In the Garden Articles

Frost Damage

by Joan S. Bolton

How's your garden holding up?

If it's like mine, you lost at least a few plants to last week's frost and freezing temperatures. The cold laid waste to countless citrus trees, avocados, queen palms, jasmine, lantana, lavender, flowering vines and other ornamentals across the Central Coast.

But procrastination may have helped a few of my plants. I hadn't yet gotten to my annual pruning of Mexican sage and heliotrope. The leggy overgrowth helped to insulate the interior of the plants. So while the bulk looks horrible, a few green leaves buried beneath indicate that they're not dead to their roots.

Signs of life may not be as apparent on other damaged plants. Depending on the extent, some trees might not sprout new growth for several months. You can scratch the bark with a fingernail to detect any green or cream-colored wood. But this early, that's not a reliable indicator.

It's also too early to tally your casualties or prune the dead stuff.

Those spoiled leaves and branches will continue to protect any life left within during the rest of winter. Cutting now will unnecessarily expose vulnerable tissue and stimulate new growth that's highly susceptible to cold.

"As long as there's a cold threat, I'm advocating not to cut back your plants," said Bob Blokdyk, owner of Windmill Nursery in Buellton. "You don't want to encourage new growth. That growth is going to be soft and the plant is going to get hurt even more. The roots only have so much energy to push out growth. You want the roots to conserve that energy. Don't fertilize and don't prune."

Granted, it's tempting to remove the uglies immediately. But it really is best to wait. Back in the freeze of 1990, one of my avocado trees didn't show green until June. Had I pruned limbs that appeared to be dead earlier, I wouldn't have had much of a tree left.

What to Do Now

While pruning is off the table, you can continue to protect your plants.

First, keep your plants well watered. We've had little rain and low humidity: your soil may be surprisingly dry for this time of year. Frost damage occurs when tiny ice crystals form on the leaves, sucking out moisture from the tissue. If your plants are already dehydrated, they're more likely to succumb.

Also, moist soil holds more heat during the day, which means it transfers more heat to the plants at night. Apply a loose mulch of bark, hay or straw around your plants to retain the moisture longer.

Next, cover any valuable, susceptible plants, such as palms, citrus trees and tender perennials, with a bed sheet, lightweight blanket, plastic, cardboard or old newspapers whenever frost or freezing temperatures are expected. Cover the plants before the temperature drops below 40(F. Make sure the material rests flush on the ground to prevent heavy, cold air from creeping in underneath.

Remove the covers when the temperature warms up the following morning. If you don't, the covers -- especially clear plastic -- can trap too much daytime heat and turn the space underneath into a hothouse.

The downside of this method is that you have to cover and uncover your plants every day. It's a hassle. You might not be home in time for the night-time covering or the mid-morning unveiling. And the constant on-and-off can damage otherwise-unscathed leaves.

Blokdyk advises wrapping favored trees and shrubs with frost cloth instead. He said the polyethylene fabric is light, doesn't weigh down branches, allows water vapor to pass through, is rated to 4 to 8 degrees and can be left on for months.

"You don't have to uncover it," he said. "We actually cover certain plants all winter. Like the agapanthus, which doesn't take our winter cold. We uncover the plants in the spring and they look great."

Blokdyk suggested taking a step further by incorporating Christmas lights.

"The lights put out a little bit of heat energy," he said. "This works well on small citrus trees. Then over the top, you put on the frost cloth. It's kind of like wrapping it in a blanket, and putting a slight amount of heat inside."

Some folks swear by hosing down their plants late in the evening or even running sprinklers all night. The idea behind this is that water releases a bit of heat energy as it freezes. The extra dash of heat can be just enough to keep the plants alive.

But it's a complicated dance between temperature and humidity, and if you don't apply enough water to balance out heat lost to evaporation, it can create a disaster.

Commercial growers also use heaters and wind machines. The heaters boost the ground temperature by a few degrees. The powerful wind machines push the cold, ground-hugging air up, which allows slightly warmer air above to slide in. Don't try this at home: your summer-cooling fan won't have enough oomph to generate the same effect.

A Bleak Spring?

Even a full day of preparation with a team of five workers wasn't enough to save every plant at Bob Blokdyk's Windmill Nursery in Buellton from five consecutive nights of temperatures in the teens last week.

"We covered up plants. We greenhoused some items... We sprayed all our roses and deciduous trees with Wilt-Pruf, a paraffin product. We thought we were prepared," Blokdyk said. "(But) that's Mother Nature. She throws us a curve now and then."

Among those hardest hit were Blokdyk's vines.

"A lot of our vines, hardenbergias, jasmines, were just getting ready to bloom. They only go down to 20 degrees safely. They were under a cold frame. It's just that the cold was too long," he said. "They're not completely dead. There's still a green stem. But if you walk up to them, the leaves will fall off."

Unfortunately, Blokdyk said, it may take six months for many of the damaged plants to look good enough to sell.

Blokdyk said he's talked with growers throughout the Southwest who have suffered similar losses.

"Their plants may not be dead, but they're going to lose their spring crop. Customers are going to be ready to buy early, but there will be a lot less available," he said. "Getting replacements is going to be difficult. It's kind of a double whammy."

If You've Already Pruned

If you've already pruned frost damage, you'll need to take extra steps to protect your plants. Every point where you made a cut is more vulnerable to cold, and any new growth that results can be literally nipped in the bud by frost.

If all that's left is a stub or a few stems, water thoroughly, then mound up a layer of loose straw, shredded leaves or bark over the top of the plant, up to 6 to 8 inches high. Monitor the soil moisture until spring.

If you've cut back limbs, cover the entire tree and secure the bottom around the trunk so the cold can't seep in. You can leave frost cloth on until spring. But sheets, blankets or plastic will have to come off daily. Keep the tree well watered. Deep soaks every week are more effective than frequent, shallow watering.

Seeds of Wisdom

Most frost damage results in dried-up, brown or gray flowers, buds and leaves. But some tender plants -- including succulents such as jade, kalanchoe and aloe -- puddle into black mush. This happens when the moisture inside the leaves and stems freezes, expands and ruptures the tissues.

After night-time temperatures warm up, remove the slushy, black leaves. Wait until spring to see if any new life sprouts from the base.