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It's about time for Frost

September 25, 2009

This week historically brings the first opportunity for frost in a good portion of the state. Fortunately, that doesn’t necessarily mean the terminal end to the growing season for our cool season grasses, unlike many other plants and crops here in Iowa. Frost formation can come in
many levels of severity affected by environmental factors such as low temperature, dew point, relative humidity, wind speed, cloud cover, and elevation. Turf managers only slightly control a few factors such as irrigation and moisture availability, applications of wetting agents, and cutting heights of the turf. Frost formation on turfgrass will begin or advance the entrance into dormancy as the plants prepare for the winter months. Though, the main concern that is always on the mind of the turf manager is damage to the plants due to traffic on frost laden turf. This can be a concern on all turfgrass areas, but especially on grass such as on golf course greens.

Pictures of traffic damage on frosted turf by Zac Reicher, Purdue University

Light frosts that are essentially frozen dew on the upper leaves of the turfgrass plants as the temperature approaches 32 degrees. This typically occurs close the coldest point of the night usually around sunrise, or in golf course terms right when you would like to mow. As the ice forms on the plant it begins to freeze the plant cells in the tissue of the turgrass leaf. This weakens the cells and makes them vulnerable to permanent damage, kind of like cracking an egg. In general, most damage primarily occurs on the leaf tissue, but in heavier frost events and on lower mowed turfgrass the damage can extend down into the crown. If the frost traffic occurs and cells near the growing point are damaged, the plant could be a complete loss.
This issue of the frost setting in causes not only delays in your maintenance system, but delays in golf play or other turf activities. The key is that time is money. So, we all want to limit the time our employees are at the shop, or golfers are holding up tee times, etc.
What can we do to limit these time delays? One practice that is commonly used is a light irrigation cycle which contains water that is warmer than 32 degrees to melt off the frost and warm up the surface. The issue with this is that it must be timed properly to not form more ice on the system. The other thing to remember is that the irrigation will only knock the frost off of areas it can reach, so cart or foot traffic damage can occur leading to the irrigated areas.
I have included a chart referenced from a past issue of Horticulture Home and Pest News authored by Richard Jauron. As you will see the data is somewhat dated, but after conversations with State Climatologist Harrry Hilaker the fall dates still are very accurate. The spring dates and growing degree days may change slightly.


As with all issues involving the weather it is hard to tell what might actually happen. Good luck finishing up the growing season!

Neric Smith,
Commercial Horticulture Program Specialist
Iowa State University Extension


March Weather Summary and Frost Watch

April 9, 2012
Although we have been spoiled by unseasonably warm temperatures frost could be an issue for a little while longer.

Keep the winter jacket handy at least for a little while longer. After experiencing summer-like weather conditions during the month of March, most of the state is under a freeze watch for Monday and Tuesday night. These more “normal” temperatures will feel anything but considering the very abnormal spring temperatures to date.

Temperatures in central Iowa averaged 55.7 F during March which is 16.4 degrees above normal. Overall, there were 12 days during March when the daytime temperature was in the 70’s or 80’s. The warmest day of the month occurred on the 16th with a high of 84 F. Now, we must prepare for frost. Historical weather records show that the average last date for frost occurs sometime between mid-April to the first week of May depending on your location in the state.

So what exactly is frost? Frost is the formation of white ice crystals on an exposed outside surface such as leaf blades. Annual plants are often more sensitive to frost and will need to be brought in or covered to be protected from the freezing temperatures. Luckily, our perennial turfgrasses are more tolerant and frost in and of itself will not cause damage to plant tissue. However, damage from frost can occur if there is traffic on the turf while frost is present.

Cart or even foot traffic is enough to cause damage. Because the cells within the plant are primarily water when the temperatures gets below freezing this water can also freeze. Traffic on frozen turf causes the ice crystals to puncture cell walls within the plan. Even though the turf will appear alright the damage has occurred internally. Frost damage symptoms include white to light tan leaves where traffic has passed. In time, the turf will acquire a brown to blackened color. Damage is usually limited to leaf tissue and will remain until new growth replaces the damaged turf. Mowing will help remove some of the damaged tissue and improve the overall appearance of the turf. In severe cases, damage can affect the crown of plant.

Frost damage on a creeping bentgrass fairway.  Here, damage was the result of cart traffic on turf when frost was present.

It’s difficult to prevent frost from occurring and perhaps the best strategy is communicating with the golf course staff. Have them to pay special attention to low-lying areas and shady areas. Cold air tends to settle into these areas and will likely be the last place frost melts. Just because there isn’t frost on the putting green which is exposed to full sun in the morning doesn’t mean the entire facility is clear.

Irrigation can be used to help speed up the melting process through the release of latent heat. When water changes from a liquid to a solid by freezing it gives up heat. In actual practice, surface temperatures will be held around freezing as long as liquid water is available. A light syringing of the turf can aid in this process.

Covers can also be used to protect turf from freezing temperatures although placing and removing covers is a labor intensive process. Newly seeded turf or renovated areas where recovery needs to occur will benefit from the heat trapped under the cover.

Until you reach your frost free date, keeping people off the course when frost is present is the best way to prevent damage.

Marcus Jones
Assistant Scientist