How much does wind chill effect plants? I assume that because it's a
calculated figure intended to give humans some idea of how cold it
feels, then an air temperature of say 2C with a wind chill of say -3C
doesn't actually mean plants will freeze (assuming they would anyway
at sub-zero temperatures). But I also assume that, because of the
effect of the wind, plants will actually reach that 2C much quicker
than they would do in still air, and that their own individual
microclimate within the 'envelope' of the plant would be greatly
reduced or literally blown away.

Which brings me on to fleece. In still air (or almost so) I assume
fleece works by preventing loss of heat by radiation and thus prevents
a ground frost settling on the plant. In windy conditions, I assume
that the fleece goes some way to preserving the microclimate within
the envelope of the plant (see above) and so provides some insulation
and also prevents desiccation to some degree. Is there a rule-of-thumb
as to how much frost protection can be achieved with fleece and under
what conditions? I assume it depends to some degree on wind strength.

Am I right? Any views or experiences?


--
Chris

E-mail: christopher[dot]hogg[at]virgin[dot]net

In article ,
Chris Hogg wrote:
How much does wind chill effect plants? I assume that because it's a
calculated figure intended to give humans some idea of how cold it
feels, then an air temperature of say 2C with a wind chill of say -3C
doesn't actually mean plants will freeze (assuming they would anyway
at sub-zero temperatures). But I also assume that, because of the
effect of the wind, plants will actually reach that 2C much quicker
than they would do in still air, and that their own individual
microclimate within the 'envelope' of the plant would be greatly
reduced or literally blown away.

I believe that a lot of plants are not actually harmed by the freezing
as much as the desiccation. The freezing stops the water transport,
and the ice sublimes in dry conditions, especially with a wind. This
would explain why a single night's frost is less damaging than a
long period of the same temperature.


Regards,
Nick Maclaren.

The message
from Chris Hogg contains these words:

How much does wind chill effect plants? I assume that because it's a
calculated figure intended to give humans some idea of how cold it
feels, then an air temperature of say 2C with a wind chill of say -3C
doesn't actually mean plants will freeze (assuming they would anyway
at sub-zero temperatures).

Correct. With the caveat however that evaporation can be accelerated by
a dry wind passing over plant tissue or wet leaves, and this can reduce
the temperature of the plant's surface by a small amount.

But I also assume that, because of the
effect of the wind, plants will actually reach that 2C much quicker
than they would do in still air, and that their own individual
microclimate within the 'envelope' of the plant would be greatly
reduced or literally blown away.

Yes.

Which brings me on to fleece. In still air (or almost so) I assume
fleece works by preventing loss of heat by radiation

No, by convection, and thus conduction to the cool air surrounding the plants.

and thus prevents
a ground frost settling on the plant. In windy conditions, I assume
that the fleece goes some way to preserving the microclimate within
the envelope of the plant (see above) and so provides some insulation
and also prevents desiccation to some degree. Is there a rule-of-thumb
as to how much frost protection can be achieved with fleece and under
what conditions? I assume it depends to some degree on wind strength.

In windy conditions at lower altitudes there is seldom frost, though we
might be in for a drop shortly if the weather forecast is correct.

Am I right? Any views or experiences?

I've never used fleece, but if you manage to secure it and stop it
flapping about I'd guess that it would offer some protection while
frosty wind made moan.

--
Rusty
horrid dot squeak snailything zetnet point co full-stop uk
http://www.users.zetnet.co.uk/hi-fi/

In article , Nick Maclaren
writes
In article ,
Chris Hogg wrote:
How much does wind chill effect plants? I assume that because it's a
calculated figure intended to give humans some idea of how cold it
feels, then an air temperature of say 2C with a wind chill of say -3C
doesn't actually mean plants will freeze (assuming they would anyway
at sub-zero temperatures). But I also assume that, because of the
effect of the wind, plants will actually reach that 2C much quicker
than they would do in still air, and that their own individual
microclimate within the 'envelope' of the plant would be greatly
reduced or literally blown away.

I believe that a lot of plants are not actually harmed by the freezing
as much as the desiccation. The freezing stops the water transport,
and the ice sublimes in dry conditions, especially with a wind. This
would explain why a single night's frost is less damaging than a
long period of the same temperature.

Similar for wind itself, even without low temperatures - the wind aids
evaporation, increases transpiration, water uptake from soil can't keep
up with the loss through the leaves, therefore the plants suffers the
effects of drought.

