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.
Dahlias!
In my opinion, there is no more striking addition to a garden than dahlias. With their vibrantly colored, large blooms and curled petals, they demand attention.
I have had dahlias before, but this is my first year growing them from tubers. They come in almost any color you could want and in sizes ranging from a few inches across to the diameter of a dinner plate (and actually called “dinner-plate dahlias”). I finally decided on a flashy cultivar with yellow and red stripes called ‘Sunrise Mango.'
What explains such diversity? Dahlias, as it turns out, have a more complex and variable genetic structure than most other flowers, leading to impressive variety. There are 42 different species and at least 57,000 different cultivars. The International Registry of Dahlia Names keeps track of them.
Before horticulturalists began breeding dahlias for ornamental purposes, the plants were grown for food by the Aztecs, who ate the tuberous roots. Today, the roots are still used in Oaxacan cooking, and an extract obtained from them is a common addition to Central American beverages. Don't go chopping up your dahlia tubers just yet, though. The ones you get from your local nursery have been cultivated for appearance, not flavor, and will likely not be to your taste.
The flowering portion of the dahlia is also unusual. Known as a "composite" bloom, it holds not one but many flowers. The multiple small flowers, called florets, are often mistakenly identified as petals. Lacking much fragrance, the plants use these showy blooms to attract pollinators.
When planting dahlias, choose a site with plenty of sun and good soil. Gentle morning sun is best. Warm, well-drained soil is another must. Make sure the planting area is not overly wet (light dampness is okay), and the soil temperature is at least 60°F. Cold, wet soil can cause tubers to rot.
Dig a planting hole four to six inches deep and slightly wider than the tuber. Do not add compost, fertilizer or potting soil containing fertilizer. Instead, sprinkle about a tablespoon of bone meal in the bottom of each planting hole. Thenplace the tuber sideways in the hole with the "eyes" facing up. Stems will grow from these eyes.
Do not water after planting. The natural moisture in the soil will suffice. When the sprouts are four to six inches tall, begin watering deeply once or twice a week.
Young dahlias are frost sensitive, so protect them if frost is predicted. Begin fertilizing when you begin watering, using a fertilizer with more phosphorus and potassium than nitrogen, such as one labeled 5-10-10. Too much nitrogen (the first number listed on the fertilizer package) can cause weak plants with few blooms, or even kill the tuber. Phosphorus and potassium, on the other hand, will help produce strong plants with plentiful flowers. Dahlias generally bloom about eight weeks after planting, or around mid-summer.
Bark is generally a good groundcover for gardens but not around dahlias. Mulching with bark might keep the ground too cool and damp and raise soil acidity, conditions dahlias don't like.
Avoid fungal diseases, common to dahlias, by planting in a location with well-drained soil and plenty of sun. Slugs and snails love dahlias. Handpick them at night when they are most active. If you're not up for a flashlight-enabled search and destroy mission, try placing a small piece of wood or an overturned flower pot in your garden. Snails and slugs will use it as a daytime hiding spot, and you can remove them then.
Aphids, thrips and spider mites can also badger dahlias. When encountering an infestation, I use my garden hose to gently spray off as many as possible. I follow this with an application of Neem oil, a natural treatment for many garden maladies. The oil suffocates pests and fungi but does not harm plants or people. Ladybugs, lacewings and predatory wasps also provide some control and are available at local nurseries. Children love releasing and watching ladybugs.
In Napa Valley, you can leave dahlias in the ground over winter. To give them some extra protection from cold, place a two-inch-thick mound of mulch over each tuber. Remove the mulch in the spring to allow the soil to warm again and encourage sprouting.
Over time dahlia tubers will divide and can become crowded. If you sense that this is happening, gently lift the tubers in fall, about two weeks after a frost. Then store them in paper bags in a cool, dry place until the following spring. Before replanting, divide the tubers, leaving at least one “eye” on each piece.
If you are ready to try your hand at dahlia growing, or just want to know more, please plant to attend the upcoming Master Gardener seminar "All About Dahlias." Details are below.
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.
