Effect of Cold Temperatures on Fruit Set
In California avocado groves, cool temperatures before and during the main period of bloom can have an adverse effect on avocado production. Cold temperatures can:
- Delay flower development
- Lead to poor fruit set
- Result in smaller fruit
- Spur excessive growth on avocado trees
Cold temperatures affect avocado tree pollination
A shortage of bees and a lack of female phase flowers is often a recipe for a poor fruit set. Managed honey bees are usually the best pollinators for avocado trees, as the grower can easily introduce very large numbers of bees for the most effective transfer of pollen to the orchard. When it’s 63 F or cooler, honey bees are less active and less likely to leave the hive to pollinate avocado flowers.
While avocado flowers will continue to open despite cooler temperatures, the female flower phase becomes increasingly shorter and the flowers become less receptive to pollen.
Poor fruit set leads to excessive avocado tree growth
When an avocado tree has a poor fruit set, it tends to begin growing excessively in response. Growers are often tempted to prune back this excessive growth — but they should not. A hard prune of excessive growth does not cause the trees to stop growing — it, in fact, spurs further growth causing the tree to grow taller and the branches longer.
In general, rather than pruning trees that have failed to set fruit, the grower should fertilize the trees lightly, if at all. Limited irrigation — without causing water stress — can also help limit tree growth in these circumstances.
Pulling or bending branches down so the avocado tree growth is more horizontal than vertical, can sometimes be useful but is often not practical due to the large amount of labor needed. Girdling at the right time may be the best option for very healthy trees — this may force the strongly growing shoots into flowering mode for the next year.
Once the trees have fruit on them again, a judicious post-harvest pruning of the tree can help reduce tree size. From start to finish, returning the trees to a more acceptable size and good production could take more than two years.