| Low Maintenance Bluegrass5 | ½ | ½ – 1 | Not required | 1 | (1) |
| Turf-Type Tall Fescue5 | ½ | ½ – 1 | Not required | 1 | (1) |
| Turf-Type Fine Fescue5 | ½ | ½ – 1 | Not required | ½ – 1 | Not required |
| Buffalograss6 Blue Grama6 Bermudagrass6 | Apply no N | ½ – 1 | ½ – 1 | Apply no N | Apply no N |
Fertilizers and Water Pollution
Home lawn management has a significant impact on the protection, or pollution of surface water. While lawns are often unfairly blamed for contributing to water pollution, it is not the lawn itself but the way it is managed that poses a risk.
Fertilizers and pesticides (including herbicides, insecticides, and fungicides) that are spread onto hard surfaces such as driveways, sidewalks, streets, or compacted soils can easily be washed into nearby lakes, streams, and ponds through stormwater runoff. This runoff is not treated before entering natural water bodies.
Phosphate fertilizers, when applied to lawns or garden soils, typically bind to soil particles and do not leach into groundwater. However, phosphorus can still reach surface water through soil erosion.
Organic fertilizers are not inherently safer for the environment. The potential for pollution depends on how and where any fertilizer is applied. Overapplication or careless spreading, especially onto impervious surfaces, increases the risk of nutrient pollution. In most Western soils, phosphate fertilizers are not needed for lawns. Responsible fertilizer use, guided by soil tests and proper application techniques, is essential for protecting water quality.
Irrigation
Lawn water needs vary widely, as many factors influence how much water is required. For example, a healthy, high-quality bluegrass or ryegrass lawn may need as much as 2 to 2¼ inches of water per week during hot, dry, and windy summer conditions. However, water requirements decrease significantly during cooler or cloudy weather. Table 3 gives the typical water requirement (rain plus irrigation) per week for lawns. Turf-type tall fescue may perform well with less irrigation than a bluegrass lawn if it can grow a deep root system and the soil in which it is growing is holding usable water. In many cases, however, a tall fescue may require as much water as bluegrass to look good. Actual water use for any turf type varies day to day depending upon factors such as temperature, wind, humidity, and solar radiation (sunny or cloudy).
Table 3. Typical Water Requirement (Rain Plus Irrigation) for Colorado Lawns
| Late April | May & June | July & August | September | Early October | |
|---|---|---|---|---|---|
| Inches of water per week (Irrigation plus rain) | 0.75 | 1.0 | 1.5 | 1.0 | 0.75 |
Buffalograss and blue grama lawns can remain green for weeks without irrigation, even during the hottest summer weather, with rainfall providing the only source of water.
Shady lawns and areas sheltered from wind generally require less water over the growing season than turf in more exposed locations, provided the turf is not competing with the roots of large trees. In mature landscapes, where trees and shrubs share the same soil, water demand may actually increase due to competition among plant roots. A healthy lawn maintained through proper mowing, fertilizing, and cultivation will use water more efficiently.
How Much Water?
Each time you water your lawn, try to apply enough water to moisten the entire root zone. Use a soil probe or shovel to check rooting depth. If roots extend six inches deep, water until the soil is moistened to that depth. It’s important to know both how deep your turf roots grow and how far the water is actually penetrating. Watering too deeply, especially in sandy soils, can waste water as it moves beyond the root zone where plants can’t use it.
How Often Should a Lawn Be Watered?
Lawns growing on sandy soils need to be watered more frequently than those on clay or loam soils. Sandy soils retain little plant-available moisture, even after thorough watering, so they require lighter, more frequent irrigation. In contrast, turf on clay soils can be watered less often but with larger amounts of water. Less frequent watering improves efficiency by reducing evaporation and may help limit weed growth.
