Often called the most beautiful native North American flowering tree, the dogwood (Cornus florida) is a small deciduous tree beloved for its green-yellow flowers in spring that are surrounded by four showy white bracts (petal-like modified leaves). Provided the tree is healthy and not under environmental stress, flowering should occur if adequate light is present. However, diseases, drought, and extreme temperatures in either winter or summer can negatively affect the amount of flowers in spring. Hardy to USDA Zones 5 through 9, excess cold can destroy flower buds in winter and excessive heat and sun in summer can weaken the tree.
Reducing Environmental Stresses
Determine your USDA Plant Hardiness Zone (see Resources). Flowering dogwood is a finicky plant, performing its best in regions that have a similar climate to its native range--the eastern United States. In USDA Zone 5, unusually cold winters or late freezes in April or May can destroy emerging flower buds. Likewise, a late frost in March or April in warmer zones also can nip the flowers, reducing the display.
Monitor the growing conditions for the tree. This species appreciates a moist, non-alkaline soil that has good drainage. Water the tree to protect it from drought stress, and ensure after rainstorms that the roots are not in soggy, waterlogged conditions.
Ensure that adequate amounts of light reaches the tree. Although flowering dogwood tolerates full sun, it naturally is an understory tree, getting light shade and dappled sun under the branches of much taller shade trees in woodlands. Morning and late-day sun is fine, and in hot climates, shade is needed in the hottest part of the summer afternoon. If it gets too little light, the tree will not produce an abundance of flowers.
Fertilize the tree each year with an all-purpose, well-balanced granular fertilizer product that slowly releases nutrients. Follow label directions for appropriate dosage, but make sure not to over-fertilize, as this can also lead to plant stress or an overabundance of leafy growth without setting flower buds. A 3 to 4 inch layer of organic mulch is beneficial under the branch canopy, too.
Seek out advice from horticultural experts in your area. Sometimes certain seed-grown flowering dogwoods have the genetic disposition not to flower well. Or, there may be other factors known in the region to be limiting abundant flowering on the tree this year. For example, an unusually wet, humid spring can lead to flower blight, causing bracts to drop or brown prematurely.
Allow the tree to establish and mature. Newly planted trees are best given the opportunity to acclimate to the new soil and send out healthy roots and foliage, so they have the energy to produce flowers the next spring. Spectacular, across-all-branch flowering may only occur on trees that are well-established, healthy and of considerable size and age.
Examine the depth at which the tree is growing. Most noticeable on younger, more recently planted trees, if planted too deeply, the tree slowly diminishes its vigor by losing leaves, irregular branch dying and absence of flowers. The trunk flare, where the straight trunk widens out to transition into roots, should never be buried under mulch or soil. Sometimes the tree can be dug up and replanted at the proper depth if it is still attractive in shape and growth.
Consider removing or replacing a consistently performing flowering dogwood. Blame it on poor site placement, a diseased tree or just excessively old age for the decline in flowering, but realize planting a new flowering dogwood in the perfect light exposure and soil can create a spectacular specimen to enjoy. New hybrid selections of dogwood may be better suited for your garden's growing conditions.