At what point should one take action to prevent frost damage? When
the forecast calls for temperatures to dip to 32 or below? Or should
you play it safe and take action any time the temps dip below 40?

Also, is spraying plants with water for frost prevention as effective
as covering them with material?
And at what point in the evening should preventative measures be
taken? Right after sundown, or is late in the evening ok?

Fleemo wrote:

At what point should one take action to prevent frost damage? When
the forecast calls for temperatures to dip to 32 or below? Or should
you play it safe and take action any time the temps dip below 40?

Also, is spraying plants with water for frost prevention as effective
as covering them with material?
And at what point in the evening should preventative measures be
taken? Right after sundown, or is late in the evening ok?





It depends. What are you trying to protect?

Some plants will show damage with air temperatures of 35F or below with
clear skies at night. Radiation cooling will produce local frost and
damage the plant. Basil is the best example of this.

Other plants will take temperatures down to 20F with no damage. Lettuce
is one of these (not all varieties however -- the red edge seem to do
better than green lettuce).

If you are dealing with radiation cooling (air temperatures above 32F)
you can cover the plants. If you do this, support the cover so that it
doesn't touch the plant. The cover will get cold and can damage the
plant where it touches.

If you are dealing with really tender plants such as basil, a water
spray won't provide much protection, since it will freeze. If the
temperature is really marginal it might help, but such plants really
don't like the low temperatures and may just decide to die anyway.

The way a water spray works is that water requires a certain amount of
energy to change from a solid to a liquid. It gives off this energy when
it changes from a liquid to a solid. The water releases this energy,
called the "heat of fusion" when it freezes. This means that in the
process of freezing, while you have a mixture of ice and water, the
local temperature is kept at 32F. Once all the water is frozen, the
local temperature will go lower. This is why you have to keep spraying
liquid water. However, the best you can do is to keep the local
temperature from going below 32F.

In the case of the cold tolerant plants, their fluids have a lot of
dissolved solids (sugars, starches, various nutrients). The dissolved
solids lower the freezing point of the liquid below 32F. The plant will
eventually freeze, however, and since the plant fluids are largely
water, the water will expand on freezing and break the cell walls,
damaging the plant.

As far as the time of night to apply protective measures, unless the
temperature is really dropping rapidly, late in the evening is OK. The
coldest part of the night is usually just before dawn. However, if you
have a rapidly moving cold front coming through it could drop below
freezing quickly (even during the daytime hours).

It's a bit late in the winter (northern hemisphere) to worry about frost
protection.

"Fleemo" wrote in message
om...
At what point should one take action to prevent frost damage? When
the forecast calls for temperatures to dip to 32 or below? Or should
you play it safe and take action any time the temps dip below 40?
///////////////////////////////////////////////////////
In a way you need to act a little bit like a weather man...for myself I tend
to take protective action whenever the night is due to be "clear sky, and
wind free" with the temp. being forecasted below 40 degrees........usually I
do not get caught this way...many a time have seen the forecast being around
a low of 38 and a heavy frost has resulted...HW.

Fleemo wrote:

At what point should one take action to prevent frost damage? When
the forecast calls for temperatures to dip to 32 or below? Or should
you play it safe and take action any time the temps dip below 40?

Also, is spraying plants with water for frost prevention as effective
as covering them with material?
And at what point in the evening should preventative measures be
taken? Right after sundown, or is late in the evening ok?

Depends on what you are needing to protect. Many early blooming plants
can have their flower buds damaged by a late hard frost - camellias for
example - but many other cold-sensitive plants will not survive a late
frost regardless of the protection you provide. Annuals like basil,
coleus and impatiens would be included here. Most perennials and woodies
will withstand a pretty good late frost without protection if they are
hardy for your zone. They might suffer some minor foliar damage, but the
roots should be unaffected. If you are concerned, try covering with remay
(aka harvest cloth) - this will ensure temps under the cloth are at least
5 degrees above the air temp.

I am a good bit north of you and we have had clear skies and frosts for
the last few days. I protect nothing in my garden - it must stand on its
own - and although many plants are already budding/blooming due to our
unseasonably mild winter, nothing appears to be any the worse for wear.

We gardeners tend to worry a bit unnecessarily sometimes - I can't
imagine that frosts in the Sacramento area could be too terrible at this
late date.

pam - gardengal

On Fri, 07 Feb 2003 00:41:08 GMT, Pam wrote:

We gardeners tend to worry a bit unnecessarily sometimes - I can't
imagine that frosts in the Sacramento area could be too terrible at this
late date.

pam - gardengal


Much of the SW will get the hardest frost of the past winter tonight.
Imagine that.



Regards,

tomj

Much of the SW will get the hardest frost of the past winter tonight.

