Cold Hardiness of Five Eucalypts in Northern California

Thirty years ago, I began planting eucalypts in my garden in Concord, California, located about thirty miles inland from San Francisco (in Sunset zone 15). California’s mediterranean climate is ideal climate for temperate and near sub-tropical gardening. Rainfall is usually confined to the winter months, and, in most years, frosty nights are sporadic and rarely cause any major damage.

The problem in growing most eucalypts in Northern California is that, unlike Australia, the San Francisco Bay Area does experience, every ten years or so, a severe freeze when nighttime temperatures drop into the low 20s F (‑4° to ‑6° C). Temperatures this low can destroy many Eucalyptus species. If they are not killed outright, they will be reduced to stumps and the new growth will resprout along major branches, along the trunk, or from below ground level. This behavior, generally, is not acceptable to most gardeners, who expect mature trees to remain, at least, the same size year after year.

Of the many eucalypts in my garden, five are of particular interest because of their beautiful foliage and flowers: Eucalyptus erythrocorys, E. macrocarpa, E. grossa, E. gillii, and E. citriodora. None of ...