The Theory of Relativity

By Bob Vavrek, senior agronomist, North Central Region
June 16, 2011

Raising the height of cut on greens to 0.175” - 0.200” will facilitate faster recovery from winter injury.  Covering a green during early spring to raise soil temperatures and taking the putting surface out of play will also help promote rapid healing. 


It’s been an interesting spring across the upper Midwest; waiting, waiting and waiting for a sustained period of warm weather to arrive.  There have been short teasers, such as two consecutive days of temperatures above 100 degrees last week, but sweater weather returned within 48 hours of the oppressive heat.  The numerous courses affected by significant winterkill have suffered the most.  Recovery has progressed at a snail’s pace and many greens are still affected by localized areas of thin and bare spots just waiting for Poa annua to ultimately fill into the voids.

Attempts to encourage rapid recovery on greens have varied widely between courses.  Some course have done little more than spike in a little bentgrass and apply starter fertilizer, while others in Minnesota have constructed propane heated tents over damaged turf to increase soil temperature enough to germinate bentgrass in April.  No doubt, some techniques have performed better than others. 

One tidbit of sound recovery advice that I sometimes overlook is the need to raise the height of cut of the greens throughout the recovery process and not raise just a little, but a lot.   The relationship between faster recovery and generous mowing heights was clearly evident on a recent tour of a course that experienced winter injury to relatively new bentgrass greens.

However, “raising” the mowing height is a concept relative to the typical mowing height of greens when they are healthy, and that base value tends to shrink by a few thousandths every season.   Long gone are the days when kicking up the height a notch meant raising the bench setting from 5/32” (0.156) to 3/16” (0.187).    Mention a mowing height of 3/16” to a recent turf school graduate and they look at you as though the bedknives must have been made from chipped flint by a Neanderthal. 

The lesson I learned this spring is that raising the height of cut to facilitate recovery means just that…raise the height of cut.  Changing from 0.105 to 0.120 doesn’t mean squat to an immature bentgrass seedling because it won’t tolerate either height at that stage of growth.  Who would build a new bentgrass green and then mow for the first time at 0.120?  Yet, some courses believe the big dead spot of Poa will somehow transform into bentgrass by seeding into a 40 degree root zone of nearly straight sand and then raising the mowing height all the way up to 0.125.  

There are a slew of factors to consider if you want to achieve rapid recovery from winter injury and that discussion is more appropriate for a Turf Advisory Service visit versus a short regional update.  Forget about small relative changes in mowing heights as they are hardly worth the trouble. The take home message this month is to really raise the mowing height (0.175 - 0.200) if you really want to recover sooner than later. 

Source:  Bob Vavrek, or 262-797-8743 


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