Any North Florida resident who has tried their hand at growing apples, peaches, or plums may occasionally find themselves frustrated by a year (or two…or three) with a poor or nonexistent harvest. What has gone wrong? Are the trees getting a disease? Were they not fertilized properly?
It may be that the tree owner has done everything correctly, but the weather is actually to blame. The answer to “what has gone wrong?” may lie with a concept called “chill hours”. Plants that are adapted to living in colder climates need some way to figure out when the winter is over. If a plant starts blooming too early, it’s likely that a frost will come along and knock out this year’s flowers. No flowers, no fruit. For a plant, this means no little baby plants this year to keep the species going. To avoid this, some plants have figured out a way to detect and keep track of how cold it’s been in a particular year. When enough hours of cold weather have accumulated, that’s usually a safe signal that spring must be near. This means it’s time to blossom when the weather next warms up.
Usually. Different varieties of plants are adapted to blossom at different times of year, depending on the average amount of cold weather the area they live in gets each year. A plant from a colder climate might not start growing flowers until it has detected 1,000 hours of cold…or more! Given that the temperature range that counts as a chill hour is around 32-45 degrees Fahrenheit, you might correctly guess that such varieties will NOT do well in Florida. In north Florida, we receive somewhere from 500-700 chill hours each year. This winter (as of February, 2023), we have received 479 chill hours in Walton County.
Chill hour total for Walton County, as of Feb 1, 2023
That’s not a lot, and we may not get much more weather that plants recognize as cold enough to count. Apple growers with varieties that need even as few as 500 chill hours may not be making many pies this year. So what can be done?
First, temper your expectations. Understand that even though we may get the occasional hard freeze, it may not count any more toward the chill hour requirement than temperatures just above freezing. Then, when it warms up the following week, those 70 degree temperatures may actually set BACK the chill hour clock for some plants.
Second, choose varieties that require few chill hours in the first place. A ‘Honeycrisp’ apple, needing 800-1000 chill hours each year, is probably never going to produce fruit in the panhandle of Florida. Other apple varieties might, though! Try varieties such as ‘Anna’ (which needs only 300 chill hours), ‘Dorsett Golden’ (250 hours), or ‘Tropic Sweet’ (300 hours). For peaches, try varieties like ‘GulfAtlas’, ‘Gulfcrimson’, or ‘Gulfsnow’ (400 hours each).
Third, consider learning to love other types of fresh fruit. Persimmons, figs, kumquats, and loquats may not show up very often in treasured family recipes, but they can offer a tasty alternative to plants that simply might not be well adapted to our climate.
Peaches are popular, but they may not produce fruit every year!
For more information, try these links:
To calculate how many chill hours your specific area has received, check out the tool at agroclimate.org.
Arapaho blackberry has chill requirements that match those received in our area. Photo by Beth Bolles, UF IFAS Extension
Many of us are enjoying warmer temperatures this winter, but many deciduous fruit crops really need cold temperatures in order to break dormancy for the year. In areas that experience cold temperatures, plants have evolved the ability to survive by slowing growth and protecting sensitive tissues by going dormant. In order to break out of dormancy and begin growth again, plants experience an amount of chill hours (temps between 32 and 45 degrees F) that is suitable for specific areas. In our area, we normally range between 400 and 600 chills hours.
If we choose a fruit plant whose chill requirements match the amount of chill in our area, the plant will generally resume growth when it is safe for buds and tender tissues to develop. If we choose a plant with chill requirements higher than the amount our area receives, then the plant is not signaled to break dormancy and we end up with very sparse growth and no fruit.
So far in the winter of 2016-17, some areas have not received ‘normal’ amounts of chilling temperatures. Common fruit like apple, peach, some blueberries, and certain selections of blackberries may be affected by this by not breaking out of dormancy. This can impact your flower and fruit formation. For commercial growers, it can impact the amount of fruit available and even fruit prices at markets.
Since fruit trees are an investment of time and money, these are not plants that can be easily replanted to match chill hours with changing weather patterns. Perhaps planting fruit crops with a range of chill hours required might be beneficial Your future decisions to grow fruit trees may include crops that don’t rely as much on chill hours to be successful. For more information, please consult the Dooryard Fruit Varieties guide from UF / IFAS Extension.
