Each spring, fruit trees begin waking up from dormancy as temperatures reach a minimum temperature threshold for development.
As spring progresses and temperatures continue to meet or exceed that minimum threshold, buds on the trees begin to swell and burst open, revealing green vegetative tissue as well as clusters of small flower buds.
The trees’ first leaves expand and pedicles attached at the base of the flower buds distend while flower buds also begin swelling, and although buds are still closed, hints of flower petals become exposed. In fruit tree jargon, this stage of development is called whitebud or popcorn because the flower buds resemble popped popcorn kernels.
The transition from popcorn to bloom occurs rapidly, potentially within hours, when temperatures are warm. Conversely, progress from popcorn to bloom may occur more slowly if temperatures are cooler.
After this year’s long, harsh winter and an ongoing cool, wet spring in northwest Michigan, we are finally seeing blooming fruit trees in our landscape. Early blooming stone fruits such as apricots and plums displayed blossoms around Mother’s Day and some earlier developing sweet cherry varieties such as the light sweet cherry variety, Emperor Francis, opened up blossoms late last week.
By mid-week, most sweet cherries were blooming across the region.
Currently, development of tart cherries is variable across the region — in some Leelanau County orchards flower buds are still closed and in some Antrim County orchards tart cherries are blooming. Pedicles are distended and flower buds are evident on many apple varieties while later season apple varieties such as Northern Spy are just beginning to show vegetative tissue and clusters of flower buds.
Fruit tree development is dependent on environmental factors, and as many of us have experienced, those factors such as temperature, humidity, sunshine or rainfall, seem to change at the drop of a hat in Michigan. As a result, bloom time varies within orchards, among orchards, and from year to year, making the task of estimating the occurrence of bloom and harvest very difficult.