After the Freeze
From the Davis Enterprise, January 25,2007
The freeze of 2007 is now one
for the history books in Yolo County. Although temperatures didnÕt stay as cold
for as long as the freeze of 1990, nor did we reach any absolute low
temperature records, we had 13 consecutive mornings below freezing in Davis January
8 through 21, tying the previous record set in December 1990.
This is all in addition to
the shorter cold snap we had December 17 – 20, which did a fair bit of
damage in gardens locally. In fact, weÕd
already had 13 days of frost by December 31!
Some notable data from this
spell of cold weather:
Temperatures in western Yolo
and eastern Solano counties ranged from 1 – 9 degrees below the official
readings in Sacramento. On the coldest morning, January 14, Davis was 20
degrees, Dixon was 17. Winters was 18 degrees. Sacramento came in at 25.
Gardeners should be
particularly concerned when temperatures drop below 25, as that is when
significant plant damage can occur. Davis has had 3 mornings below 25, Dixon
has had 6.
Humidity through this freeze
has been very low. On the coldest day the humidity dropped to 16%, and only
reached 52% at night (humidity is usually in the 90%+ range at night).
Esparto is the banana belt of
Yolo county, with morning lows 3 – 8 degrees or more above Davis, only
dropping below 25 on the coldest morning (Jan. 14), and with only four nights
of freezing weather through the entire period. A quick look at the topography
of northeastern Yolo County will show you how winter heat is trapped in the
Capay Valley. I foresee a new real estate boom: winter condos in Esparto.
As in 1998, CaliforniaÕs
navel orange crop has been destroyed. Preliminary damage estimates range from
75 – 90%. The freeze was statewide, damaging avocadoes, cut flower crops,
and the first crops of strawberries and artichokes in coastal fields. Damage to
nursery stock was extensive in Southern California, where many of our favorite
subtropical plants are grown. These growers supply many of the larger home
improvement chains. Damage to nurseries in the north of the state will delay
availability of some plant material until late spring or summer. Growers will
have to cut back damaged plants, and wait for a flush of new growth, before
they will be ready to sell.
Unfortunately, the damage to oranges and lemons is not
obvious by looking at the fruit, and home gardeners may be in for some
unpleasant surprises. Though there may be ÔburntÕ look on the exposed part of
the peel, the damage is to the quality of the juice. As you harvest you may
notice off flavors. The fruit will definitely not keep well, as spoilage will
progress rapidly at indoor temperatures. If you havenÕt harvested already,
sample some fruit and use them as soon as possible.
So what should home gardeners
do about the damage in the landscape?
The simplest answer is Ôwait
and see.Õ The full extent of damage is not yet apparent, and continued frosty
nights may continue to kill leaves and stems.
á Continue to provide protection. Floating row covers
(aka Ôseedling blanketsÕ) appear to have been the most effective in preventing
damage. Draped over the plants, or wrapped around them to create ghostly plant
pupae, these trapped enough heat to prevent serious injury. Since they allow
light to penetrate by day, they act as individual greenhouses, getting surprisingly
warm during the day. Leave them on the plants for as long as frost is in the
forecast.
á DonÕt cut anything back yet. Open cut wounds are
avenues for further cold damage, and the dead leaves hanging on the plant
actually provide a small measure of protection simply by ÔcloakingÕ the
remaining stems and leaves. Wait until we are reliably out of danger of
continued frost. Even better, wait until the plant starts to
grow—probably in late March or early April. Then youÕll know how hard to
prune: cut back to the new growth. In many cases a severe pruning will be
appropriate, but itÕs wise to ask a professional first.
á Keep container plants watered. Desiccation is the
greatest risk during freezing weather. Plants in the ground probably donÕt need
water, except those you planted within the last 2 – 3 months. Although we
are way behind on rainfall, there is enough moisture in the soil from the early
winter rains that IÕm not concerned about established plants. Exceptions would
include plants under overhangs, where winter rainfall didnÕt penetrate.
á Your irrigation systems will need your attention. My
pipes froze on January 14 and 15, and when the water finally came back through
the house there was a bunch of murky solid matter at the head which promptly
plugged my sink and shower heads. Freezing the water had precipitated out the
copious salts in our groundwater – calcium and boron, mostly. You can
imagine what these solids will do to your drip irrigation emitters and
sprinkler heads. I strongly recommend flushing out your sprinkler and drip
systems before you turn them on for the season!
á Some plants that I expect will not recover include:
Australian tree ferns
Begonias
Bougainvillea
Hibiscus (tropical)
Mandevilla (evergreen types)
á Serious damage, but likely to resprout:
Avocadoes
Brugmansia (AngelÕs trumpet)
Bananas (mostly killed to the
ground)
Citrus trees (limes and young
trees are most vulnerable)
Hardenbergia (Lilac
vine—there wonÕt be any of the lovely purple flowers this winter!)
Jasmine (true jasmine; Star
jasmine is fine).
Palms, particularly Queen
palm (outer fronds will dry up and look dead, but the growing point is
protected inside the center of the tree).
Pandorea (Bower vine,
considerable top damage)
Passifloras (cut Ôem to the
ground in late spring; theyÕll be back)
Potato vines (the purple ones
look worse than white, but mine recovered in 1990)
Red trumpet vines (severely
damaged, unlikely to flower this summer)
Any decision about replacing
plants should wait until weÕve had several weeks of warm weather. Subtropicals
can be surprisingly resilient, and may resprout as late as May. So donÕt be in
a rush to pull them out. (Keep in mind that nurseries arenÕt likely to have
replacement plants until summer anyway). If youÕre curious about a woody shrub
or vine, just scratch the bark with your thumbnail: if itÕs still green
underneath, itÕs still alive. A good rule of thumb is that subtropicals start
to grow (or regrow) when itÕs tomato-planting season.
We seem to have these freezes
on eight year cycles: December 1990, December 1998, January 2007. Keep the
Christmas lights and seedling blankets handy for 2014É.
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