There are fruit trees that simply won’t grow here due to our climate. That is an easy fact to acknowledge.
Several decades ago, everyone knew that olives wouldn’t grow in Texas. Today, there are commercial olive groves in the southern part of the state.
And then well-knowing folks said that olives could never grow in eastern Texas. To date, I have it on good authority that there is now an olive grove being grown in southeast Texas. I don’t know how they made it through the cold spell from last winter but I’m anxious to find out.
Let’s be clear from the get-go, olives may certainly be a stretch due to our occasional freezes in a typical winter.
Winter climate is the most important limiting factor in the distribution of the olive in Texas. Temperature controls growth, reproduction, and survival of the olive.
Gradual temperature change is a friend of the olives.
Sudden swings in temperatures in our winter months is a harsh enemy.
The olive that I speak of should not be confused with the Russian-olive (Elaeagnus angustifolia) or the Anacahuita (Cordia boissieri), which is sometimes called the Texas or Mexican Olive. Both of these plants belong to different botanical families. The olive, however, is related to the Desert Olive (Forestiera sp.) and the American Wild-Olive (Osmanthus sp.). The fruits of these other two “olives” are not edible.
Olives begin growth after mean temperatures warm to 70 degrees F in the spring and continues until temperatures drop below this point in the fall.
Unlike the fruit trees that we are familiar with, such as the peach, the olive does not set fruiting buds in the fall. Instead, the olive will only set flower buds after being exposed to cool night (35-50 F) and mildly warm day temperatures (<80 F) during the winter. This unique warm day/cool night weather pattern is called “vernalization” and is essential for fruit bud development with the olive. And olive varieties differ in the range of tolerable temperature that will satisfy this requirement.
No problem yet for our part of the world, right? We can have cooler nights and warmer days.
Olive trees must experience vernalization to produce fruit. Different from chilling hours for most fruit trees and different from the USDA Zone 8b that Lufkin is in for the expected minimum winter temperatures, “vernalization” is a cold period where specific plants not only go dormant but must be exposed to a certain number of days with minimum temperatures or they will not flower.
Think of cold hardiness in olives as similar to citrus, improving with tree age and increased trunk size. It will sustain damage to leaves and small stems at 17º F and more severe damage at 12º F. The tree can be killed to the ground with temperatures below 10º F, but mature trees can re-grow from the underground crown following a severe freeze.
Survival and freeze damage of olives depends on how long the temperature stays low as well as how well the trees are hardened off. Hardening off is a term that describes how plants slowly adapt to cooler, then colder weather. A sudden drop in temperature could from 95 F to 25 F may be enough to kill olive trees.
According to studies conducted over the years, there are very few sites that meet the climactic requirements of the olive in Texas. Studies from Texas A&M University indicated that the olive could be grown as a fruit tree in large parts of East, Central, and South Texas.
Great news, but the same studies determined that the trees would freeze to the ground every three of ten years.
Once established for 3 to 5 years, olive trees gain more cold hardiness, however Texas climatic conditions are very erratic particularly in the middle of the winter. It is not uncommon for warm spells that plummet to freezes. Such events lead to the loss of cold hardiness or acclimation of the olive trees.
So if you are still interested in experimenting with olives in your landscape, consider this: the general rule of thumb is that young trees will be killed in the winter when the temperature drops below 25º F, small branches on mature trees will die when the temperatures drop below 22º F, mature trees can be killed to the ground in the winter when the temperature drops below 15º F.
The top variety to try is ‘Arberquina’. It has very good cold hardiness, grows 12-15 ft. tall, is self pollinated and is the one that has seen the most success in Texas. The oil from it is very sweet and the fruit can be brined.
For table olives, try ‘Arbosana’. It is rated moderate for cold hardiness and needs ‘Arberquina’ for pollination.
