Winter Hardiness

Survival Strategies

As winter approaches each year, we make many preparations for the cold like adding antifreeze to our cars and changing the filter on the heater, to help prevent damage to mechanical things. Plants also need to prepare for the oncoming cold and they do it in a variety of ways.

‘Hardiness’ refers to a plant’s ability to withstand cold. Some species of plants are more resistant to cold temperatures than others and, therefore, are hardier.

You can further divide cold hardiness into shoot, flower or root hardiness. Many fruit tree blossoms are damaged by a cold spell although the tree itself is not damaged.

In the fall, cold-sensitive plants go through a transition known as “hardening off” when they shift from a tender state to a hardy state of dormancy by dropping their leaves and concentrating their carbohydrates within the cells to help protect the tree or shrub from cold injury.

It is important when choosing plants for the landscape to pick ones that are hardy in your climate zone. The USDA has established a map of 11 zones based on average low temperatures for each region. In Willits we fall into Zone 8B with low temperatures between 15° and 20°F. But there are “micro-climates” throughout the area that experience warmer or colder temperatures during any given cold spell.

The USDA zones only address low temperatures. Such factors as precipitation, soil type, wind patterns and humidity are not considered. An alternate guide that does address these factors is the Sunset Garden Book, but that also is not perfect. It places Willits in Zone 14, the same as Ukiah, Cloverdale and San Jose. Our experience has shown that plants that will grow in Sunset zone 7 as well as zone 14, are better adapted to our colder winters.

If you have chosen plants that are hardy enough for your area, the best advice for preparing your plants for the cold is to do nothing. For example, don’t prune. Pruning can stimulate stem growth or at least cell growth for healing wounds. Don’t fertilize since fertilizer also can stimulate growth. Let plants alone so that they can slow down and toughen up for the wintry months ahead.

Placing a layer of mulch down around the bases of your trees and shrubs can help reduce temperature fluctuations and moisture loss. Shape the mulch like a donut not a volcano, leaving a space between the mulch and the trunk of the tree to discourage rodent damage.

Finally, keep your eye on the water. Plants don’t need as much water when they are dormant, but a cold, dry spell can spell disaster especially for evergreen plants. Don’t forget plants in containers, which may miss out on the rainfall. They need to stay damp throughout the winter.

    • Compost your leaves, don’t burn them! Leaves make wonderful compost that breaks down into rich humus by next summer, while burning pollutes the clean fall air and contributes to breathing problems of friends and neighbors.
    • Liquidambar trees can’t be beat for fall color. Choose them now while you can see their bright colors.
    • Clean up dead foliage on perennials like peonies, daylilies and balloon flower and cut back dead flower stems on Echinacea, blanket flower and penstemon.
    • ‘Tete a Tete’ Narcissus are the cute little yellow daffodils that are popular in pots. Plant some now for fragrant blooms next spring.
    • Plant bright red amaryllis in pots now for Christmas gifts.

One Response to “Winter Hardiness”

Leave a Reply

You must be logged in to post a comment.