The weather forecasters in this area certainly
pay homage to the old saying that "only a fool or a newcomer
will try to predict Texas weather." I fear that these
prognosticators of the climate will have frost on their eyebrows
before they will sound the protection alert to home gardeners.
To remedy this situation, I have decided to tell you when
the first frost will occur!
After careful examination of the thickness
of animal fur, the sharpness of porcupine spines and quantities
of mesquite pods correlated meticulously with moon signs,
sun spots and migratory habits of the gray?backed pillbug,
I have decided that the first killing frost for South Central
Texas WILL occur in November. A really hard freeze will
occur in December. Freeze denotes the condition where air
temperature of surface objects (i.e. plants) falls below
32 degrees F. (0 degrees C). Frost is simply the occurrence
of condensate freezing on exposed surfaces. For frost to
be deposited, the surface temperature of an object must
drop below the dew point of the surrounding air. A freeze
can occur in a dry air mass without frost being deposited.
Advective freezes occur when a cold air
mass blows in; this is the typical "Norther".
The temperature of this air is below freezing at ground
level with windy conditions, which makes protection of tender
plant material difficult. A homeowner may cover plants with
straw or similar material, or with a stout container like
a trash can. The degree of protection would depend on the
insulating capacity of the cover. If you have followed the
recommended practice of caging tomatoes, you may cover these
cages with large plastic garbage bags to protect the plants
within the cages. The cage will act as the supporting structure.
If you do not have cages, you might want
to erect a supporting structure. Be certain these cages
or structures are well secured or anchored since high winds
usually accompany the bad northers. If cages covered with
garbage bags should blow over during the night, not only
will the plant freeze, but it also will be pulled out of
the ground by the roots. In this instance, the remedy for
protection may be worse than the frost damage. Be careful
not to remove your covers too early on the morning following
the frost. If your plants have gotten slightly frosted during
the night, a slow "thawing" can prevent extensive
damage. Also, rapid exposure to cold temperatures is rough
on plants just as it is on folks. Take your time!
A radiation freeze is a different matter.
All objects (houses, soil, plants, etc.) radiate heat in
all directions; the amount of heat radiated is proportional
to the object's temperature. Conversely, all objects absorb
heat given off by their surroundings. In the case at hand,
a plant exchanges radiant heat with the sky. During the
day, the input from the sun is greater than the radiant
loss from the plants; therefore, the plant and its surroundings
heat up. After sundown the energy flow reverses and the
plant loses heat to the sky.
On clear nights, the radiative cooling
of plants can be substantial; in fact, a plant can get considerably
cooler than the air surrounding it. Even if the day has
been mild, enough radiative cooling can take place at night
to freeze plant tissues. Significant freeze damage can occur
even when the air temperature never gets to 32 degrees whether
or not frost is deposited depends on the moisture level
of the air. Classic radiation freeze conditions are clear
sky and calm, dry air. Cloudy conditions reduce the amount
of radiative loss to the sky. Any appreciable wind movement
keeps plant tissue from cooling below the temperature of
the surrounding air.
One natural control of frost injury is
elimination of bacteria on the leaf surface of plants. Dr.
Steven Lindow, University of California?Berkeley, has found
that three species of bacteria are active ice nuclei (catalysts
for ice formation) at temperatures only slightly below freezing
and initiate the ice formation that is required for frost
damage. Furthermore, Lindow has found that these bacteria
live on leaf surfaces of healthy plants in large numbers,
and the amount of frost damage increases as numbers of ice
nucleation?active bacteria increase on a given plant. A
reduction in bacteria population results in a corresponding
decrease in frost injury. What this means is that an application
of a bactericide spray, such as streptomycin (sold as Agri?Strep
or Fertilome Fireblight spray) will provide cold protection
to some plants to temperatures as low as 27 degrees F. Researchers
have found that the best spray solution to use is 100 ppm
of streptomycin (approximately one tablespoon) and two tablespoons
of table salt per gallon. Spray to runoff or thoroughly
wet the foliage at least 24 to 36 hours before the frost
occurs. A treatment should be effective for several weeks.
The use of bactericide?fungicide product will also control
foliage diseases so its worth a try. Keep the streptomycin;
it will be useful to prevent fireblight on apples and pears
Another thing that you might try is an
anti?transpirant spray such as Wiltproof or Cloud Cover.
These reportedly provide a certain degree of protection.
Remember to be scientific in your application. This means
that certain plants should be sprayed with streptomycin
and salt, others with the anti?transpirant, some with both
and some with nothing. Then after the freeze we can evaluate
the effectiveness of the treatments. I have mentioned that
the streptomycin can be used this spring to prevent fireblight;
the anti?transpirant can be used even sooner to keep your
Christmas tree fresher for a longer period of time. So both
products have an alternate use.
When should the frost protection be used
and on which vegetables? I wholeheartedly rely on our weatherman
and subtract a degree factor of eight for safety. For instance,
if your favorite weatherman predicts a low of 36 degrees,
you had better cover the plants. This applies especially
to those living in the northern areas of our city. If the
weatherman is right and the temperature only falls to 36,
you have merely experienced a trial run. If Parsons is right
and the temperature dips to below freezing, you owe the
vegetable specialist a Christmas tomato.
Vegetables which are frost tolerant include
asparagus, beets, broccoli, Brussels sprouts, cabbage, carrot,
cauliflower, celery, chard (Swiss), chicory, Chinese cabbage,
chive, collard, endive, garlic, horse?radish, kale, kohlrabi,
lettuce, mustard, onion, pak?choi, parsley, parsnip, pea,
potato, radish, rhubarb, rutabaga, salsify, shallot, spinach,
Vegetables which are damaged by frost include:
bean, bean (lima), chayote, corn, cowpea (Southern pea),
cucumber, eggplant, muskmelon, New Zealand spinach, okra,
pepper, pumpkin, soybean, summer squash, sweet potato, tomato,
watermelon, winter squash.
So prepare yourself ?the cold is upon us!