The dogwood tree (Cornus) is a celebrated ornamental plant across North America, known for its layered branches and striking seasonal transformations. Its arrival signals the shift from late winter to spring. The bloom period is a flexible window that varies significantly based on both geography and species.
The Core Timing of Bloom
The native Flowering Dogwood (Cornus florida) provides the baseline for the spring display. Blooming begins in the Southern United States as early as mid-March and progresses northward as temperatures rise.
In the mid-Atlantic and central states, peak bloom generally occurs throughout April. For northern regions, such as New England and the Great Lakes, flowering may not begin until late April or early May. This progression means the dogwood bloom spans over two months across the country, starting in the South and concluding in the colder regions.
Environmental Factors Driving Bloom
The variability in bloom timing is driven by physiological requirements that must be met before flowering can begin. Dogwoods require a specific duration of cold temperatures, known as chilling hours, to break winter dormancy effectively. These hours, typically accumulated when temperatures are between 32°F and 50°F, are necessary to deactivate growth-inhibiting hormones within the buds.
Once the chilling requirement is satisfied, the trigger for bloom is the accumulation of spring warmth, measured using Growing Degree Days. The tree needs accumulated heat, often calculated by summing daily temperatures above a 40°F baseline, to push the flower buds into development. If a late-season freeze occurs after the flower bracts have begun to emerge, the tender tissue can be damaged, resulting in browned or aborted blooms. This interplay between necessary winter cold and sufficient spring heat determines the exact week the display begins.
Species Differences in Bloom Schedules
Not all dogwoods bloom simultaneously. The North American Flowering Dogwood (Cornus florida) is one of the earliest to flower, with its showy bracts often opening before the leaves fully emerge. This early timing positions it as a primary flowering tree of spring.
A later-blooming counterpart is the Asian Kousa Dogwood (Cornus kousa), which typically flowers four to six weeks after the native species. Kousa dogwoods often wait until late May or June, after their leaves have fully expanded, to display their flowers. This difference extends the overall dogwood viewing season into early summer.
Duration and Appearance of the Display
Once the bloom is underway, the visual spectacle typically lasts for a period of two to four weeks. This duration is highly sensitive to weather conditions; cool, overcast conditions tend to prolong the display, while intense heat or strong winds can cause the flowers to fade quickly.
The large, four-parted structures that create the iconic display are not true petals but specialized leaves called bracts. These colorful bracts (white, pink, or red) attract pollinators. The actual flowers are the small, often inconspicuous, yellowish-green clusters grouped together at the center of the four surrounding bracts.