With the cold weather during the last week (as of Nov. 27, 2013), now is the time for straw mulch to be applied to strawberries. Strawberry mulch is typically spread after plants have been exposed to several nights with temperatures in the lower 20s. Most years this occurs in mid- to late November for strawberry growers in the Lower Peninsula. In mild falls and early winters, like last year, colder temperatures don’t arrive until well into December, even after Christmas some years.
The question of when to apply straw mulch to strawberries is one that growers frequently ask at this time of year. My response is to let your plants tell you when it’s time. After several hard frosts, growers will see the leaves turn red; this is not the time for mulch application. The next step in the hardening process you will see the leaves begin to collapse into the crown or fall over, and finally the leaves will flatten completely to the ground. This last step of leaf flattening is the right timing for mulch application.
Plants mulched too early in the fall do not harden off well or get ready for winter properly. Research has shown that delaying mulch application till just before the ground freezes will result in the highest yields the following season. Most years, however, it is hard to predict when soils will freeze.
Straw mulch primarily serves to protect the plant from cold injury during the coldest parts of winter and reduces the freeze and thaw cycles that are typical in most Michigan winters. The mulch also helps reduce fruit diseases at harvest time by reducing splashing of soil particles that carry diseases onto the berries.
On a practical side, I know growers want to get the mulching finished up before the weather turns cold and nasty, or before fields become too wet.
(Source – http://www.farms.com/news/strawberry-mulching-time-has-arrived-70113.aspx)