For Pennsylvania’s apple crop, Old Man Winter is looking more like William Tell. But instead of felling apples with a bolt, he’s endangering them with an early bloom.
Yet it’s not the cold alone. It’s more about timing, said Rich Marini, a professor of horticulture at Penn State who specializes in pomology. Warm temperatures advance the development of buds, making the fruit susceptible to frost. If a frost hits and the fruit has flowered, it could be kaput for one of the state’s cash crops.
An unseasonably warm February, the warmest on record, upped that timeline. But, Marini said, a cooler March has put the crop back on track.
“Usually we bloom right around the last normal frost date,” Marini said. “But if we bloom earlier than that, there’s a better chance we’ll have a frost before that time. If we get a frost during full bloom, worst case scenario is it kills all the blossoms.”
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The apple industry accounts for $80 million of Pennsylvania’s economy, and yields more than 400 million pounds annually, ranking the state fourth in the nation for apple production. A lost crop could cost the state millions.
Marini said Pennsylvania apples usually bloom around the last normal frost date. The median date of the last frost in Adams County, which ranks first in the state in terms of apple production, is April 11, according to the National Weather Service. In central Pennsylvania, the last frost date ranges from May 1 to 10.
“From about World War II until about the mid-1990s, bloom dates were very consistent for apples and peaches — we always bloomed within a couple of days of the average,” Marini said. “Since then, though, we’ve seen earlier blooms.”
Popular apple festivals held in Adams County and Virginia, for instance, once were held when apples began to bloom. More recently, Marini has noticed the celebrations occurring earlier to keep up with the shifting timeline.
“So that tells you something,” he said, “that trees on average have been blooming earlier than they used to.”
Yet apples are hearty. Their trees produce more blossoms than needed — each year, they’re pruned to prevent an overabundance of lower quality fruit — so only about 5 percent of the flowers are needed for a good crop, Marini said.
A winter blast of “Frozen” proportions would be needed to wipe out the crop completely. Especially if it’s followed by a period of unusual warmth.
Sir Isaac Newton, a physicist, Marini is not. But centuries later, scientists of all stripes are still learning from falling fruit.
“Just like we don’t like to go from warm to cold, plants acclimate, too,” Marini said. “Evolutionarily they’ve adapted to that and it’s been OK, but right now I think we’re in a period where there’s more variation in the weather and it could create problems, especially for perennial plants that have to make it through the winter.”