- Author: Laura Elisa Garza Diaz
Frost Protection Regulation - Laura Garza (1)
Winter has finally arrived in the north state! Winter temperatures can pose a threat to the fruit and foliage of citrus, as well as other succulents, tender perennials, tropical and subtropical plants.
The most common type of frost in California is referred to as radiation frost. Radiation frost occurs on cold nights when the air is clear and still. Soil, buildings, plants, and other objects at the earth's surface act as a heat reservoir by absorbing heat during the day. Heat is lost, or radiated, from the earth's surface into the atmosphere and plants are damaged when enough heat is lost from this reservoir to lower the temperature at the surface to below critical temperatures. Greater damage occurs with colder temperatures or a longer duration of cold. Temperatures can drop more rapidly when the air is very dry and the dewpoint is low. If the dewpoint is very low a freeze can occur without the formation of dew and frost. This condition is known as a “black frost.”.
Avoid planting frost-sensitive trees in the lowest areas of the yard or garden, as cold air tends to flow downhill and can accumulate in such depressions. Trees planted near structures or walls, particularly those with southwest exposure that absorb and retain reflected heat during the day, may be damaged less during periods of frost because that heat is released during the night. Fertilize and prune during the spring and early summer so that new foliage will have enough time to mature before the onset of cold weather. Bare, moist soil stores more heat during the day and radiates more heat during the night, so rake away mulch, ground cover, weeds and leaves from around the tree during cold weather.
Monitor weather forecasts and take note of how low temperatures will go, and for how long. When the weatherman warns of frost, there are several precautions you can take to protect your plants.
- Identify cold spots in your landscape by monitoring with thermometers
- Identify plants at risk: citrus, succulents, tender perennials, tropical & subtropical plants
- Have supplies ready: either sheets or blankets with stakes or a framework to hold covers off foliage, or frost cloth (which can lie directly on plant foliage); lights; wraps for trunks; thermometers.
- Wrap trunks of tender trees, using towels, blankets, rags or pipe insulation.
- Move potted plants to warmer spots next to the house or under a patio cover.
- Water plants and trees. Dry plants are more susceptible to damage and moist soil retains heat better than dry soil.
- Cover plants just before sunset to capture and hold in as much heat as possible. Remove sheets/blankets daily if it's sunny, to allow soil to absorb heat during the day.
- Add heat by hanging a 100-watt lamp designed for outdoors in the interior of the tree, or use a holiday string of outdoor lights (not LED lights, since they don't give off heat).
If the larger branches of a tree or plant sustain frost damage, don't prune away damaged wood or remove the plant too soon. Wait several months in order to assess the extent of the damage and allow time for possible recovery during warm weather. As new foliage begins to grow, frost-killed twigs and branches will be apparent and can be pruned at that time. Postpone heavy pruning until the following year to allow trees to regrow to the point where damaged wood can be clearly determined.
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at 530-552-5812. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.
By Penny Pawl, UC Master Gardener of Napa County
I was recently at the garden of one of my fellow Napa County Master Gardeners, Cindy Watter, and was amazed by her wonderful Brugmansias (Solanaceae) and their huge blooms.
Cindy has had these plants for several years and they continue to give her and her garden guests a wonderful floral display. Some are planted in large pots and others are in the ground.
Brugmansias are sometimes called Angel Trumpets for the large dangling flowers they produce. These flowers are scented and attract pollinating moths. One species is pollinated by hummingbirds that are able to reach deep into the hanging flowers
Cindy had given me some cuttings from her plants, and I was able to root them over the winter in my hothouse in a soil mixture created for that purpose. As winter nears, Cindy cuts her Brugmansia back to one to two feet tall. She also covers them with a fabric that protects them from cold winter nights.
We live only about 10 miles apart but in vastly different microclimates. She is in the middle of Old Town Napa and big trees grow around her garden. I live beside and behind open vineyard areas and frost can be fierce, damaging tropical plants. Brugmansia are native to Central and South America and will not survive frosts.
Napa has many microclimates. Conditions at a 200-foot elevation are different than on the valley floor.
Brugmansia no longer grow in their native areas, but because of their popularity, they have been introduced to many other areas. Some people theorize that the plants no longer grow in their native areas because the animal that spreads their seed is no longer in the area.