Conversely, turf growing on clayey soils can be irrigated less frequently, with larger quantities of water. Watering less often means more efficient water use because of less loss to evaporation. It can also reduce the number of weeds that appear in the lawn. With most soils, do not apply all the water in a short period of time. If applied too quickly, water will run off thatchy turf, from sloped areas, or from turf growing on heavy clay or compacted soils. In these cases, it is more effective to apply only a portion of the water and move the sprinkler or switch to another station to water another section of the lawn. Cycling through irrigation stations (“soak cycles”) will promote infiltration and reduce runoff and puddling in low spots. This allows water to soak into the soil rather than run off.
Core cultivation (aeration) can help improve water infiltration by relieving compaction and reducing thatch. Wetting agents may improve water movement in the soil but are not a substitute for addressing underlying issues like compaction or excessive thatch.
What are Some Signs that Turf Needs to be Watered?
A clear sign that turf needs water is a wilted appearance. One early indicator is “footprinting,” where footprints remain visible on the lawn for an hour or more after walking on it. This is typically followed by actual wilting, where the grass takes on a grayish or bluish-purple hue. If only a few dry spots consistently appear in the same areas, spot-watering those sections can help delay irrigating the entire lawn by a day or two. These “indicator spots” serve as an early warning that the rest of the lawn will soon need water.
A hardened or toughened lawn, attained through less frequent, deep irrigation, often withstands minor drought, and generally has fewer disease problems. It is important, however, that the turf is not allowed to become overly drought-stressed between waterings. This weakens the turf and makes it more susceptible to insect and disease damage and to weed invasion.
During extended dry periods from late fall to spring, it may be necessary to “winter water” every four to six weeks if the ground is thawed and will accept water. Pay particular attention to exposed slopes, sites with shallow soil, and south or west-facing exposures, where winter mites may infest and kill drought-stressed turf during the winter and early spring.
The most efficient time of day to water is late evening or early morning (between 9 p.m. and 9 a.m.). It generally is less windy, cooler, and more humid at this time, resulting in less evaporation and more efficient use of water. Water pressure is generally better, optimizing sprinkler distribution patterns. Contrary to widespread belief, watering at night (after 9 p.m.) does not encourage disease development in turf.
Thatch
Thatch is a tight, brown, spongy, organic layer of both living and dead grass roots and stems that accumulates above the soil surface. Factors that lead to thatch problems include the following:
- Sod over compacted soil. When sod is laid over compacted soils, a thatch problem will develop in a couple of years.
- Soil compaction is a common contributor to thatch build-up as it slows the activity of soil microorganisms.
- Over fertilization is a common contributor to thatch build-up as the lawn may be growing faster than microorganisms can break it down.
- Grass species. Thatch tends to be a problem on Kentucky bluegrass, bentgrass, and fine fescue lawns. It is rarely a problem with tall fescue or buffalograss.
- Frequent heavy irrigation may contribute to thatch as lower soil oxygen levels slow the activity of soil microorganisms.
- Pesticides. Excessive use of some pesticides may also slow soil organism activity.
Grass clippings do not contribute to thatch accumulation and should be returned to the lawn during mowing to recycle the nutrients they contain.
Measure thatch depth by removing a small piece of turf, including the underlying soil. Up to ½ or ¾ inch of thatch is acceptable and will enhance traffic tolerance. The thatch depth can increase quickly beyond this point, making it difficult to control later. As the thatch layer thickens, it becomes the main rooting medium for the grass. This predisposes the turf to drought stress or winterkill and increases the possibility for insect, disease, and weed problems. In addition, fertilizers and pesticides applied to a thatchy lawn work less effectively.
Power Raking for Thatch Management
This method of thatch removal has been used for years. Light (shallow) power raking may be beneficial if done often. Deep power raking of a thatch lawn can be damaging, and often removes a substantial portion of the living turf. Used properly, power raking of wet, matted turf can speed spring green up by letting air move into the root zone and warm the turf. Compost all removed thatch and organic material to kill any living grass before it is used as a mulch or soil amendment.
