Frost
protection in the Sacramento Valley
You don't need to worry about most of your plants during a
normal frosty night here!
Some plants should already be inside, or under an overhang in a south or
east-facing exposure. Examples include jade plants, bougainvillea, hibiscus, Mandevilla
(pink-flowered forms). Any house plants you've kept outside during the summer
should be in by now!
Many
subtropical plants will show slight to moderate damage in a normal frost, but
will recover quickly in spring: lantana, fuchsia, verbena, Limonium (statice),
passifloras (passion flower vines; some fruiting types are more tender), purple
potato vine (Solanum rantonnetii), and others may be damaged by frosts
or freezing weather. They can simply be cut back in the spring and they will
regrow vigorously with the return of warm weather. Many were severely damaged
in 1990, 1998, and January Õ07, but most recovered even from those very low
temperatures.
Most landscape plants need no winter
protection even in a hard freeze here: azaleas, camellias, gardenias, roses
will be fine.
Plant protection tips--
-- Use microclimates: move container plants to sheltered places.
Reflected and retained heat from warm walls (east or south facing)
and cement walks will provide several degrees of protection. Fences and walls
can protect plants from the drying effect of cold winter winds.
-- Make sure all plants, especially those in containers, are well
watered.
If dry soil freezes, it will pull moisture from the roots, causing
them damage. If the soil is moist it can freeze without harming roots.
-- Lightweight spun plastic fabrics are most effective.
Usually sold as floating row covers or seedling blankets, these
can simply be draped over the plant and wonÕt damage the foliage. Anchor in
case of wind; metal landscape pins can hold the fabric in place.
-- Christmas lights.
Large-bulb lights strung over or through plants are very
successful, even with temperatures in the teens, especially if the plant is
also covered with spun plastic to trap the warmth. . Landscape lighting and
portable shop lights also work. Be sure to leave the lights on all night! The
coldest temperatures are just before dawn.
-- More extreme measures.
Blankets and tarps can be used in a pinch during a major freeze,
but if you use any material that isn't clear you need to remove it during the
day. Plants can't live without light! Wrapping the trunk with burlap can help
prevent major damage in a severe freeze.
What about Citrus trees?
Mary Helen Seeger is co-owner of Four Winds Growers, a wholesale
citrus nursery located in Fremont and Winters. "There is no need to panic
with a few hours of temperatures in the high 20's such as occurs during a
normal radiation frost," says Seeger. "The Christmas lights do wonders in the low twenties, and help prevent severe
damage in the rare occasions when temperatures are in the teens."
á Potential cold
damage is a combination of temperature (how cold) and time (for how long).
Brief dips to the mid 20's will not damage most citrus. Prolonged temperatures
in the teens caused much damage in 1990 and 1998.
á Limes and
lemons are the most sensitive, needing some winter protection in colder
locales. Other citrus are fairly hardy once established. Kumquats and mandarins
are especially cold hardy.
á Most citrus fruit will be
damaged at about 26 degrees. Don't pick them unless you have to, because the
fruit won't get any sweeter once it is off the tree. Lemons and limes can be
juiced and frozen in ice cube trays. The fruit on the outside branches of the
tree will be most vulnerable, so pick that first if necessary. Tender new
growth will be killed, but this isn't harmful to the tree. Significant damage
to leaves and branches occurs in the low 20Õs and teens.
Frost or Freeze?
What's the difference between a frost and a freeze?
Frost occurs on a clear, still night, as heat radiates from
surfaces (car windows, open fields, etc.) to the sky. The temperature drops
below 32 degrees, and water vapor freezes on those surfaces. The temperature
usually won't go much below freezing for a while, because some energy is
released as the water freezes. Frost can be very local, with visible frost out
in open areas but none where the surface is covered.
Most plants that aren't truly tropical can go 2 - 3 degrees below
freezing with no problem. Heat will be trapped by any overhang, so tender
plants can be protected up against the house. Clouds or fog prevent frost by
trapping heat that is being radiated to the sky.
We get several frosty nights here every winter, and they are
nothing to worry about.
A freeze is when cold, Arctic air moves into the region. Local
news stations give us warning as these cold fronts bear down from the Gulf of
Alaska. The air is muchcolder than freezing, there is wind, and the
humidity is very low. Much of the damage we see on plants after a freeze is
from desiccation--severe drying of the foliage and stems. An overhang provides
less protection; sheltered plants may even need to come indoors, or multiple
protection measures may be necessary.
In the event of a major regional freeze such as we experienced in
1990, 1998, and January 2007, our efforts turn away from saving fruit and
foliage, and we focus on simply trying to keep the plants alive.
© 2017 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
www.redwoodbarn.com
Feel free to copy and distribute this article with attribution to this author.
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