would a high speed fan keep frost away from top of tall palm

[nicebutdim]

Must find their names again cuz I've lost the website's bookmark after changing my laptop.
What kind of plants are you gonna protect this way?

a large washingtonia robusta ,it's about 3.5m or more and impractical to cover

[countrylover]

Well I have found NU FILM 96 and VaporGard. I've no idea about hteir availability in the UK. Alsoto know their prices I'd neet to contact the supplier.

[simon]

I doubt that air movement will stop frost formation. Surely if the leaf surface is below the due point, frost will form regardless. In fact blowing more moist air over the leaves would surely cause the frost to build up a thicker layer. As has been said already, unless you blow warmer air in from elsewhere, I don't think it will work and on the coldest mid winter nights, you won't find any warmer air. The orchard example is just during late spring at times when marginal frosts could damage delicate blossom. You are talking about mid winter and severe frosts here.

[nicebutdim]

Moist air would not be directed onto the leaves as the fan would be directed upwards ,surely this would deflect the air away,coupled with the drying effect of wind.I have noticed in the past that irrespective of ambient temperature the leaves are unharmed if protected from above, allowing air to circulate as long as the covering in this case,it was fleece did not actually touch the leaves allowing moisture to permeate.Some time ago it was reported farmers were spraying crops(not possible in my case ) and the spraying effect while causing much moisture did not allow frost to develop.Cold air falls so the fan would prevent it falling hopefully.

[simon]

Cold air falls, yes, but during a frost the cold is generated at ground level due to ground radiation. The cold ground then draws heat from the air immediately above it. This cold air pools at ground level unless there is a breeze to mix it with the warmer air above. On still nights fans could be used to replace the missing breeze and disperse the pooling cold air but this would only protect low growing plants, not tall palms. Obviously it depends on the depth of the temperature inversion.

Protecting plants only from above works because leaf surfaces loose heat through radiating in the same way as the ground does, so providing a barrier allows that radiation to be reflected back to the leaves thus preventing them from loosing heat. You are then less likely to get frost formation because the leaves should remain the same temperature as the air. Air movement will not prevent heat loss through radiation.

Spraying reduces the risk of freezing because of the latent heat in the water but I think this is again only used during marginal frosts in spring to protect new growth and wouldn't be useful in the depths of winter.

[Dave Brown]

Must find their names again cuz I've lost the website's bookmark after changing my laptop.
What kind of plants are you gonna protect this way?

a large washingtonia robusta ,it's about 3.5m or more and impractical to cover

Mine is about 3m and you won't stand a chance with just a fan. I went about it the other way by stopping warm air rising, then the rope lights were about 100w

SEE HERE for the full topic on 2009/10 Washingtonia winter protection

[nicebutdim]

Unfortunately mine have a neighbouring screen of leylandi type trees preventing the erction of a brolly, the wind also would I imagine take it away.That seems to be a perfect solution in your setting