50 degrees before disturbing flower beds

Asked April 16, 2019, 7:56 AM EDT

I have read recently that cleaning up leaves and debris in gardens before the temp has reached 50 degrees can harm hibernating bees. Can you clarify if that refers to 50 degrees over a certain sustained period or just the first time the thermometer hits the mark. Using a rake sounds like more of andisturbance than a leaf blower, but they would probably be equally as disturbing right?

Charlevoix County Michigan bee health

2 Responses

Unfortunately there is no one-size-fits-all solution for our overwintering pollinators. "Pollinators" are an incredibly diverse group and each species has its own preferences for overwintering habitat and emergence timing (temperature).
With regard to bees, (which are still a very diverse group), we can make some generalizations. First of all, most of them overwinter underground or inside of cavities, so they will not be in the leaf litter during the winter. The tricky part is that once the temperatures start to rise above 50 degrees Fahrenheit, some of our early season bee species might start to emerge from their overwintering shelters. Once they emerge, they will not return to the shelters, so on cold nights they might seek shelter in the leaf litter in your flower beds. Raking the leaves gently, or removing the litter by hand will not cause them too much harm. And, then, if you place the litter in a safe location, they will be able to fly once the temperature warms up and they should be no worse for the wear. Removing those same leaves in the spring with mechanical equipment like a leaf blower is likely to cause them harm unless it is used on a very low setting. A leaf vacuum or mulching mower would almost certainly kill any bees that got sucked into it.
Of course, removing the leaves before the temperature rises above 50 degrees (i.e. before they leave their overwintering shelters) could also be an option. Or you could do your yard cleanup on a nice warm sunny day in the late morning or early afternoon when you are pretty sure any sleeping bees are out looking for food. It is probably worth mentioning that the "50 degree rule" is more of a rule-of-thumb because species vary greatly in their temperature thresholds for activity.

This is helpful. Thank you.