The last several nights have threatened frost, even down here in the mid-lowlands of my garden in the southern section of Pasadena. While the end of January is the average last frost date for our area, I haven’t worried much about it for quite a few years since we haven’t had even a light frost in more than a decade. But the possibility is always there at this time of year, especially for more highland gardens than mine. So, here are some thoughts to help you understand the possibility/probability in your locale.
Why Frost Happens
Frost—or indeed any “bad” thing—actually happening in our gardens is the result of several factors that I’ve adapted from the Plant Pathology “Disease Triangle.”
—Pathogen—the “disease”—or “pest” or “frost” mechanism. While diseases and pests are pretty much always around in our gardens during their particular life cycles, frost conditions exist only during our winters. But whether or not they result in damage in your garden depends on the other two factors.
—Environmental Conditions. For pests, this means the temperature, humidity and other elements that they consider close to ideal and so they may thrive. For frost, this means not only being close to 32 degrees Fahrenheit freezing temperatures but also whether the soil is hydrated (our rains confirmed that), the wind is blowing (lowering the freeze factor or keeping the frost from settling), where the plant is located (next to a wall or out in the open), etc.
—Host Plant Susceptibility. Is the plant more likely to attract the pest or be damaged by frost?If the plant is healthy and of a resistant variety, it’s less susceptible to a particular pest; if it’s worn out from a season’s growth or not resistant to that pest, it’s more susceptible. Regarding frost, if it’s a tender begonia, it is definitely more open to frost damage; but if it’s a deciduous plum tree that’s already dormant, frost is less of a potential problem.
All three of these conditions must be met for the pest or the frost to affect the plant. If any of the three isn’t existent, then chances are there’ll be no damage. Also, time is a limiting factor – long enough for all the conducive conditions to be in effect for the pest or frost to actually inflict damage.
How to Protect Against Future Frosts
You can change a couple of the environmental conditions to preclude frost damage. First, recognize that frost falls straight down on still nights.
—Move container plants under eaves so they’re shielded by the roof above.
—Provide top covering for plants in the open. For example, if you’re still nurturing old tomato plants for those last few slowly-ripening (or at least coloring-up) fruits, provide cover above the plant that extends out just beyond the foliage. Unless you also get freezing winds, no need to wrap the plant entirely; the top protection is most critical.
—A caveat regarding using plastic, however—don’t let it touch the plant leaves, since this will literally transmit the chill damage directly where it touches. Let there be some open air to act as insulation between the plastic and the plant foliage.
—Keep plants hydrated. With all of our wonderful rains so far, plants may be fine for at least a couple more weeks before needing irrigation or more rain.
If Some of Your Plants Have Already Been Nipped
You may not know for several days whether a plant has been damaged by frost, since the foliage may not go limp and shrivel for a while.
When you do see damage, it’s best to not trim it off immediately, even though this may offend your sense of aesthetics and desire to keep plants neatly trimmed. The dead foliage will serve as protective interference for the tender interior of the plant from further damage from later frosts.
Although it may take a month or so for new growth to appear, it will define precisely how far the dieback actually occurred on each branch—sometimes considerably less than you would have guessed when first observing wilted leaves.
For more advice and insight from Yvonne Savio, please visit GardeningInLA.net (and find more winter garden images and suggestions below events listing.
Yvonne Savio grew up and still lives on a 3/4-acre hillside city lot in Pasadena, growing fruits, vegetables, and flowers year-round in manure- and compost-amended gardens. From years of gardening, she knows what “harvested at the perfect moment of ripeness” means and is passionate about enabling others to enjoy the benefits of “growing your own.”
Yvonne earned degrees in journalism, English literature, art and photography from California State University at Los Angeles and Sacramento; her horticulture degree is from American River College, Sacramento. For 15 years, she worked in the Botany and Vegetable Crops Cooperative Extension Departments at the University of California, Davis, where she conferred with Statewide Vegetable Specialists regarding cultural and postharvest handling techniques. In the early 1980s she helped initiate and develop the Master Gardener Program in Yolo County. From 1994-2015, she managed the Los Angeles County Master Gardener Program, teaching 1,183 volunteers who then helped 1.3 million residents to garden more sustainably.
Yvonne maintains demonstration and trial gardens in Southern and Northern California, specializing in drought-tolerant techniques for growing vegetables, fruits, perennials, roses, and succulents. She documents the creative fun stuff of repurposed tools and garden art. She loves chatting with gardening groups; for more of her presentation topics. see GardeningInLA.net/speaking.
Yvonne shares upcoming events:
|Hardy Geraniums for Southern California
Thu, Feb 9, 2017 from 7:00pm – 9:00pm @ Friendship Auditorium
|Southern California Horticultural Society monthly meeting. Non-members welcome; $5 admission. Robin Parer will discuss geraniums, with a plant raffle and sale of her book.
We are please…
|California Native Plant Horticulture
Sat, Feb 11, 2017 from 8:30am – 12:30pm @ Theodore Payne Foundation for Wild Flowers and Native Plants
|The basics on gardening with California flora: why natives are valuable, about plant communities, plus planting techniques, establishment, irrigation, pruning and ongoing maintenance. Recommended fo…|
|Propagating California Native Plants
Sat, Feb 11, 2017 from 9:00am – 12:00pm @ Theodore Payne Foundation for Wild Flowers and Native Plants
|Learn basic skills of vegetative propagation with TPF’s Propagation Manager! Various species of native plants will be discussed and started from cuttings or divisions in this hands-on session, a…|
|UCLA Extension Horticulture & Gardening Information Session (must RSVP beforehand)
Sat, Feb 11, 2017 from 9:00am – 10:30am @ UCLA Extension, Gayley Center (Westwood Village)
|Interested in taking your passion and turning it into a career? The UCLA Extension Horticulture & Gardening certificate program can prepare you with the knowledge and skills you need to become a p…|
|Orange County Coastkeeper Monthly Garden Share
Sat, Feb 11, 2017 from 9:30am – 10:30am @ Coastkeeper Garden
|Love to garden but hate paying high prices for new plants? Want to try out some new types of plants for your garden? One of the best kept secrets in Orange County is the Coastkeeper Garden Share! Jo…|
|Seed Workshop for Kids (ages 6-11)
Sat, Feb 11, 2017 from 2:00pm – 3:00pm @ Theodore Payne Foundation for Wild Flowers and Native Plants
|A fun, hands-on session for budding gardeners and kids with an interest in what seeds are and how they grow. Each child will leave with two 4-inch pots of freshly sown seed for their garden and a pack…|
|Sketching and Plant ID (must preregister)
Sun, Feb 12, 2017 from 9:00am – 4:00pm @ Various locations in Los Angeles
|Held at locations in and around the Southern California area, this course is an introduction to scientific illustration and plant identification. Students are introduced to plant taxonomy and terminol…|
|One Hour Workshops
Sun, Feb 12, 2017 from 10:00am – 11:00am @ Fountain Community Gardens
|Master Gardener Dan Fujiwara will present a new gardening workshop every Sunday through February 26, 2017….|
More pictures from Yvonne’s garden this winter…