WINTERKILL (also referred to as winter damage or winter injury) usually occurs in bermudagrass, St. Augustine, and sometimes very slightly in zoysia. It shows up as areas that simply do not green up in the spring. The damage is caused by three different weather conditions, either separately or in combination.
- Extremely cold temperatures, below 5 or 10 F for more than one 24-hour period.
- Very dry, high speed winds, usually from the north or northwest, combined with temperatures of less than 20 degrees for several days or intermittently for several weeks.
- Snow piling up (whether by shoveling or wind) that does not melt for a long time, with intermittent thaw and freeze cycles. This may occur along the north sides of houses or fences where the snow and ice may accumulate and stay for several weeks.
Winter damage may occur anywhere the grass is thin or the soil is compacted, under the drip lines of trees, along privacy fences, and the north side of any structure. It can also occur along the edge of any concrete surface. Cold temperatures radiate down through the concrete sidewalk, curb or driveway and freeze the ground and the grass’s root system, killing it. The damage may extend from just a few inches to a foot and a half out.
You can help prepare your lawn to better withstand damaging winter conditions by doing a few things in the fall. For the last several mowings, leave your lawn longer so that the roots have more insulation. Refrain from weed-eating or edging around concrete so that you have extra insulation there also. When we have a dry spell in the fall or early winter, especially if winds are high for any length of time, water your lawn when it’s warm enough to get out and do so. Dry grass and roots are much more likely to sustain damage than irrigated turf. But sometimes, no matter what you do, winter conditions may be harsh enough to sustain winter injury anyway.
FREEZE DAMAGE is closely related to winter damage. It normally occurs only in the spring, and only in bermuda. As spring approaches, the thin areas of the bermuda begin to green up first because the sun will warm up the soil temperature more quickly due to less thatch covering. If we get a freeze after these areas have begun to green up, damage will occur. If temperatures drop into the mid to low 20's, you could see severe damage. (This is one of the reasons we advise NOT to scalp your lawn until all danger of freezing has passed.)
Coincidentally, and unfortunately for us, winter damage, freeze damage, and Spring Dead Spot all become noticeable after we have applied our first application, making many think we damaged the lawn somehow. (We didn't.)
FROST DAMAGE Frost damage occurs in the fall on bermuda or zoysia. It has no lasting ill effects on the grass, but it looks strange, and many people call us when they see it. When we have a frost or two when bermuda is still green, you will see a zigzag striated pattern of green and brown on the lawn. This just means that the lawn is starting to go dormant, and no actual damage to the grass has occurred.
The following links will take you to some good articles regarding winter injury to turfgrass and landscapes.
Article in the Tulsa World detailing the extent of winterkill from our 2009-2010 winter
Oklahoma State University commenting on the 2009/2010 winterkill.