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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Dec 31

Winter Cold

Posted on December 31, 2015 at 10:05 AM by Ann Vallee

by Charlene Burgi

The temperatures plummet as we sleep the night away. The slight breeze wafting in from the north creates an illusion of subfreezing air currents, despite the 38 degrees flashing on the digital signage at the local banks in town. As we hunker down under electric or down blankets, our plants must face the cold.

Some plants are unable to withstand cold weather. Tropicals, annuals, and some perennials do not have the ability to prevent ice crystals from forming inside their cell walls as temperatures drop. Other plants can ward off the ice crystals, but suffer from freezing in the intercellular spaces—this is what my daphne experienced the first year I moved to Lassen. The leaves appeared dried out or burned, but fortunately the plant survived and grew new leaves in the spring.

Cold tolerant plant - manzanita
 Cold-tolerant manzanita
Other plants have a built-in system that produces—in simple terms—an anti-freeze substance that protects the cells of the plant. This sucrose/protein substance is not something we can purchase at our local nursery. However, there is a product on the market called Cloud Cover that can help limit transpiration and protect plants in cold weather. Apply several hours before the temperatures drop to help prevent borderline varieties such as citrus from freezing.

When we know temperatures are going to drop, it is best to water container plants as the moist soil will retain some heat and protect the root system. Move them under an eave or covered porch.

Plants in the ground will require a different treatment. Create tents with burlap or sheets and place an oven or refrigerator light bulb under the sheet. If using an extension cord, be certain to wrap all connections well with electrical tape. Be careful to keep sheeting material away from the leaves.

There are some other decisions to consider before we get into the depths of winter-chill. First, mulch, mulch, mulch to protect the roots of plants. Do not prune back perennials such as lavender or sage. Their leaves act as a blanket and can be cut back after the last frost days in spring.

The aforementioned tropical plants provide such beauty that they are difficult to resist when we see them in bloom. Marin's planting zone puts these tropical plants on the fringe of growing here, so the temptation is great for bringing them home. If this is your story, give these plants a chance by installing them on the south side of the house where reflected heat will help sustain them during cold weather.

Frostbitten rose leaves
 Frostbitten rose leaves
Despite our efforts to protect our plants, frost damage may occur. If you see damaged leaves or dried stems, do not prune the damage until the danger of frost has passed. Then, with small pruning cuts, snip back the damaged plant until signs of green wood appear. I can always count on new growth from the roots of the bougainvillea growing at my home in Novato.

Bundle up and have a very happy new year.

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