Marin County
University of California
Marin County

Frost tip: Don't touch your plants

Horticulturist Pavel Svihra, holding a damaged plant, teaches a class on frost damage and prevention to a group of master gardeners at the University of California Cooperative Extension in Novato. (IJ photo/Frankie Frost)

Nancy Isles Nation
Marin Independent Journal link to article

1/17/07

If you're itching to get outside and do something about those frostbitten plants in your yard, take the advice of a master gardener and relax - be patient with your impatiens.

After four nights of frost, plants and trees in Marin are suffering and property owners are anxious about the viability of their greenery - whether they are concerned about aesthetics or their hard work and investment.

On Tuesday, about 35 volunteer master gardeners with the University of California Cooperative Extension in Novato were primed for giving advice to homeowners by Pavel Svihra, the university's horticulture adviser emeritus.

Svihra said that, in the past four days, weather conditions that have brought clear skies to the county have been dangerous to plants because the morning sun quickly defrosts ice that has developed on plants overnight.

"This is very devastating for the plants," Svihra said, adding that wind makes matters even worse. "It desiccates plants - stressed plants are more susceptible to the frost."

The UC Cooperative Extension is an agricultural advisory service that is paid for in part by county taxpayers. It includes about 260 volunteers who answer phones to provide advice to homeowners.

"We encourage homeowners to use healthy practices forgoing toxic chemicals," said the extension's Glenn Smith.

According to Svihra, Northern California has a history of frosts of concern every nine to 12 years. It is more severe inland than in coastal counties like Marin because the temperatures are likely to get colder and destroy crops such as citrus trees.

While many plants are capable of withstanding temperatures as low as 28 degrees, Svihra said Californians have taken to planting problematic exotics.

"We love to plant for beauty and enjoyment plants that don't belong here," Svihra said.

If you must, he said, plant more susceptible plants on the south side of your property.

If you see damage to your plants now, leave them be.

"Wait until new growth starts, which marks exactly where the freeze damage stops," Svihra said. "Don't touch plants until the frost is over."

He cautioned that gardeners should not overwater or overfertilize prior to winter's onset because it can encourage tender growth to appear, and that growth is easily damaged.

Overwatering also can invite mold to attack plants and destroy them.

Answering questions from the master gardeners, Svihra said misting plants with a spray bottle early in the morning - at 5 or 6 a.m. - can insulate them from major damage.

But patience is the most important rule of thumb.

"It may be ugly, but wait until new buds start to open," Svihra said. "They will determine how deeply the frost permeated."

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SAY GOODBYE TO YOUR ANNUALS

Here are a few tips on keeping your plants safe:

1. Water. Soil around plants should be moist, especially in containers. Moist soil retains heat and protects roots better than dry soil.

2. Move any at-risk container plants under a porch roof or eaves, or into a garage.

3. Shelter plants in the ground with burlap, plastic sheeting or semi-transparent floating row cover material secured on stakes so that the covering does not touch the leaves. Especially at risk are subtropical plants such as bougainvillea, hibiscus and some of the tender jasmines.

4. Spray sensitive plants or citrus with "Cloud Cover" or any brand of anti-transpirant spray at least a few hours before frost is expected to provide a couple of degrees of protection.

AFTER THE FROST

Don't prune damaged plants right away. Pruning may encourage new growth prematurely and the plant could suffer more damage in a subsequent cold snap. Although the plant may appear dead - with black leaves such as a frozen citrus - don't give up on it just yet. New growth may appear in the spring, and then cut off only what is necessary.

STILL NEED HELP?

For advice, call the UC Cooperative Extension at 499-4204 from 8:30 a.m. to noon and from 1 to 4:30 p.m. weekdays. Specimens may be taken to extension offices at 1682 Novato Blvd. in Novato.

Webmaster Email: banielsen@ucanr.edu