Native plants can be harmed by unexpected cold weather, including large amounts of snowfall, just like their exotic counterparts. In a completely natural setting this would rarely occur, since these species are adapted to the variable temperature range. However, in the built environment, frost damage is increasingly likely since we frequently use native plants from other regions. Gardeners should look first to their locally native plants as much as possible, since they have evolved to suit local conditions. Plants that originated in Southern California, the Channel Islands or in our low deserts look lovely in gardens, and when winter comes, they may be at the edge of their cold-tolerance range.
Winter brings multiple harsh conditions: precipitation in a variety of forms, wind, and prolonged temperature drops. Plants, when give extremes, usually stop growing, although some native may continue to put out roots if the soil is only moderately cool. Plants are not the only things that can be affected – an unexpected side bonus is that some soil pathogens and insect life can be killed by frost. Even the gophers head for hibernation.
If your nearby native plant nursery is focused on local endemics, they probably won’t have frost-tender plants for sale, but more generalized native plant nurseries, and the exotic nurseries that sell natives as a specialty area, may do so. Most plants should be fine as long as that species is frost hardy, but you may fall in love with something you have see and can’t resist. So, try our suggestions and see what happens. If they make it through the first two winters, they may be strong enough to last their natural span.
Snow is different from plain old cold weather. In fact, snow can act as an insulator since it is fluffy and stays just at freezing. Frost damage occurs when clear skies and no wind exist for extended periods and the natural insulation of cloud cover is exhausted, or when a cold front moves in.
If you are buying new plants, bring them home and keep them in containers in a protected area. Fragile roots are more exposed in planting pots than in the ground. Mound mulch around them, pile up sticks and branches, or wrap them in burlap. Move them temporarily under a porch or on a sunny south side that gets good daylight heat reflected off a wall. Make sure you are planning on planting them when the night temperatures are consistently above freezing. Water them on your regular schedule and during mid-day after a hard frost, until planted.
But what about new fall plantings?
Plants that may also need help include plantings that are frost-hardy, but you just installed them this past fall.
First, make sure you planted in the correct spot. Frost-sensitive plants will enjoy a sunny southern exposure. Rock walls can offer protection, temporary barriers can add seasonal help. Make sure you know your wind patterns in each micro-climate.
An old gardening adage is, “Dry soil freezes sooner than wet soil, and bare ground sooner than covered soil.” Any newly installed area must be mulched as soon as possible after planting. Mulch can help maintain soil temperature and increase a plant’s odds of winter survival. Mulch all new plantings with at least four inches of organic material.
You can cover them with frost-protection fabric, but since these products are usually petroleum-based, an environmentally oriented gardener would avoid these products in favor of solutions that are renewable and recyclable.
Water plants judiciously – balancing the desiccating effects of frost and the variable temperatures predicted with the need to avoid watering just before an overnight freeze. Watering around the root zone of the new planting can raise the soil temperature.
Many plants survive as long as their roots and crown stay healthy. The plant may lose its looks during winter, but will bounce back in spring.
One of our CNPS members from the Cupertino area said, “…in MY garden, anything that couldn’t survive frost has long since died. I feel kind of smug to see the bright green leaves of my mountain mahogany and other evergreen CA native plants like Aster chiloensis, while my neighbor has to tarp his plants if frost is expected. (I’ve not been able to get him to switch to natives, but in his defense, he grows and shares tasty non-native fruits and veggies like strawberries, and we BOTH grow blueberries and raspberries which NEED a frosty winter.)”
Some popular garden natives that have good cold-resistance include coffeeberry (Rhamnus californica), some of the wild currants (like Ribes aureum gracillimum), toyons (Heteromeles arbutifolia), manzanita (Arctostaphylos manzanita), oaks (Quercus kelloggii), sugar bush (Rhus ovata), monkey-flowers (Mimulus subsp.), sages (Salvia subsp.) and wild lilac (Ceanothus subsp.). Look for hybrids that have “mountain” sounding names as a good clue to what the conditions might be for this plant to flourish. Some examples would be Narrow Leaf Cottonwood (Populus angustifolia Mammoth), Shasta Buckwheat (Eriogonum umbellatum polyanthum Shasta), Parry Manzanita (Arctostaphylos parryana Snow Lodge) or Mountain Mahogany (Cercocarpus betuloides).
Protecting existing plants
There are a couple of strategies for protecting plants: proactively protect the most damage-prone plants early in the season, or deal with damage if and when it occurs.
If you want to get a jump on the potential problems, you might want to explore burlap coverings. Gardeners have, throughout the ages, relied on these fabric coverings for tender plants. Martha Stewart has made an artistic statement in her gardens by tailoring burlap covers to perfectly fit her symmetrical and formalized shrubs. You can find other examples at Pinterest.com by searching on the term “burlap winter garden.”
Another alternative is to use cloches of some sort. These are clear bells – most are plastic. But you can still find relatively inexpensive glass products, or even more pricy – look for Antique French cloches. An example is shown at this British web site – Haxnicks.
Potted plants may need protection, too. The French cloche is a good solution, as may a recycled plastic gallon jug. Since Californians use their garden so much of the year, do look for attractive and ecologically sound alternatives.
Treating frost damage
The first sign of frost damage may be drooping tips that look as if they wilted. If above-ground parts of your plant freeze, don’t prune this material off right after the frost. Wait until all frost danger has passed for the season. The dead material provides insulation and is the plant’s way of protecting the crown. Prune too early and you may cut back too much. Or, worse, there may be another frost and you will have exposed your garden to a more radical freeze on tender, newly exposed plant material.
Here are some resources that will allow you to explore this topic further:
Do you know of any more resources? Have you got some experiences to share? Please leave links in the comments section, and then I will update this information.