Self-pollinating peaches (Prunus persica) are a favorite choice for backyard fruit growing. Because they are susceptible to several pests and diseases and are relatively high maintenance, requiring a lot of watering and pruning, peaches are not the easiest fruit tree to grow. However, provided the right temperature range, they can be a fulfilling addition to the garden.
Peaches are happiest in temperate climates, where they will get sufficient “chilling hours” -- temperatures below 45 degrees Fahrenheit -- but won’t be exposed to temperature extremes in either direction. Though U.S. Department of Agriculture plant hardiness zone range depends on species, common fruiting varieties for the home garden such as the dwarf “Reliance” are hardy to USDA zones 5 through 8. In their normal hardiness ranges, peaches respond to the shortening days and cooling weather of fall by going dormant.
Once dormant, peaches will stay like that until they have experienced sufficient chilling hours. These hours vary depending on cultivar. While large golden-red “Red Globe” requires only 850 hours, late-blooming “Canadian Harmony” needs 1,000. Critical low temperatures range according to species, as well as according to the stage of bud swell. While peach tree buds are fully dormant, they can withstand much colder temperatures than after their buds have started to bloom. Before bud break, however, they can often withstand temperatures down to -12 degrees, while “Reliance” can survive -25.
Killing Cold Temperatures
This can range from bud to bud even on the same tree. Because of this, Washington State University conducted a study to find out which low temperatures were likely to kill 10 percent of buds, and which were likely to kill 90 percent. Whereas 18-degree temperatures killed 10 percent of trees in their first bud swell and 1-degree temperatures killed 90 percent, trees in their post-bloom stage were considerably hardier: A chill of 28 degrees killed 10 percent, while 25 degrees killed 90 percent. This indicates that if you live in an area where below-freezing temperatures are possible, you must be willing to protect blossoms by covering them during a freeze, or you should not bother growing peaches at all.
The main consideration with high temperatures is that peaches will not receive the required cold treatment they need to flower and fruit effectively. If you live in a warm area, choose a tree with a low chilling requirement or you will never get enough cold weather to make peaches bloom and grow effectively. In areas with colder winter weather, watch out for peaches with a short chilling requirement: Once completed, they will come out of dormancy during a spell of higher temperatures, after which further cold weather could kill the buds.