By Cindy Watter, U. C. Master Gardener of Napa County
One of the attractions of my house, when I first saw it for sale some decades ago, was a fragrant, lush Meyer lemon tree, abloom in the side yard. Unfortunately, by the time I moved in, the Great Blue Norther of 90/91 had transformed it into a blackened mass of lifeless twigs and shriveled leaves.
The previous owners had neglected to cover it at night, and the unusually cold weather that winter had done its malign work, killing the tree. It actually looked as if it had been scorched, not frozen. I learned that the plant cells had solidified in the cold, which meant that the nutrition cycle had been blocked. The lemon tree appeared deflated, which was exactly how I felt at the time.
The best way to protect your plants during an unusual cold spell is through preparation. Assume it will freeze sometime this winter. (It only takes one night to do major damage.) Pay attention to weather reports. Identify which plants need protection. Assemble a collection of old sheets, blankets, towels, burlap, cardboard boxes, baskets and/or buckets. Do it now to avoid the horrid midnight rush to save the avocado (when it's probably too late anyway).
What plants will need attention? Young fruit trees with thin bark, avocado trees and citrus trees are the main candidates in Napa Valley. Certain tender shrubs, such as brugmansia, fuchsia, mandevilla, daphne and bougainvillea should be covered. Some cacti and succulents need protection. If you have plantings in a lower elevation of your yard, these plants should certainly be protected, as those parts of a yard are always a few degrees colder than the rest of it.
Water the plants before you cover them, which should be before dusk (except for succulents). Some of the water will evaporate during the night and warm the surrounding air.
For small plants, you can fill old plastic milk jugs with water, which will insulate the plants a bit, and then use those vessels to support a draped cloth.
Small plants will do fine with an overturned bucket, cardboard box or basket for protection. If you have a lot of small potted plants, move them to a protected spot or next to a wall. You can also protect small plants by covering them with mulch.
If you use a sheet or a blanket as a cover, it shouldn't touch the plant. You can build a frame to support the cloth, or create your own supports with lawn furniture, clothes drying racks, trellises or bean poles. If the cloth touches the plant, it can transmit cold, so use a frame. Make sure the cloth reaches the ground, for better insulation. Remove the cloth in the morning, after the air warms up.
You can wrap young tree trunks with burlap or old blankets or towels for insulation.
Nurseries sell plant covers in all sizes and shapes, including row covers. They are made of a nonwoven synthetic, and they allow light to penetrate so you can leave them on during the day. This fabric—similar to the interfacing used by home sewing enthusiasts—can touch a plant's leaves without doing harm.
If the worst happens and your plant freezes, don't lose hope. It just might recover. I thought I had killed two large brugmansia shrubs last winter. A surprise freeze had left them drooping and shriveled.
I consulted Sunset's Western Garden Book and learned that, instead of hacking the shrubs down to the ground or throwing them out, I should wait until spring to see if any new growth occurred. And it did!
At that point, I pruned the brugmansia down to the green leaves, put them in large pots (so I could move them near the house in the winter) and saw them put forth spectacular peach-colored trumpet-shaped flowers in late summer. They are so sturdy they even survived a walnut limb landing on them and being blown over by the windstorm that preceded the October wildfires.
When spring returns, rethink some of your plant placement. Perhaps you have citrus trees in planters. You could put the planters on wheels and roll the trees to a sheltered spot during cold spells. Maybe you should move plants that are in sunken areas of your yard.
A fragile plant can be placed against a south-facing wall, and the warmth that radiates from the wall will help the plant get through the winter. I have noticed how many bougainvillea are trained against south walls in Napa Valley. That's where my new lemon tree is, and it has survived several cold spells.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.
Citrus trees are evergreen, not deciduous, and never go fully dormant. As a result, they cannot withstand extremely low temperatures as well as deciduous trees, which are better prepared to handle cold weather.
I thought I had followed good preventive measures for my own trees by covering them with tarps and watering them deeply before the first freeze, but they still suffered significant damage. With near perfect hindsight, I realize that I should also have strung the trees with lights of at least 15watts to provide a little warmth.
After a brief mourning period, it was time to move on. The old English proverb that “necessity is the mother of invention” came to mind as I surveyed the ripe fruit on the trees.
A quick Internet search revealed that citrus juice can be canned and the process is easy. I already had canning jars and lids, a water-bath canner and a juicer so I was ready to go. I sterilized the jars and lids, squeezed dozens of lemons and limes and then heated the juice to 190°F for five minutes. I poured the hot juice into the sterilized jars, sealed the jars with lids and bands and processed them in the boiling- water bath for 15 minutes. Now I have enough canned lemon and lime juice to get me through the coming year. If you want to juice your frost-compromised citrus, do it sooner rather than later as the damaged fruit will dry out over time.
Today, when I look at my citrus trees, my first reaction is to do something to help them recover. However, the wise gardener waits until the extent of the damage becomes apparent. Prune too soon and you may remove parts of the tree that could recover if left alone.
Pruning too early may also encourage new growth that is susceptible to cold weather. It is also best to delay watering and fertilizing until spring. Resist watering until new growth appears, and avoid fertilizing until you know the full extent of the damage and have pruned the dead parts. The pruned tree, being smaller, will not need as much fertilizer as before. For now, just kick back and wait until spring or even summer.
Wait to prune until trees show signs of new growth. Identify the branches damaged by frost. Branches that aren’t generating new leaves need to be removed. In some cases, the bark will have a different color than the rest of the tree, or even begin to fall away.
Make all pruning cuts into living wood. Clean pruning tools in a mixture of 10 percent bleach and 90 percent water to prevent spreading disease between trees. If you are pruning more than one citrus tree, clean the tools in between.
Wait to water until the soil has dried out and there is new leaf growth. With fewer leaves to evaporate the water, damaged trees are less thirsty.
When new growth appears in spring, begin fertilizing. Several light feedings are better than one heavy application. Choose a fertilizer formulated specifically for citrus trees. These products are high in the nitrogen and chelated iron that citrus trees need.Apply a two-inch-thick layer of mulch around each tree, extending the mulch beyond the drip line but keeping it at least six inches away from the trunk.
Spring begins on March 20, so I will have to ignore my freeze-damaged trees for a few months before I can pick up my pruning shears and get rid of the unsightly leaves, twigs and branches. Fortunately, now is the time to start seeds for late-spring planting so I won’t be without something to do.
Workshop: Join Napa County Master Gardeners for a workshop on “Rose Pruning” on Saturday, January 18, from 10 a.m. to noon, at the University of California Cooperative Extension (address below). January is the best time to prune your roses. Come learn pruning techniques from a certified Rosarian. Bring your rose questions. Online registration (credit card only)
Mail-in registration (cash or check only).
Napa County Master Gardeners welcome the public to visit their demonstration garden at Connolly Ranch on Thursdays, from 11:00 a.m. until 1 p.m., except the last Thursday of the month. Connolly Ranch is at 3141 Browns Valley Road at Thompson Avenue in Napa. Enter on Thompson Avenue.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.