Fans or no fans?

[Mike Corazzi]

Getting set for winter with its small freezes in central California, I'm debating an issue.
My trees are actually under a patio overhang. The sun gets to all of them really easily and for all practical purposes, they are outside. Even though "technically" under a cover. Rain hits them easily.
So.... my issue is whether ceiling fans are a good or bad thing to use during any freezes.
Would the air circulation (it's not vigorous) tend to DRY the trees? Or would the air circulation keep them FROM freezing.

So, good or bad on fans above trees?

The soil HAS frozen from mid 20's F. before.

???

 

[barrosinc]

What trees are we talking about? I live in 9b and I leave the trees outdoors all year. I protect blooming flower trees and ficuses from frost but nothing else...
We get to mid 20s too a couple of nights a year. But this low temp is achieved at 6 to 7AM so only lasts a very small amount of time.
Have you had any problems in the past?

 

[amatbrewer]

I could be totally wrong and am interested in what others have to say, but in an outdoor situation I would think a fan would do little more than dry out the trees, unless there is a way you could get cold pockets where your trees are, in which case the fans could prevent that (in my area farmers use large wind machines for this).

In an confined space like my greenhouse/cold box where it is tall but narrow, I can get large differences in temperature between the top and bottom, so a fan helps.

 

[Shinjuku]

Would the air circulation (it's not vigorous) tend to DRY the trees?
Yes. The only question is will be enough to matter?

Or would the air circulation keep them FROM freezing.
Probably not. If the ambient air temperature is 32 degrees, simply circulating air at that temperature would not increase the ambient air temperature. But if you had a nearby spot where the ambient air is warmer, the air circulation could distribute that heat around the trees. At the same time, the air right against your house may be warmer than the air out in your yard, and the fan could blow that warm air away and make it colder for the trees. But since warm air rises, air near the ceiling of your patio may be warmer than sir bear the floor, and the fan could push that warm air down to the trees. So many variables.

I’d suggest that you do an experiment. Get a thermometer and a way to measure moisture in your pots and try it both ways, measure, and see what works. And let us know so we can all learn.

 

[Leo in N E Illinois]

My initial thought would be yes, the fans are a good idea, and would help prevent adiabatic cooling type frosts, and not make maters worse when it just plain gets so cold you are gonna freeze. If warmth is coming off the building, and pooling under the overhang before dispersing, the ceiling fans could mix the warmer air down and delay freezing that way too.

Adiabatic frosts are where the air temp is actually above freezing all night, but as the sun comes up in morning, super cold high elevation air aloft, suddenly falls due to heat from the sun causing the atmosphere to begin mixing. This super cold air will fall, and frost areas especially in open exposed areas, and for trees on the ground rather than on benches or stands. This is why the weather channel can say you were above freezing all night, and yet you have frost or freeze burn on trees in open spaces. The NWS has their thermometers 2 meters (6 feet) off the ground in a louvered box on a post. The cold air drops past the box to the ground, the thermometer in the box does not ''see'' this cold falling air.

Trees are evolved to handle breezes. Yes, the moving air could dry the trees out a little quicker, but this should not be a significant concern. Outdoor air is the normal ambient humidity, it won't dry the trees out excessively fast. Do keep an eye on watering when you make the change and leave the fans on, it will alter the watering frequency but won't hurt the trees.

 

[Mike Corazzi]

 

[Velodog2]

Oh The Weather Chanel says that? Well then.

 

[Leo in N E Illinois]

I probably did not explain it very well. I may have confused some details. Don't think I could do better, if adiabatic frosts are still a confusion head to Wikipedia or National Weather Service website, they will explain it far better than I ever could.