Cold Hardiness of Olive Trees02/09/2015
The cold hardiness of olive trees is greatly exaggerated on some websites. Claims that olive trees can withstand 5 degrees Fahrenheit is true only inasmuch as shoots MAY re-emerge from the root crown several months after the entire top and most of the trunk have been killed. In this case, it will take several years to have a producing tree again and even a moderately hard freeze in the intervening years can be devastating.
Serious cold damage to olive tree branches begins at 22 degrees, though lesser damage to fast-growing branch tips can occur at 27 degrees if frost is present. Temperatures of long duration in the mid-teens can cause very serious damage to larger branches and trunks, and the extent of the damage may not be evident for some time. Damage from cold is exacerbated when the temperature swings sharply from very warm to very cold conditions over a short period of time, as occurs during cold fronts in north and central Florida.
Duration of cold is an important factor. If the temperature falls to the low twenties early in the evening and persists until late morning, damage will be much greater than if the same low temperature occurs for only and hour or two.
Within a particular USDA Cold Hardiness Zone, low temperatures can vary somewhat due to variations in topography, moisture content of surrounding soil and the presence of "heat islands" created by cities and other large infrastructure. In general, however, we at Olive Tree Growers cannot concur with claims that olive trees can thrive in USDA zones 7b or lower and 8a can be questionable, depending upon the particular winter and the particular location.
Many people do grow olive trees in locations generally considered too cold for them and take extreme measures to protect their trees during times of low temperatures. At Olive Tree Growers, we offer our trees only in areas where they can be reliably grown outdoors; anyone who elects to plant olive trees in colder climates should have a well-considered winter-protection strategy ready for implementation.