Brugmansia bloom in a variety of colors including white, yellow, pink, orange, green, and red. Most of these plants are hybrids, bred for various flower colors and other traits. When a test plant produces a bloom in the desired color, it is reproduced by cuttings to ensure its offspring have the same traits and flower colors. Plants grown from open-pollinated seeds often revert to their native types.
I was surprised to learn that Brugmansia are in the Nightshade family, which includes potatoes, eggplants, peppers, and tomatoes. Brugmansia are poisonous and should only be admired, not tasted. However, a tropical butterfly (Placidula euryanassa) feeds on the nectar, which makes the butterflies and their larvae taste bad to predators.
While Brugmansia are related to Datura, there are differences. Plant botanists have been debating and reclassifying these plants since the mid-1700s. Datura flowers turn up and Brugmansia blooms dangle.
Brugmansia are heavy feeders. Cindy uses a balanced fertilizer about every three weeks on the potten plants to keep them healthy and growing. Because they are native to the tropics, they also like to be kept damp. If they are stressed for water, the leaves will wilt. Plants growing in the ground don't need to be watered as often.
Planted in the garden, Brugmansia can reach 15 feet in height, but most stay under that. The flowers usually appear only on new wood above a certain height. Old wood cuttings don't flower until they have forked and reach that height. The leaves are the same size as the flowers.
Brugmansia grown in pots need to be occasionally moved to a larger container or be root-pruned while dormant, and replanted. They do well in dappled shade.
Food Growing Forum: Join Napa County Master Gardeners on Sunday, July 26, from 3 p.m. to 4 p.m., for a free Zoom forum on “Watering, Irrigation and More.” This forum on food growing will continue monthly on the last Sunday of every month, with future topics announced soon. To receive the Zoom link for the July 26 forum, register at http://ucanr.edu/FoodGrowingForum2020.
The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening, upcoming events or to submit gardening questions, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed to walk-in questions, but we are answering questions remotely and by phone or email. Submit your gardening questions through our website, by email mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143. Master Gardeners will get back to you within a few days.
by Denise Seghesio Levine, U.C. Master Gardener of Napa County
In other parts of the country, people focus on inside tasks in November. Garden tools are already oiled and hung for the winter; bulbs are dug and cellared. Treasured perennials, pots of citrus and fragrant herbs have been brought inside to wait out the winter in bright, warm rooms. With the exception of raking the last leaves or shoveling snow, gardening chores in these locales are largely complete for the next few months.
A few years ago, while visiting the Department of Energy's National Laboratories in Idaho, I lunched with one of the engineers. It was October, and the quaking aspens were aflutter with glorious chartreuse- and lemon-colored leaves. The skies were a true cerulean blue and I could not imagine a prettier or more wonderful time to be there.
My host had a different view. His favorite time of year was coming, when the skies turned gray and black and the white, quiet snowflakes came down. Each year, snow buried not only his garden, but also his tool shed where he housed his lawnmowers, leaf blowers, shovels, loppers and other garden tools.
The only survivor was the family's snowmobile fleet. Until spring thaws uncovered the first flecks of green, he had a vacation from garden chores. Snowmobiling with the kids during the day, hot chocolate and puzzles at night—no wonder it was his favorite time.
Here in Napa Valley, November brings is no rest for the garden weary. The list of potential planting opportunities and chores can be just as encompassing and just as long as in spring and summer.
November in Napa Valley is one of the best times to transplant. If you have plants that have outgrown their pots on the patio or their boundaries in the garden, or are underperforming in their current spot, now is the time to rehome them.
If you use a copper spray for peach-leaf curl, the first application is usually around Thanksgiving. Start watching for frost now and be ready to toss a cover over your citrus and other frost-sensitive plants.
If you want to add plants to your garden, stroll the nursery aisles and look for new discoveries. Read the labels to make sure you are choosing a plant that will thrive in your garden. Some plants are dormant now; others appreciate being transplanted when they will have months of moisture to sink roots deep before the stress of summer.
Local nurseries have beautiful bulbs to plant now for spring bloom and annuals like pansies and violas for winter color.
Tender green crops like lettuce, spinach, orach, arugulas, mint and cilantro all do much better in the cooler months. Plant seedlings or direct-sow seeds in small amounts every couple of weeks for a steady supply into spring. Arugula can be sown liberally in the corners of your garden where it can spread. Better a “weed” I can pick for salads than an inedible weed.
Peas, both pole and bush varieties, can be planted now, as can sweet peas. Wildflowers and many annuals can also be sown now and will germinate when the weather warms in spring.
