Sometimes softer in summer?

It may seem counterintuitive that golf course conditions may not be as firm during periods of hot, dry summer weather, as they are during cooler periods when we receive more consistent rainfall.  However, there are several reasons why this may occur, most of which involve the irrigation system, and the frequency and scheduling of irrigation cycles:

• Let's start with the irrigation system itself.  Our system was designed in the 1980s and doesn't provide the uniformity of coverage of a more modern design.  Despite having employees spend up to 500 man hours per month hand watering to supplement coverage deficiencies, we still can't provide the uniformity of rainfall.  Thus, at times, it feels like Goldilocks--this area is too wet, this area is too dry, this area is just right.
• Given the hit or miss nature of rain events in the summer, there are occasionally times when we schedule an irrigation cycle, not willing to take the risk that we "might" get a shower or thunderstorm.  For example, last Friday was forecast to be a washout with temperatures staying in the 70s...then they called for showers...followed by a change to rain from the city south.  And how did the day actually turnout?  Brilliant sunshine and low humidity with a high of 85.  A day that was expected to add moisture to the soil profile, instead ended up lowering moisture levels.  We are fortunate to have an on-site weather station and the ability to remotely initiate or suspend irrigation cycles, but it's easy to feel like you need a crystal ball to accurately know the upcoming weather and schedule the irrigation accordingly.

Friday's weather surprised many.

• With cool season turf, the longest root system of the year is in the spring.  With less stressful environmental conditions, and plenty of roots to bring moisture and nutrients into the plant, going long periods between rain or irrigation isn't a problem at that time of year.  However, as you can see below, in August, cool season grass has the shortest roots of the entire year.  In the case of Poa greens the "functional root sytem" this time of year may be less than one inch in length.  Allowing the soil to dry beyond a point where the roots can access moisture, can quickly spell trouble.

The shortest roots of the year are in August.

• The greens are designed to drain well, and the Dryject treatment they received in the spring has increased the water infiltration rate.  The data for the graph below comes from one of the sensors buried in #1 green.  The spike in moisture seen in the orange line was caused by a fairly significant rain event of .70".  However, within 24 hours after the rain, moisture levels at a 2" and 7" depth in the green are very close to the pre-rain numbers.  In this situation, the rain didn't provide a reservoir of moisture which the turf can draw from for several days, and irrigation may be required.   

• Finally, as we enter August and get ready for aerification, we need to be sure we have good, uniform soil moisture.  Similar to surgery on a person, aerifying has long-term health benefits for the turf, but it also causes some temporary stress.  We need to have a healthy "patient" in order to minimize the risk of post-surgical complications (like wilt), and help speed recovery.

Soon enough, fall will be here, a season which often leads to some of the best playing conditions of the year.