Where's the Snow? Is There Potential for Winter Injury in Strawberries?

With the rather mild and snow-free winter we have been experiencing in south and south-central Manitoba questions of winter injury potential to strawberry plants has become a topic of discussion. We need to remember that strawberry plants are considered a tender perennial on the prairies and require additional winter protection to survive our extreme winter temperatures. This is typically done with straw mulch, which protects the crop from low temperature injury to crowns and shallow root systems. When properly applied, straw mulch keeps soil temperatures more uniform, prevents plants from drying out from cold and dry winds, prevents frost heaving of crowns and helps trap snow.

Plants with and without straw, with minimal snow

Winter injury to strawberry plant crowns can occur when subjected to extended periods of cold temperature, where the crown tissue core temperature drops to -12°C to -20°C. This injury will appear in the spring as a browning of crown tissue, which is typically creamy white when healthy. This injury will usually lead to crown mortality or severely stunted plants the next spring. When crown core temperatures drop to -6°C to -9°C for extended periods of time, this can cause a decrease in leaf numbers, stunted leaves, fewer flowers and fruit as a result.

However the presence of a uniform, 2-3 inch layer of straw mulch will usually be sufficient to maintain crown temperatures above those temperatures (-6°C to -9°C), even without snow cover. Many regions of US and Canada use the straw mulch winter protection system and typically do not have reliable uniform snow cover but experience winter temperatures similar to Manitoba. Strawberry plantings in Alberta, Saskatchewan, North Dakota, South Dakota, etc. typically do not experience extensive winter injury damage using straw mulch without snow cover.

Typical strawberry plant depth in soil

Fortunately we have not been subjected to extreme winter temperatures (-20°C to -30°C) for extended periods of time in Manitoba where snow cover has been absent. Bare soil temperatures recorded at the various southern Manitoba stations of the Manitoba Ag Weather Program have been in the range of -4°C to -9°C during December 2011 and January 2012. We would expect crown core temperatures under straw mulch to remain in the –3°C to –4°C range, well below the winter injury temperature range.

Research has also shown that daughter plants are typically more winter hardy than mother plants, this could be due to the lower placement in the soil of the crown of daughter plants than the mother or different rates of cold acclimation or physiological development. In most winters all strawberry plants will experience slight degrees of winter injury, seen in the form of slight browning of crown tissue, but this will typically not have a significant impact on overall yield.

Overall, strawberry fields with adequate layers of straw mulch will keep strawberry crown core temperatures more uniform, prevents the plant from drying out from cold and dry winds, prevents frost heaving of crowns and will help trap any snow that is available. The uniform strawberry plant temperatures may be the most important of these benefits given the extreme fluctuations we have been experiencing on a weekly basis - above freezing for several days to well below freezing for several days. We still need to be concerned with the potential occurrence of winter temperatures in the -25°C to -30°C range for extended periods as the winter winds down in Manitoba in regions without snow cover.  Continue to monitor your strawberry fields and ensure that straw mulch is not being removed by wind or displaced by deer attempting to feed on dormant plants. 

References

The Importance of Straw Mulch on Strawberries (PDF 636KB), Anthony Mintenko, Fruit Crop Specialist, MAFRI

Straw Mulch for Winter Protection in Strawberries, Midwest Strawberry Production Guide. Department of Extention. The Ohio State University.

Cold Acclimation in Strawberries: How Strawberry Plants Get Ready for Winter, Pam Fisher - Berry Crop Specialist, OMAFRA

Boyce, B.R. and Reed, R.A. 1983. Effects of bed height and mulch on strawberry crown temperatures and winter injury. Adv. Strawberry Prod.2: 12-14.

Turner, J.M., Tanino, K. K. and Stushnoff, C. 1983. Evaluation of low temperature hardiness of strawberry plants under field and controlled conditions. Can. J. Plant Sci. 73:1123-1125.

Yao, S., Luby, J.J. and Wildung, D.K. 2009. Strawberry Cultivar Injury After Two Contrasting Minnesota Winters. HortTechnology Vol. 19 no. 4:803-808