With low temperatures there are two mechanisms at work, one the effect
of the temperature (turning nasturiums to pulp, for example), the other
the 'drought' effect - for example potted primulas which are OK until
the pot itself is frozen through and they can no longer obtain water.
But pelargoniums succumb quickly to frost, whereas they are perfectly
capable of coping with drought, so with them it must be the temperature
itself. Ditto cacti.
--
Kay
"Do not insult the crocodile until you have crossed the river"

In article ,
Kay wrote:

With low temperatures there are two mechanisms at work, one the effect
of the temperature (turning nasturiums to pulp, for example), the other
the 'drought' effect - for example potted primulas which are OK until
the pot itself is frozen through and they can no longer obtain water.
But pelargoniums succumb quickly to frost, whereas they are perfectly
capable of coping with drought, so with them it must be the temperature
itself. Ditto cacti.

Yup. There is also the slightly bizarre effect of reversible damage,
as with Cyclamen coum, where the leaves go dull and flop, but recover
when they thaw out. I don't know what the mechanism is there.


Regards,
Nick Maclaren.

In article , Nick Maclaren
writes
In article ,
Kay wrote:

With low temperatures there are two mechanisms at work, one the effect
of the temperature (turning nasturiums to pulp, for example), the other
the 'drought' effect - for example potted primulas which are OK until
the pot itself is frozen through and they can no longer obtain water.
But pelargoniums succumb quickly to frost, whereas they are perfectly
capable of coping with drought, so with them it must be the temperature
itself. Ditto cacti.

Yup. There is also the slightly bizarre effect of reversible damage,
as with Cyclamen coum, where the leaves go dull and flop, but recover
when they thaw out. I don't know what the mechanism is there.

Could be in any way related to the flopping and recovery through lack
of water?

I once froze a Ficus benjamina. It lost all its leaves and appeared
dead, but recovered a few months later - after which all its leaves had
a matte rather than glossy finish. It was still going strong several
years later, still with matte leaves.
--
Kay
"Do not insult the crocodile until you have crossed the river"

In article ,
Kay wrote:

Yup. There is also the slightly bizarre effect of reversible damage,
as with Cyclamen coum, where the leaves go dull and flop, but recover
when they thaw out. I don't know what the mechanism is there.

Could be in any way related to the flopping and recovery through lack
of water?

Unlikely. It is completely unlike the plants' response to drought,
and is fully reversible. The leaves recover their normal texture
and appearance.

I once froze a Ficus benjamina. It lost all its leaves and appeared
dead, but recovered a few months later - after which all its leaves had
a matte rather than glossy finish. It was still going strong several
years later, still with matte leaves.

A different effect, though perhaps related.


Regards,
Nick Maclaren.

In article , Nick Maclaren
writes
In article ,
Kay wrote:

Yup. There is also the slightly bizarre effect of reversible damage,
as with Cyclamen coum, where the leaves go dull and flop, but recover
when they thaw out. I don't know what the mechanism is there.

Could be in any way related to the flopping and recovery through lack
of water?

Unlikely. It is completely unlike the plants' response to drought,
and is fully reversible. The leaves recover their normal texture
and appearance.

It sounds very similar from the description you have given. In what way
is the response to frost and drought different?


--
Kay
"Do not insult the crocodile until you have crossed the river"

In article ,
Kay wrote:

It sounds very similar from the description you have given. In what way
is the response to frost and drought different?

With frost, the leaves go limp and change colour overnight and
recover the following day. With drought, they do neither, but
sort of shrivel - and it is not reversible.

I have seen that mainly in Cyclamen coum, but some other plants
have a hint of the same behaviour.


Regards,
Nick Maclaren.

In article ,
Jaques d'Alltrades wrote:

and thus prevents
a ground frost settling on the plant. In windy conditions, I assume
that the fleece goes some way to preserving the microclimate within
the envelope of the plant (see above) and so provides some insulation
and also prevents desiccation to some degree. Is there a rule-of-thumb
as to how much frost protection can be achieved with fleece and under
what conditions? I assume it depends to some degree on wind strength.

In windy conditions at lower altitudes there is seldom frost, though we
might be in for a drop shortly if the weather forecast is correct.

But, when the two occur together, it is very damaging.


Regards,
Nick Maclaren.

The message
from (Nick Maclaren) contains these words:

In windy conditions at lower altitudes there is seldom frost, though we
might be in for a drop shortly if the weather forecast is correct.

But, when the two occur together, it is very damaging.

Implied...

--
Rusty
horrid dot squeak snailything zetnet point co full-stop uk
http://www.users.zetnet.co.uk/hi-fi/

In article , Nick Maclaren
writes
In article ,
Kay wrote:

It sounds very similar from the description you have given. In what way
is the response to frost and drought different?

With frost, the leaves go limp and change colour overnight and
recover the following day. With drought, they do neither, but
sort of shrivel - and it is not reversible.

Ah, right. Not coum, but other cyclamen I have seen the leaves go limp
(without shrivelling) and recover after a good soaking, in other words,
very much you decription of the frost effect. Other plants, of course,
do the flopping and recovering thing with great panache - ever seen a
peace lily trying to tell you it needs water?


--
Kay
"Do not insult the crocodile until you have crossed the river"