Deciduous dogwood trees, such as the flowering dogwood (Cornus florida) and the Chinese dogwood (Cornus kousa), signal the end of their growing season by displaying spectacular autumn color before shedding their leaves. This vibrant seasonal transformation is a predictable, genetically programmed event. The timing of the color change and subsequent leaf drop is a direct response to environmental cues, preparing the tree for winter dormancy.
Typical Seasonal Timing
The seasonal pattern for a healthy dogwood begins with the onset of fall coloration, usually starting in late September or early October. This initial change transforms the green foliage into shades of pink, burgundy, orange, and deep red, a process that takes several weeks to reach peak vibrancy. For the flowering dogwood, this fall color often persists on the branches well into November.
The bulk of the leaf drop generally occurs from late October through mid-November under average climate conditions. Leaves begin to drop gradually after reaching their full autumn color. The process is accelerated by the first hard frost, significant winds, or heavy rain events. Although the leaves turn color relatively early, they often remain attached, providing sustained autumn interest before the final drop.
The Biological Mechanism of Leaf Change
The process of seasonal leaf change and drop is known as senescence, a highly regulated form of programmed cell death in the leaves. This progression is initiated primarily by two external signals: the shortening of daylight hours and the onset of cooler nighttime temperatures. These environmental cues trigger hormonal and chemical changes within the leaf tissue.
The first noticeable change is the breakdown of chlorophyll, the green pigment responsible for photosynthesis. As the tree prepares for winter, it stops producing chlorophyll and begins to reclaim valuable nutrients, such as nitrogen, stored within the pigment molecules for use the following spring. Once the dominant green chlorophyll fades, the existing carotenoids and xanthophylls become visible, revealing yellow and orange hues.
The brilliant red and purple colors characteristic of many dogwood cultivars are caused by the synthesis of anthocyanin pigments. Unlike carotenoids, anthocyanins are newly created pigments produced just before leaf drop. Their production is intensified by a combination of warm, sunny days and cool, non-freezing nights.
Following nutrient reclamation, a specialized layer of cells called the abscission layer forms at the base of the petiole, where the leaf stem meets the twig. This layer seals off the leaf, cutting the flow of water and nutrients. This action causes the leaf to detach cleanly from the branch.
Environmental and Cultivar Variations
While the internal biological mechanism is consistent, the exact timing of leaf drop is significantly modified by external environmental factors and genetic differences. Geographical location plays a role; dogwoods in northern states often begin to color in late September and complete their drop in October due to earlier, cooler temperatures. Conversely, in southern regions, color change may begin in October, with leaf drop extending into early or late November in milder climates.
Environmental stress can also drastically alter the timeline. Severe summer drought or nutrient deficiencies, for example, can trigger premature senescence and leaf drop as early as August. The tree sheds its leaves prematurely in an effort to conserve water and energy, a survival mechanism.
Species also exhibit variation: the native Cornus florida tends to color and drop its leaves relatively early. The Chinese dogwood (Cornus kousa) often begins to color later but may hold its foliage for an extended period, sometimes well into November. Observing the specific response of a dogwood to its local conditions provides the best indicator of its individual seasonal schedule.