Arilyn Tegtmeier-Oatman, Rachel Perry, and Ajay Nair
Department of Horticulture
Iowa State University
Frost and freeze damage affect countless fruit and vegetable growers leading to yield losses and occasionally the loss of the entire crop. Learning how to manage and mitigate losses due to frost is crucial in continuing to grow vegetables, especially in the Midwest, and to maximize both yields and profits for both large and small scale farms. Frost damage occurs when the temperature briefly dips below freezing (32°F). With a frost, the water within plant tissue may or may not actually freeze, depending on other conditions. A frost becomes a freeze event when ice forms within and between the cell walls of plant tissue. When this occurs, water expands and can burst cell walls. Symptoms of frost damage on vegetables include brown or blackening of plant tissues, dropping of leaves and flowers, translucent limp leaves, and cracking of the fruit. Symptoms are usually vegetable specific and vary depending on the hardiness of the crop and lowest temperature reached. The table below shows some of the light-frost susceptible and tolerant crops that are grown in Iowa.
|Light-frost Susceptible||Light-frost Tolerant|
|Sweet potato||Onion (plants)|
There are multiple ways growers can manage frost and reduce the damage caused. Commercial growers often rely on passive or heated high tunnels, greenhouses, hoop houses or cold frames to prevent frost damage to vegetable crops. To manage spring frost events, growers rely on low-cost methods such as the use of floating row covers. These covers are supported above the crop using wire or metal hoops, or bent PVC hoops (Fig. 1). Row cover edges are commonly weighted with sand bags, long plastic pins, or simply buried with soil to prevent loss due to wind. Row covers come in varying sizes and weights, providing different levels of frost protection. A heavier grade material (1.5-2.0 ounces per square yard; Fig. 2) will provide higher degree of frost protection than the lower grade (0.55 ounces per square yard; Fig. 3). Hoop house and greenhouse structures can be more effective when used in conjunction with interior floating row covers. This double layer of protection creates a microclimate at plant level that can be significantly warmer than exterior temperatures. As covers grow heavier, the light transmission drops, meaning less photosynthetic activity will occur unless covers are removed. Additionally, row covers are not self-venting, meaning growers must remove the cover on sunny days to prevent overheating.
All of these techniques are viable options to be implemented within vegetable production systems. Depending on the crop, materials available, and budget growers can determine which of these techniques is best suited for managing frost in their respective farms.
|Figure 1. Row covers in the field.|
|Figure 2. Heavier row cover material.|
|Figure 3. Lighter row cover material.|