Protecting strawberries from spring freeze and frost

In the spring after removing straw, frost and freezing temperatures can injure strawberry buds and blossoms and reduce yield.

Frosts and freezes are not the same, but both can injure strawberry plants. Freezes are when the temperature drops below 32°F. Frost can occur above or below 32°F and happens when the dew point is below freezing and dew freezes on the plants.

The blossoms are more sensitive to freezing than the leaves, and they become more cold-sensitive as they open and bloom.

Before the flower buds have fully opened (tight bud stage) the buds can survive at temperatures as low as 20° F. Once the blossoms are open, they are damaged at 30° F.

Monitor the forecast and temperature in the strawberry field as cold weather is approaching, to assess whether it is necessary to protect the field against frost or freeze. Have tools in place to prevent injury, in case this occurs when flowers are starting to form.

Two common methods for cold protection in strawberries include:

• Overhead irrigation
• Floating fabric row covers

You should acquire one or both tools as soon as you start growing strawberries, so you are always prepared in case of freeze or frost.

Overhead irrigation

Strawberry Farming - Overhead Sprinklers for Irrigation and Frost Protection (video: 03:51)

Using overhead irrigation during cold temperatures can protect strawberries from frost and freeze damage, as long as temperatures do not fall below 20° F. It is very important to have an overhead irrigation system set up, as cold temperatures during bloom are common.

Irrigation for frost protection is only effective when used correctly. Growers should read thoroughly about this practice before using it. Not applying enough water or stopping irrigation too early during a nighttime freeze, can cause more damage than not irrigating at all.

This method works when the water from overhead irrigation freezes and mixes with the sugars in the leaves and flowers. As the water changes to ice, it releases heat. So this only works if water is continuously applied during the freezing period and until temperatures rise above freezing. If irrigation is stopped too early or only applied for a short time during a freeze, it can cause more harm than good.

If the air temperature drops below 34°F after flower buds have emerged, start the overhead irrigation system.

• Apply approximately 0.1-0.2 inch of water per acre per hour (3600 to 5700 gallons per hour) with one sprinkler head revolution per minute.
• Alter the application rate depending on the wind speed, temperature, and humidity. Higher wind speeds and lower air temperatures require higher volumes of water to work.

Spring frost protection is unnecessary during the planting year in day-neutral strawberries because the flowers are usually removed until the danger of frost is past. And they are often planted after the risk of a hard frost has passed. Frost protection in the fall can extend the harvest season.

For more information:

• Irrigation For Frost Protection Of Strawberries
• Principles of Freeze Protection for Fruit Crops
• Midwest Plan Service handbook on Sprinkler Irrigation Systems

Row covers

In addition to irrigation, fabric and plastic row covers may also be used to protect strawberry plants from frost and freeze events in the spring.

Frost damage can still occur in places where the row cover is directly touching the blossoms.

The type and weight of the row cover fabric affect how well it protects the plants against frost. A row cover weighing 0.6 ounces per square yard can increase the temperature underneath by 2-3 degrees. Double-layer plastic can increase the inside temperature by up to 10 degrees.

Apply row covers the afternoon before freezing temperatures are expected in order to trap in heat.