Lawns in the Summer

          As the hot weather sets in this summer, there are several stresses that will affect the health of our lawns.  How we manage the lawn during this difficult time will influence how well the lawn comes out of the summer months and resumes healthy growth in the cooler fall months.  Here are some tips for the summertime.

Mowing:  Summertime mowing heights should always be on the high side to reduce wear and tear on the lawn.  The exception would be during cooler than normal and wetter than normal summers (2009).  If you mow your own lawn with a residential tractor or push mower, you should set the mower as high as it goes (probably 3 ½”-4” finished mowing height).  Make sure to sharpen the blade or replace the blade to get the cleanest cut possible to help reduce disease pressure.  If you use a mowing contractor, they should mow no lower than 4”.

          Maintaining longer grass will help shade the ground, protecting the growing points (crown) and roots of the grass plants.  In addition, longer grass will collect more dew each morning and retain moisture much longer than short grass. The interval between cuts should also be longer as well.  Remember that the higher the finished cut (31/2”-41/2”), the longer the grass can go before it needs to be cut again.  During periods of extreme heat (over 90°), DON’T MOW IT, skip a week (or two) between mowings.  If you have a mowing service, ask them not to mow unless it needs it.  Mowing a dormant lawn only damages it and in most cases causes more damage than the hot, dry weather itself.

Watering:  Generally speaking, we do not recommend watering lawns during the summer.  Watering lawns can be time consuming and expensive, which tends to lead to improper watering practices that wastes a valuable resource.  Our lawns (cool-season grasses) will go dormant during hot, dry weather as a natural defense mechanism.  This is a process where the growth rate slows significantly or stops as the plant browns out under the drier conditions.  When rainfall occurs they will resume active growth.  During periods of dormancy, try to reduce traffic on the lawn (mowing, foot traffic) to avoid permanent damage.  Only during periods of extended drought and high temperatures will we recommend supplemental watering.  This would not be enough water to break dormancy, just enough to prevent thinning of the turf due to drought.

          If you choose to water the lawn in the summer, please try to follow these simple rules.  1) Always water in the early morning (preferably finished by sunrise), never in the afternoon or early evening.  Evening water extends the period of time the grass is wet and will fuel the spread of turf disease.  Watering in the afternoon during the heat of the day is the least efficient time to water, losing most of the water to evaporation.  2) Water infrequently for long periods of time, rather than frequently for short periods of time.  Our heavy clay soils do not allow irrigation to soak in quickly.  If you water for short periods of time (15-20 minutes) the water tends to stay at the surface.  If you continue this pattern you will encourage the grass roots to come up to the surface (where the water is), thus weakening your lawn and making it susceptible to other summer stresses (heat, disease, insects). Therefore, soak it!  However long it takes for the ground to become softer under foot (usually 45 minutes to 1 hour to apply ¾”-1” of water).  And then don’t water it again for a week or two if no rain falls.  What you will find is that the surface dries out, but it stays wet several inches down into the soil.  This will encourage your grass roots to stay deep, and you will not be promoting disease. 

          Remember to adjust your schedule based on the amount of rain we receive and the temperatures.  Also take into consideration your sun exposure (full sun vs. shady), slope (flat vs. steep) and the age of your lawn (young and immature vs. mature and well established).  This may vary throughout your property, so adjust accordingly.  Remember, we’d like you to water to ensure the lawn’s survival through the toughest summer conditions, not to make it lush and green.

Turf Disease:  All cool season grasses (K. bluegrass, perennial ryegrass & fescues) are susceptible to attacks from pathogens (diseases) in the soil and/or thatch layer.  All pathogens have ideal weather conditions (temperature and humidity) that must occur in order for them to become active.  Fortunately, the weather typically changes every few days, so even if a pathogen does become active, a change in the weather will cause enough of a variation that the disease will no-longer be active.  Even though we can’t control the weather, we can control our activities on the lawn while stressful conditions or disease activity is occurring.  1) Water smartly.  Prudent watering will help alleviate drought stress, but avoid watering in the early evening or shortly after sunrise.  Lawn diseases need moisture to spread.  Sometimes high humidity or heavy dews create an environment that promotes disease activity, or we may receive a late day thunderstorm, but don’t “fuel” the problem by making the grass wet longer than it already is naturally.  2) Make sure your mower blades are sharp!  Dull blades tear the grass and allow easy entry for disease pathogens.  3) Maintain adequate fertility without over-stimulating the plant.  Most turf diseases occur in lawns growing in infertile soil.  By following a regular fertilization program you can help the lawn to “grow through” periods of disease activity.  But remember that there’s a balance between adequate fertilization and over fertilizing.  Too much fertilizer at the wrong time can create an environment of increased disease pressure.  4) Reduce traffic on the lawn during periods of high temperatures and dry weather.  Weakened grass is more susceptible to disease attacks, so keep the mower and the neighborhood ball game off the lawn during periods of dormancy.

          In most cases when more ideal weather conditions return, turf should recover from disease attacks.  However, there are some situations where pressure from disease is so great that chemical control (fungicide) is warranted.  Keep in mind that fungicides must be used as a curative treatment if activity is evident and that the residual control is short-lived, so generally speaking they are used as a last result.

Weeds:  The best defense against weeds is a thick, healthy lawn.  This makes it difficult for weed seeds to germinate and become established if they blow or wash in from adjacent properties.  However, during the hot, dry summers we normally experience, lawns will go dormant and will be under attack from weeds.  Warm season weeds (oxalis, purslane, spurge, nutsedge, crabgrass) thrive under these conditions and will take advantage of “open” areas of the lawn (bare spots, thin areas & edges).  We employ several different weed controls to keep these weeds under control.  As noted above under mowing, keeping the lawn on the long side will help keep most weeds out of the lawn, but not all weeds.  Also, don’t be too aggressive edging your lawn-especially along driveways and curbs (excessive weed whacking will lead to weed invasion due to soil being exposed along the grassy edge). 

          Due to the summer stresses normally present, spot treatment of these weeds should be the technique used to get them under control.  Be conservative, you can easily cause damage if the lawn is too stressed or if it is too hot.  Don’t apply any weed control if the air temperature is above 85° and use the lowest use rate available to control the target weed.  Keep in mind that the best time to do a blanket application of weed control is in the early fall to “wipe the slate” clean, and then seed two weeks later if needed, to keep your lawn thick.  This will allow you to keep up with your weeds by spot treating them as necessary during the difficult summer season.