Frost

We received our first hard frost of the year this past Friday evening. This brings the end to the flowers and a beginning to frost delays.

On the golf course frost refers to ice crystals which appear on solid surfaces in the absence of precipitation. There are two such forms of frost: “rime” and “hoar”. “Rime frost” typically occurs under conditions of high atmospheric water content (vapor and/or liquid) and moderate wind speeds. It forms rapidly and adds a dull, matte finish to the surface on which it adheres. Rime formation is most common during cold fogs when water droplets come in contact with subfreezing surfaces. “Hoar frost” on the other hand, forms through the slow deposition of water vapor directly on a surface as ice. This is what we contend with most frequently on turf. It forms best when winds are light, which is often the situation during clear, cold nights. By accumulating slowly, hoar frost forms delicate, interlocking crystals that grow outward from the surface with a feather, fern, or flower pattern. Hoar frost's white color is caused by small air bubbles trapped in the ice crystal that reduces its transparency. The smooth faces of the hoar crystals cause them to glitter in the sunlight, particularly at the low, early-morning sun angles.

Frost occurs on clear cold nights when turfgrass plants reradiate heat. As the plant loses heat to the atmosphere the plant leaf cools. If the plant temperature is cooler than the air temperature then moisture from the atmosphere will condense on the leaf. If the leaf temperature drops below freezing then the water freezes and frost forms. This will occur even if the air temperatures are slightly above freezing. It is not uncommon to have frost form even if the air temperature is in the mid to high 30's. Frost does not form as readily on cloudy nights because the clouds reflect, or absorb and then reradiate the energy back towards the turf. Frost does not form as readily when a breeze is present. The breeze causes convection (a transfer of heat from the mixing of the air closest to the plant with the surrounding atmosphere); this helps to buffer the drop in leaf temperature. This also promotes evaporation of the water droplets from the leaf surface. Areas with little or no slope have a greater potential for frost formation than areas with greater slope. This is because air moves down the slope resulting in a greater potential for mixing. This is manifest when we see heavier frost formation in flat low lying areas.

Frost will normally form early in the morning before sunrise. This makes sense as the plants have been reradiating energy throughout the night, their leaf temperature will be the coolest prior to daybreak. Actually frost may continue to form even after daybreak because the low angles of light coming from the sun may not directly hit the leaf surface. Frost itself does not cause damage to the turf, but injury does occur when traffic is allowed on frosted areas. When frost is present on the grass plant the fluid surrounding the cells becomes frozen and takes on a crystalline formation. The frozen crystals have sharp jagged edges. Cart and foot traffic cause the sharp crystals to rupture the cell walls. This produces internal damage in the leaves of the plant. Turf damage is generally superficial. This is not to say that traffic should be allowed on frosted turf. If traffic occurs, whether it is foot or mechanical, damage caused by crushing the leaf blade will occur. Initially the damage will appear as a purplish to black discoloration of the turf. The damaged turf will then progress to a straw color. This discoloration is visible for a prolonged period of time.

If discolored turf was the only damage that Superintendents had to contend with then play could proceed as normal. Unfortunately there are more profound consequences. The discolored areas are weakened. This turf is more susceptible to disease pressure from fungal pathogens and is vulnerable to weed invasion, specifically Poa annua (annual bluegrass). If damage has not been sustained by the crown of the plant, then recovery will occur from the generation of new leaves. It can take several weeks for this recovery to occur. When the frost burns off, the grass plant thaws and it is possible to let play proceed. Under normal conditions play may proceed when the air temperature at ground level reaches 40 degrees.

Frost delays are frustrating for both golfers and the golf course maintenance staff. Superintendents are sensitive to the needs of their membership. They understand that the delay of an early morning tee time can affect a golfers schedule for the balance of the day. For this reasons we do not delay play unless it is absolutely necessary. Our goal is to provide the best conditions possible for all members and their guests. When frost is present, we monitor the course condition closely. We communicate and work directly with the pro shop so as to open the course as quickly as possible. We appreciate your understanding and patience as we encounter early morning frost delays.