Farm Progress

Lack of winter chill temps a concern for fruit growers

Apple growers in Texas, New Mexico and Arizona say winter chill hours, loosely defined as the number of winter hours the temperature lingers between 32 and 45 degrees, are critical in order for trees to bud. Peaches also at risk.

April 28, 2017

5 Min Read
Apples may be in short supply in the Southwest this year following a warmer than usual winter and limited chilling hours.

If an apple a day really keeps the doctor away, the waiting rooms of physicians may get a little more crowded this summer thanks to unusually warm weather across the Southwest this past winter.

Apple growers in Texas, New Mexico and Arizona say winter chill hours, loosely defined as the number of winter hours the temperature lingers between 32 and 45 degrees, are critical in order for trees to bud. No buds, no fruit is the general rule.

While the variety of an apple, for example, determines the number of chill hours required each year, generally ranging between 250 to 500 hours a winter season, other factors come into play. For example, the number of winter days that temperatures exceed 60 degrees during daytime hours and the number of hours each night temps remain in the “chill hour zone,” are factors.

Here's how it works: As the days become shorter and cooler in fall, deciduous plants stop growing, store energy, lose their leaves and enter a state of dormancy which protects them from the freezing temperatures of winter. Once dormant, a deciduous fruit tree will not resume normal growth, including flowering and fruit set, until it has experienced an amount of cold equal to its minimum “chilling requirement,” followed by a certain amount of heat.

In parts of all three states where apples are grown across the Southwest, chill hours were sufficient on a few orchards, especially those located in northern regions of each state, but overall producers are worried the number of chill hours required by many varieties simply did not happen—not for apples, and certainly not for peaches.


Dr. Larry Stein, AgriLife Extension horticulturist in Uvalde, says fruit trees, such as peach and apple, depend on adequate chill hours in the winter to promote proper physiological growth in the spring, and that simply did not happen across many fruit production areas this year. He said if plants don’t receive the required number of chill hours, the plants are slow to leaf out and this typically leads to poorly developed fruit or no fruit at all. Multiple seasons of inadequate chill hours can kill plants.

This past winter has been one of the warmest on record in many areas, especially across Texas according to Texas State Climatologist Dr. John Nielsen-Gammon.

Stein says fruit trees go dormant for the winter months, but chill hours help to promote hormones that dilute growth inhibitors throughout the winter months. In the spring, when temperatures begin to rise, the tree breaks dormancy and begins to bloom, followed by fruit set. But without the proper number of chill hours, the trigger mechanism that ends dormancy and wakes the tree up in the spring does not work as nature planned.

"Hormones in the buds are telling trees to remain dormant because the inhibitors are still there," Stein says.

In such cases, bloom is delayed and fruit set becomes happenstance. In worst case scenarios, fruit set simply does not occur and the spring and summer growing season is lost until another winter season. Too many warm winters in a row, and fruit trees can actually die.


In the Texas Hill Country, peach production is big business, especially in Gillespie County where Fredericksburg and Stonewall peaches are known far and wide for their sweet taste and flavor.

Jim Kamas, AgriLife Extension horticulturist in Fredericksburg, said this past winter was the warmest he can remember in Central Texas, some say the warmest on record since 1906. Generally by this time of year the countryside explodes in color as the pink of the blooming peach trees contrast with the blue and yellow and red of the abundant crop of wildflowers that can be found there most years.

Most peach varieties in Gillespie County require 800 to 850 chill hours in order to bloom and produce a good crop, but this past winter chill hours across the area hovered around the 520 to 540 hour mark. As a result, Kamas says so far this spring trees are slow to bloom; in fact, many local growers are applying a growth regulator designed to replace winter chill and induce uniform bud break.  But he says it is too early after initial application to know if the regulator will produce the desired result.

Local growers say they remain hopeful that low-chill varieties may still produce some fruit this year, but the higher-chill varieties, which includes most of the sweeter peaches, is a wait-and-see project at this stage in the season. He said within a few weeks producers can open up some of the young peaches that do produce to find out if viable seeds have formed.

On the positive side, area grower Gary Marburger reports strawberries are already bearing fruit, and blackberries are expected to follow in the weeks ahead. He reports both berry varieties are not subject to the same chill requirements as his peaches.

Marburger operates a highly successful pick-your-own farm not far from the Pedernales River. Loyal customers from San Antonio and Austin, both over an hour drive away, generally clean him out of fruit, berries and vegetables in the morning hours. Those customers, along with Marburger, are still hoping peach trees will bloom and set fruit in anticipation of the early variety season, which usually begins in May. He warns, however, as a result of a mild winter, ripening schedules, if they happen at all, will be delayed.

Pecan growers in Texas say it is too early to know if minimum chill hours were reached to produce a good nut crop this year. Pecan growers in the Hill Country say recent rains have spawned hope that adequate ground moisture will bring trees out of dormancy. Nut growers in far West Texas and in Southern New Mexico say more rain is needed as spring temperatures continue to climb.

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