Keep your flowering sweet peas and edible peas apart. While munching sugar snap peas and petits pois right in the garden is a delight, all of the ornamental sweet pea flowers and pods are toxic. Remind your young children: ornamental sweet peas are eye and nose candy only.
Garden and salad crops like each other, so it is easy to get the most out of a small winter garden patch. Green scallions do well when planted alongside lettuce and carrots. Pole peas enjoy a frilly bed of lettuce along the base, and I have never seen a radish that did not like being near lettuce. Always check seed packets to make sure the variety you have in your hand this month does well from fall to winter.
Your favorite nursery will have vegetable and flower seedlings for planting in November. Expect to find a variety of onion sets and seeds, broccoli seedlings, kohlrabi, rutabaga and perennial herbs.
Seeds can be planted directly outside this month as well. Read the seed packets and look for lettuces that thrive in the cold months. Other good options for winter include spinach, chard, Asian greens, mesclun, sorrel, miner's lettuce and cabbages.
If you have hopes of blooming amaryllis for Christmas, this is the month to pot up heavy, blemish-free bulbs. They will burst into bloom in time for the holidays. Follow the directions that come with your bulbs, and maybe by Christmas we can take some time off.
Library talk: Napa County Master Gardeners will give a talk on “Beyond Peaches and Apples: Unusual Fruits for your Backyard” on Thursday, November 7, at 7 p.m. at the Napa Library, 580 Coombs Street, Napa. Attendance is free.
Next workshop: “Holiday Décor Gifts with Succulent Plants” on Saturday, November 16, from 9:30 a.m. to 12:30 p.m., at the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. For more details & online registration, visit http://napamg.ucanr.eduor call 707-253-4221.
The UC Master Gardeners of Napa County are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.
- Author: UC Delivers
Reprint of UC Delivers article
The Issue
What Has ANR Done?
Research at UC Berkeley's College of Natural Resources has shown that frost-sensitive plants are damaged only when ice forms in the plant, not by cold temperatures alone. Further, certain common plant bacteria trigger ice formation by a process called ice nucleation. In the absence of these bacteria, plants do not freeze until faced with relatively cold temperatures. By inoculating crops early in their seasonal development, research has shown that ice-nucleation active bacteria can be prevented from growing. In the field, researchers demonstrated that both the altered bacteria and naturally occurring bacteria successfully competed with the ice-nucleation active bacteria on the potato plant. This represented the first field use of genetically engineered microbes in the world. Both reduced the freezing temperature of crops from 2 to 6 degrees F and reduced plant frost damage during typical frosts of about 28 degrees F by an average of 80 percent.
The Payoff
Frost damage reduced by up to 80%
using bacterial spray derived from research
A naturally occurring bacterial strain from a pear tree in Healdsburg was found to improve control of frost damage when sprayed onto crops. This bacterium also controls fire blight, a devastating disease of pear and apple trees. The bacterium has been commercialized as a freeze-dried preparation of live bacteria that can be sprayed onto crops with standard agricultural spray equipment. This product, Blightban A506, can provide considerable control of frost damage and is registered by the U.S. Environmental Protection Agency for use on a wide variety of crop plants, including pear, apple, strawberry, peach and potato. In the western U.S. and other regions, approximately 50 percent of the crop acreage, such as pear and apple, is treated with this antagonistic bacterium for both frost and disease control. The use of this biological control agent provides an environmentally safe and economical means of frost protection, ensuring crop productivity even when cold temperatures strike.
Learn More
Blightban A506 is registered for use on a variety of crops. It is produced by Nufarm Americas. They may not have much in the way of technical materials. "If any of your growers would like to give this a try I would be glad to answer any questions" Steven Lindow. Contact information below.
Peer Reviewed
The Role of Bacterial Ice Nucleation in Frost Injury to Plants, Steven E. Lindow, Deane C. Arny, and Christen D. Upper, US National Library of Medicine, Plant Physiology.
Interactions of Antibiotics with Pseudomonas fluorescens Strain A506 in the Control of Fire Blight and Frost Injury to Pear, Steven E. Lindow, Glenn McGourty, Rachel Elkins. The American Phytopathological Society.
Contact
Steven Lindow, UC Berkeley Department of Plant and Microbial Biology
(510) 642-4174, icelab@berkeley.edu
ice nucleation ann rev