After two months of unusually warm conditions throughout Indiana, state climatologists based at Purdue University believe temperatures will slowly return to seasonal norms over the next month, which is good news for fruit growers and home gardeners concerned that their plants might be emerging too quickly.
“There is a lot more weather to come before we know what the fruit crop outlook will be, but as of right now things are in good shape and, in fact, a bit more chilling is needed for some fruit crops,” said Bruce Bordelon, professor of horticulture and Purdue Extension viticulture and small fruit specialist.
Bordelon advised growers to be patient, giving trees, bushes and vines more time to get their winter rest.
“The general consensus for now is to delay dormant pruning until a bit later in case there is significant weather to come,” he said
Fruit production is an increasingly important part of Indiana’s agriculture industry. The state ranks 10th nationally in blueberry production at 3.6 million pounds annually and produces 26 million pounds of apples per year, ranking 20th in the country. Together, Indiana apple and blueberry crops have a combined value of more than $13 million.
In addition, Indiana produces about 3 million pounds of peaches each year and is home to a thriving wine grape industry with more than 85 wineries and vineyards statewide.
Fruit-bearing trees go dormant in winter until they register enough “chilling hours” to begin blooming once temperatures exceed 50 degrees Fahrenheit for an extended period. The number of required chilling hours varies by species, ranging from 600 hours for grapes and most peaches to 1,200 hours for apples and blueberries. Three weeks of optimal temperatures can produce 500 chilling hours.
Chilling hours typically occur when the temperature is between 34 and 45 degrees F, with optimal chilling taking place at 42 degrees F.
Daily high temperatures in Indianapolis exceeded 45 degrees F 13 times in January and 15 times in the first three weeks of February. The longest stretch was six days, from Feb. 17-23.
Peter Hirst, professor of horticulture and Purdue Extension commercial fruit tree specialist, says so far temperatures have not been warm long enough to threaten the state’s fruit crop.
“We really haven’t had that much warm weather,” Hirst said. “If we were to have another week with temperatures in the 70s, that would be cause for concern. Another saving grace is that the cool down we are expecting will be moderate and gradual. And we really haven’t had any extended periods of extreme cold this winter so fruit buds are in good condition.”
If the weather gets too warm too soon, fruit trees might start to bud out prematurely, putting them at higher risk of injury if temperatures drop significantly.
That pattern last occurred in 2012, resulting in severe losses to the state’s fruit crop.
Bordelon said that doesn’t appear to be the case this year, noting that forecasters at the Indiana State Climate Office see no signs of a sudden deep freeze that could damage early emerging trees this year.
Ken Scheeringa, associate state climatologist, also with Purdue, expects a moderate downturn in temperatures in March.
“Looking about 30 days ahead, the Climate Prediction Center is forecasting a gradual cooling of these unseasonable temperatures week to week,” Scheeringa said. “By mid-March, Indiana is forecast to have slightly below normal temperatures.”
B. Rosie Lerner, Purdue Extension consumer horticulture specialist, said it is not unusual for some decorative garden plants - daffodils, dianthus and daylilies - to emerge during February warm spells in Indiana.
“The plants will survive just fine,” she said. “The longer the mild weather stays around, the more potential there is for damage when below-freezing temperatures return. Foliage that has popped up may be killed back, but the bulbs and storage roots should remain undamaged underground.”
Kyle Daniel, Purdue Extension nursery and landscape outreach specialist, said as long as temperatures remain at or near seasonal norms, the risk to ornamental species should be low.
“Nursery growers in the northern part of the state shouldn’t be experiencing many species with bud break, but southern nurseries may have bud break on several species,” he said.
“If the warmer weather continues, we could see the emergence of some pest species which may then be killed if we have a freeze,” he said. “If temperatures revert to more normal levels, the effects on insects will be minimal.”
Lerner said growers should rest easier with the outlook for cooler weather in the near future.
“We could be looking at an early arrival of spring, but if the extended forecast is a return to more seasonal temperatures, then the progress toward spring will slow down a bit and that would be good news for all.”