Snow and Cold Weather Complicate Fall Mulching for Strawberries

Photo: Three inches of snow covers the ground west of the Twin Cities, October 20, 2020. Annie Klodd 

Between cold temperatures and snowfall this week, it can be confusing to decide when to lay down mulch for strawberries.

Straw is typically applied some time in November, depending your location and the weather. A very general rule is to apply mulch once temperatures dip below 20 degrees F, as long as the plants have had a chance to go dormant and acclimate to late fall temperatures. Another precise, research-based rule is to wait until the soil temperature has remained at or below 40 degrees F at 4 inches depth for at least 3 consecutive days.

Bottom line: It is important to wait until the plants go dormant to apply mulch, so that they do not keep growing underneath the straw. 

However, the cold temperatures and snow this week make following these rules a little more interesting.

Since the plants were still growing as of a few days ago, they are unlikely to be dormant, and the soil temperatures are probably not low enough yet.

Forecasts say that temperatures will remain between the low 30s to mid 20s until the weekend, when some areas, such as Alexandria, will dip to temperatures low enough to injure the strawberry crowns (low teens). Additionally, many areas of Minnesota, including Duluth, the Twin Cities, and Alexandria, received between 2-4 inches of snow today (Tuesday, Oct. 20).

According to Steve Poppe, UMN researcher and former strawberry grower in western Minnesota, growers can and should still hold off on mulch application for a couple more weeks, despite the cold weather, to make sure the plants go dormant first. 

While extreme temperatures could injure the crowns, the risk of mulching them before dormancy could do more harm than good, and snow will help insulate the crowns anyway.

While temperatures could remain so cold the rest of this week that the plants go dormant, growers are not advised to rush to apply mulch in areas with snow cover. The snow does two things: 1) It makes applying mulch logistically challenging, and 2) It provides some insulation from extreme low temperatures. 

Determining if the Plants Have Gone Dormant

To determine if the plants have gone dormant and it is time to spread mulch, Poppe and other strawberry experts recommend the "plywood test." 

Once you think the plants may have reached dormancy, place a piece of plywood over a few of your strawberry plants. Wait a couple of days. If the leaves of the plants under the straw have turned yellow, then the plants were not yet dormant. If they remain green, they were dormant at the time the plywood was applied and it is ok to put down straw.

How much straw to apply

Once you have determined that it is time to apply mulch, 2.5 to 3.0 tons of straw per acre should be applied, covering the plants by 2 to 3 inches. 

For more information

Mulching Strawberries for Winter Protection - Rich Marini, Penn State University

Mulching Strawberries - Richard Jauron, Iowa State University

Author: Annie Klodd, University of Minnesota Extension Educator - Fruit and Vegetable Production