Cold-Resistant Avocado Trees
Avocados grown here originated in either Guatemala or Mexico. Although larger and often boasting richer flavor, Guatemalan types (Persea americana guatemalensis) suffer more in frosts and are recommended only for U.S. Department of Agriculture plant hardiness zone 10. Mexican types (P. a. drymifolia), on the other hand, show more resistance to the cold and can be successfully grown in USDA zones 9 and 10. "Hass" and "Fuerte," two of the most popular varieties, have been hybridized and share traits of both types.
Frost Resistance of Varieties
In general, Mexican avocados can survive lower temperatures than the Guatemalan. "Mexicola," particularly, exhibits rapid recovery from a freeze. It does not defoliate until the temperature drops to 20 degrees Fahrenheit for four hours; the trunk will be killed at 17 degrees F. "Duke" is another outstanding Mexican performer, hardy to 22 degrees F. "Ganter" and "Topa Topa," both with Mexican ancestry, can withstand four hours at 23 degrees F. The hardiest of the hybrids, "Bacon," recovers from freezes to 25 degrees F, followed by "Hass" and "Fuerte," capable of taking 26 degrees F. The most cold-tolerant of the Guatemalan varieties, "Queen," is also hardy to 26 degrees F. Home gardeners often find more success growing avocados in the cold than commercial growers, because backyards tend to hold more heat than open fields.
Avocado Frost Protection
After choosing the variety, determining where to plant an avocado tree should be the next step toward protection from frost. Planting above a slope or near the house may afford the most warmth. Since trees have more vulnerability in their youth, spread rugs or blankets on structures above the young trees when a frost is predicted. Install lights to burn through the night, or wrap trunks with sponge foam for further protection. Running water through a hose on the ground or a sprinkler system can also supply heat to the trees.
Damages From a Freeze
During periods of freezing temperatures, avocado leaves may appear wilted. Actually, this is a protective response by the plant and does not indicate that the leaves have frozen. Leaves become stiff, brittle and sometimes curled when frozen. Foliage injury can be recognized immediately, but the full extent of damage may not be apparent for months. If the branches and trunk are not greatly damaged, the leaves will shed quickly. This leaf-shedding is an encouraging sign that the tree will survive. Discoloration, splitting or loosening of the bark often means that the tree has been fatally damaged. Do not prune the tree or even attempt to assess damage until time for the new growth in spring.
Rehabilitating Freeze-Damaged Avocados
Sunburn of the twigs and branches exposed after defoliation threatens the freeze-damaged trees, even if temperatures stay relatively low. Whitewashing can prevent it and should be the only treatment done immediately after a freeze. Dilute a white latex paint with water, and spray all exposed tree parts. Be careful not to thin the paint too much, as the whitewash needs to be truly white when it dries on the tree to offer the necessary protection. While your avocado tree recovers, go lightly on feeding, watering and pruning, or you may overwhelm it and cause further damage.
- The New Sunset Western Garden Book; Kathleen Norris Brenzel
- California Rare Fruit Growers: Avocado Fruit Facts
- University of California Agriculture and Natural Resources: Avocado
- University of California Agriculture and Natural Rexources: Avocado Production in Home Gardens
Mary Simpson began her writing career in 1968 on a Dallas oil magazine. Besides reporting and editing for several small Texas newspapers, Simpson has written for "Petroleum Engineer Magazine," "Denton Today Magazine" and put out an employee newsletter for a FEMA facility. She holds a B.A. in journalism and an M.A.in English, both from the University of North Texas.