Winterizing Strawberries
by Laura McDermott, CCE Eastern NY Commercial Horticulture Program
Providing protection for strawberries during their semi-dormant winter period is increasingly difficult in our warming and unpredictable world, but not any less important. Strawberries need some kind of cover to help prevent desiccation from cold winds and to help reduce freeze/thaw damage to the crowns. Now is the time to consider your options.
Straws from wheat or other grains have been traditionally applied as mulch over the strawberries when soil temperature has consistently dropped below 40oF. This usually happens in late November, although southern locations might not see these temperatures until early or mid-December. Straw is a great winter mulch because it doesn’t mat down, it’s organic and breaks down gradually in the row while it prevents weed growth and provides a relatively mud-free floor for fruit and your U-pick customers.
Level plantings with no raised beds require 2.5 to 3 tons of straw per acre – about 300 small square bales. This will result in a 2-3” layer across the planting. Raised beds could require twice as much mulch because of the tendency for the straw to drift into the alleys off the slippery plastic beds. If you have a small acreage, then applying mulch by hand is the way to go – just shake it out evenly over the plants. If you have a large acreage, you will want to use a bale chopper. Keep an eye on the most windswept areas of your field and replace the mulch if it has blown off.
Straw mulch should be removed in the spring when new green tissue just begins to show. Rake the mulch into the rows. If you want to move your production back, you can do this by delaying mulch removal, but your yield may be compromised. Remember that strawberry plants are only semi-dormant. They tend to start growing regardless of mulch and if photosynthesis isn’t encouraged the fruit number and size will suffer. Plus, there is no guarantee that keeping mulch on longer will help you avoid the frost – the spring of 2023 is a case in point.
After straw mulch is removed many growers use floating row covers as a spring frost protection strategy. These spun-bonded materials allow light and water to pass through but provide several degrees of temperature buffer – depending upon their weight. Heavy-weight row covers (1.25 oz/yd2 or 42 g/m2) can also be useful for winter protection of strawberry plantings. Anchor the row cover with rocks or other weights. Many growers are using a combination of straw and floating row covers, particularly those that are trying to winter a day-neutral strawberry planting. You will want plenty of help and a still day to apply this mulch effectively.
Dr. Elisabeth Hodgdon, CCE ENYCHP, recently led a research trial that examined winter covering strategies. Straw mulch and spun-bonded row covers of several weights with several different application and removal timings were treatments. More details of this work will be shared widely this winter, but one treatment that consistently had better results over two years at two different locations used two layers of row cover instead of straw for the winter mulch. This involved applying a lighter-weight Pro-30 row cover directly on top of the crop in early November and following it up with a second layer of Pro-30 applied in late November. The removal of row covers was also staggered. Applying row cover in November may have increased the temperature of the growing environment so that strawberry plants could set more flower buds in the crown.
Covering strawberries in the winter does improve yield of marketable fruit, but the cost is a consideration. Straw this year may be in short supply. If you have never used row cover, there is a learning curve, and both methods require labor at a time of year when it may be in even shorter supply. Each farmer needs to choose a method that works best with their situation. And lets hope for a good, continued snow cover – that is often the very best winter mulch.