Indeed. What has been an extremely mild winter has suddenly turned
quite cold. We've barely dipped below 40 all winter, but every night
this week has flirted with the freezing mark. I had a lovely clump of
nasturtium that was flourishing until the night before last. Now it's
history.

I had thought that a sprinkling of water would help to get the plants
through the night, but I guess I'd better go back to draping sheets
all over the yard.

Can anyone point me to a list of plants that are particularly cold
sensative (such as nasturtium, basil, impatiens)? I don't always get
around to covering ALL my plants, and would like to know which ones I
should focus on and which stand a better chance of braving the cold.

Thanks for all the input here folks.

In article , Dwight Sipler
writes:

It's a bit late in the winter (northern hemisphere) to worry about frost
protection.



Actually not. We in northern Calif. have had very light frosts, if any, so
far.
The tender zinnias and ageratum are gone,but some things linger.
Last night was the first hard frost.....it was 28 degrees at 7:00 am today,
2-8.
The nasturtiums are mostly mush. I don't bother to protect them. The cannas
leaves will be brown, but the callas are fine. As is Abutilon.
Each tiny part of the Sedum acre is outlined in white, it's quite lovely.
The almond growers turned on the sprinklers to protect the early bloom.
Bloom is about 2 weeks early. It is a winter wonderland with all the icicles
hanging on the trees.

Emilie
NorCal zone 8

In article , Tom Jaszewski
writes:

On Fri, 07 Feb 2003 00:41:08 GMT, Pam wrote:

We gardeners tend to worry a bit unnecessarily sometimes - I can't
imagine that frosts in the Sacramento area could be too terrible at this
late date.

pam - gardengal


Much of the SW will get the hardest frost of the past winter tonight.
Imagine that.



Regards,

tomj


Yep. Last night's temp was 28 degrees. It had only been to 32 before that.
'Tho I am not exactly in the Southwest; but not the Northwest either. Does
that make me the Mid west???
Emilie
NorCal

"Fleemo" wrote in message
om...
At what point should one take action to prevent frost damage? When
the forecast calls for temperatures to dip to 32 or below? Or should
you play it safe and take action any time the temps dip below 40?

Play it safe. We had a minimum at 34 degrees on Wednesday morning (low
desert). I had a frost blanket over the tomatoes but it blew off on
one corner and one of the plants' leaves froze. It may recover but will
now take more time to produce fruit than the others and will probably
never be as healthy. 32 degrees for freezing is not an absolute. It
can also depend on air density (less dense in the desert), humidity and
several other ambient conditions. We sometimes get light freezes with
no white frost deposits because of the low humidity. We never need to
protect leafy crops or root crops but occasionally the frost-tender
varieties like tomatoes, peppers, corn, etc. need protection

Also, is spraying plants with water for frost prevention as effective
as covering them with material?

I believe a frost blanket is best. Water droplets freezing on the
leaves of frost tender plants can't be good for them.

And at what point in the evening should preventative measures be
taken? Right after sundown, or is late in the evening ok?

In our area, the coolest time of day is at sunup. I usually cover mine
tomatoes at sundown to help hold in the heat. But any time it is at or
near freezing and dropping is okay if you are only worried about frost
and not concerned about keeping the plants warm.

Note that my perspective is from the low desert and may not apply
everywhere. For some practical tips, see:
http://ag.arizona.edu/pubs/garden/az1002.pdf

Olin (Near Phoenix AZ)

Olin, are you really growing tomatoes already??? Do they live through
the winter in your zone, or did you just plant them outside rescently?
Lucky dog.

Thanks for all the input here folks. I'm sure my plants thank you all
for it.

-Fleemo

"Fleemo" wrote in message
om...
Olin, are you really growing tomatoes already??? Do they live through
the winter in your zone, or did you just plant them outside rescently?


Planted mine on Jan 1. Four of the first 12 plants have small green
fruit (2 Sun Gold, 1 Early Girl and 1 Beefy Boy). Spring tomatoes are
usually transplanted from Jan 1 thru Mar 1. The earlier plantings need
lots more TLC but have a better chance of getting an acceptable yield
before the hot, hot summer weather.. The Mar 1 tomatoes are a bit iffy,
especially if we have an early summer. Sometimes they will live through
the summer and bear again in the fall but the fruit isn't as good or as
plentiful.

The second tomato crop is usually transplanted from late July through
October 1. The earlier plantings also need lots more TLC but it's for
protection from the blazing hot sun. The later plantings will usually
set fruit but it often will not ripen until February because of our
short days and cooler weather. But this year's Jan was so warm, many
gardeners had fresh ripe tomatoes since last month from their fall
planting.

Olin