I’ve heard from a number of local residents that their trees started to bloom this fall instead of the normal time in spring. Personally, I’ve seen peaches, plums, and pears with a few blooms. To explain it briefly, our summer drought stress caused some trees’ growth to slow or stop. Growth then resumed late in the summer when rains came and relieved this stress. When growth began again, some of the flower buds which would normally bloom next spring, began to grow and develop, and we experienced a fall bloom.
Taking a deeper dive into the cause of this marvel, flower buds are formed in mid-summer for almost all of the fruit crops for the following year’s crop. All buds start out as leaf buds but some convert to fruit buds, a process called floral initiation. This process is irreversible since flower buds cannot revert back to leaf buds. The timing of floral initiation differs for the various types of fruit, but usually occurs throughout the summer months and varies a little from year to year, depending on the species, the variety, and the environmental conditions.
Every experienced fruit grower knows that each year, we are responsible for two crops: the current year’s yield and setting up for the following year’s harvest through proper fertilization and irrigation. We prepare for the coming year with proper pruning, irrigation, fertilization, and pest control.
Getting a little technical, there are several types of dormancies in plants. Ecto-dormancy is when the external conditions are not good for growth (‘ecto’ is Greek for outside, external). This can be brought on by drought, or the short days and cool temperatures of fall. Through the winter, the trees enter endo-dormancy and internal influences limit growth even when conditions are good for growth.
During the winter in endo-dormancy, the tree tracks temperatures just above freezing to monitor the progress of the winter. This tracking of cold temperatures is called “chilling”. If you have ever studied what fruit trees best produce in your area, you have undoubtedly studied the chilling hours for your region as well as for the varieties. In Angelina County, the average chilling hours are 600, with an anticipated range from 450 to 700 chilling hours. (You can search online or call your local County Extension office to find the chilling hours wherever you live.)
It is this chilling requirement that usually prevents the tree from beginning growth during warm periods in the fall and winter. There can be further development of the buds if the winter is exceptionally warm, but the buds do not flower until after the tree begins spring growth. After the tree passes through winter, flower development within the bud is completed in spring as growth begins.
So, what caused flower buds, which are normally inactive at this time in the season, to begin growth and bloom this fall rather than stay dormant through their winter chilling?
It is not unusual to see bloom in trees that have been drought-stressed in summer and then get good moisture later in the growing season. This year, most of Texas had good spring moisture. Trees grew very well in spring and developed accordingly. Because our part of the world was not only incredibly dry, but also saw record-breaking high temperatures, there was an enormous increase in the trees demands for water.
Those hot and dry conditions quickly exhausted any available soil moisture in the surface soil where most of the roots are taking water. While the tree’s energy was focused on surviving, any new growth would have slowed or stopped. Later, when water was readily available again, growth resumed. Some of the flower buds received a signal to start growth and, thinking it was spring, finished their development and bloomed.
When drought causes spring blooming plants to bloom in the fall, those buds aren’t available to become flowers in the spring. Depending on how many buds open early, out-of-season flowering could reduce blooms in spring gardens and even reduce harvests.
For peaches, plums, or pears, there’s not much concern about fall blossoms because thinning fruits is recommended anyway. But for crops like blueberries, where growers want every possible bud to lead to fruit, fall flowers mean fewer berries to enjoy in the following year.
If fall blooming becomes a persistent problem, people may need to help their gardens and orchards with supplemental watering, particularly during late summer. Mulching around trees is also a fantastic practice to retain moisture and regulate soil temperature throughout the hot and dry summer months.
