As we start to see bloom in strawberry fields frost protection may be necessary in some areas this week. Keep an eye on the forecast and keep in mind that fields are often colder at ground level than the forecast. Depending on the temperature growers can use row covers, irrigation, or a combination of the two to protect their fields.
Critical temperatures for strawberries at different stages of development are listed below (Perry & Poling, 1985):
Stage of Development
Approximate Critical Temperature (°C)
Irrigation will offer more frost protection than row covers alone. If you need to irrigate make sure you have enough water to irrigate for a couple nights in a row if necessary. Make sure the ice freezing on the plants is clear. If the ice is cloudy or milky white the application rate is not fast enough to protect the bloom. More information on strawberry frost protection can be found in this article: Irrigation for Frost Protection of Strawberries (full URL: http://www.omafra.gov.on.ca/english/crops/facts/frosprot_straw.htm ), including detailed information on when to start irrigating and how much water to apply. Irrigation can be stopped once the ice begins to melt in the morning.
If you don’t have sprinklers for frost protection, irrigating (with drip tape or travelling gun) before the frost event will help if the soil is dry. Irrigate before the soil cools; the plants should be dry at night.
Row covers reduce evaporative cooling and the rate of cooling under the cover. Row covers offer 1-3oC of protection, depending on the weight of the cover and manufacturer, which could provide enough protection depending on the stage of your crop and the temperature. Row covers can also be used to buy time on a frosty night. Two 1- ounce row covers will offer more protection than one 2-ounce cover.
Row cover + irrigation
If using a combination of row covers and irrigation you will need to measure the temperature under the row cover. Begin irrigating right over the cover once the temperature reaches 0.6oC under the row cover, and stop when plant temperature starts to climb.
Parts of the province are expecting snow this week. Snow will provide some insulation to strawberries. Row covers can be used as well to provide additional protection.