Core Cultivation or Aerating
This can be more beneficial than power raking. It helps improve root zone conditions by relieving soil compaction, while controlling thatch accumulation. Soil compaction, in fact, is one factor that contributes to thatch buildup. Aeration removes plugs of thatch and soil two to three inches long (the longer, the better) and deposits them on the lawn. Enough passes should be made to achieve a two-inch space between holes.
What is done with the cores is a matter of personal choice. From a cultural perspective, there may be an advantage to allowing the cores to disintegrate and filter back down into the lawn. Mingling soil and thatch may hasten the natural decomposition of the thatch. The little fluffs of thatch and turf that remain behind can be collected and composted. Depending on soil type, core disintegration may take a few days to several weeks. Irrigation helps wash the soil from the cores. Running over dried cores with a rotary mower can be effective but will dull the blade. If the cores are removed from the lawn, compost before using as a mulch or soil amendment.
Soil Compaction
Soil compaction is the most common problem in lawn quality. With reduced soil oxygen levels, rooting systems will be shallower. With compaction, the grass roots have reduced access to water and nutrients. Irrigation and fertilization will need to be lighter and more frequent.
Aerating (removing plugs) once or twice a year will help reduce soil compaction in an established lawn area if enough passes are made to yield plugholes at two-inch intervals. The best time of year to aerate a lawn is late August to late September, as fewer weed seeds germinate this time of year. Aerating the lawn area around a tree is also the best method to promote tree vigor. [Figure 3]
Weed Management
Lawn weed killers provide only temporary control if management factors that favor weeds are not addressed. In a thin turf with heavy traffic, weed problems may intensify following the use of weed killers. When the weeds (which help absorb the wear and tear of foot traffic) are removed with weed killers, the lawn may thin. The thin lawn opens the soil to increased weed problems.
Soil compaction is the primary cause of weed problems. Weed management factors include the following.
Core aeration – Soil compaction favors weeds and discourages lawn growth. Common lawn weeds that thrive in compacted turf include annual bluegrass, black medic, chickweed, clover, crabgrass, knotweed, prostrate spurge, and plantain. Clover may be a good companion crop for lawns in compacted soils, filling in between the thin grass.
Mowing – High mowing height (shading) and frequent cutting discourages weeds.
Watering – Deep, infrequent watering will “drought out” many common shallow-rooted lawn weeds.
Limited fertilizer – A thick, actively growing turf chokes out most weeds. However, fertilizer will not thicken up a turf when soil compaction is the growth-limiting factor.
Insect and Disease Management
In semi-arid climates like Colorado, turf insect and disease problems are minimal compared to other areas of the nation. Frequent use of lawn insecticides may increase the occurrence of lawn insect problems. Some garden insecticides have a potential to kill birds feeding in the treated areas (refer to the insecticide label). Thus, avoid unwarranted treatments of lawn areas.
When controlling soil insects, the insecticide must be watered into the root zone to be effective. Some insecticides get held up in the thatch and do not water in effectively.
In semi-arid climates like Colorado, lawn diseases are minimal, compared to other areas of the nation. With Colorado’s dry climate, fungicides do little to nothing for home lawn disease management. Cultural practices (fertilizer, watering, and soil compaction) are the keys to disease management. [Table 4]
Table 4. Influence of Cultural Practices on Kentucky Bluegrass Diseases
| Soil Compaction | High N | Low N | Thatch | Irrigation | Mowing | |
|---|---|---|---|---|---|---|
| Ascochyta Leaf Blight | Yes | Yes | Yes | Timing | Yes | |
| Necrotic Ring Spot | Yes | Yes | Yes | Drought with heat | Yes | |
| Leafspot and Melting Out | Yes | Yes | Yes | Yes | Timing (wet/dry cycle) | Yes |
| Gray Snow Mold | Yes | Yes | ||||
| Dollarspot | Yes | Yes | Yes | Drought | Low | |
| Striped Smut | Yes | Yes | ||||
| Fairy Ring | Yes | Yes | Yes |
This publication, reference GardenNotes #551, is developed as part of the Colorado State University Extension Master Gardener Program.