Do Roots Grow in Winter?

[dbonsaiw]

There are times I wish there was a way to have a camera under the soil to see what's going on down there. Do roots on dormant trees grow during the winter? I find that there are a ton of roots growing out the grow boxes when I take them out of the mulch pile in spring. I just have no idea when those roots actually grew.

 

[AlainK]

Do roots on dormant trees grow during the winter?

More or less...

If they are in a mulch pile, the heat from the decomposing much can possibly keep the bottom roots in activity, so yes, they can grow a bit in winter as long as they do't get frozen.

 

[Michael P]

Yes, depending on soil temperature. Below 36F there is very little growth and all growth stops at 32F.

 

[AlainK]

"32F" in the civilized world -- is 0°C, when water starts to freeze.
Definitely no root activity at that temperature. Roots don't grow in a frozen soil, for some species they are even damaged if that stays for several days.

I think the bottom temperature must be a bit higher for roots to be reactivated, at least 4-5°C (39-41F), 24 hrs for several days, and nights.

Other soil living organisms (micro-fauna or mycorrhyzae) are also dormant below zero, so the roots are inactive too because the symbiosis is at sleep.

 

[Dav4]

I seem to remember someone like @Leo in N E Illinois mentioning that root growth stalls when soil temps fall below 40 F. With that being said, some of my own maples, usually in nursery cans and mulched on the cement floor of an unattached garage in zone 6a MA in late November when outside temps were approaching 20 F, would have root extensions 6+ inches long coming out of the drain holes when pulled from the mulch as it thawed the following March. Mind you, the surface of the mulch was always frozen solid by New Years, but was clearly warmer lower down for some time.

 

[Bonsai Forest]

There are times I wish there was a way to have a camera under the soil to see what's going on down there. Do roots on dormant trees grow during the winter? I find that there are a ton of roots growing out the grow boxes when I take them out of the mulch pile in spring. I just have no idea when those roots actually grew.

@ the 35-minute timestamp, the discussion of winter care moves into the subject of warming beds. Very interesting how keeping the root system warm can perpetuate root growth without compromising dormancy and/or overall health of the tree.