Can you explain an unusual phenomenon? I thought dogwood flowers had four petals, but I have seen a tree that has anywhere from four to six. Is this normal?
There are dogwood species, such as Cornus mas and Cornus sericea, that lack showy bracts, so I imagine you are looking at a species that develops flowers at the same time as leaves (the true flowers are tiny, and clustered in a button shape in the center of the bracts). Cornus florida ‘Appalachian Joy’ is an example of a dogwood that has supernumerary bracts. The number of bracts can be variable, as with Cornus nuttallii, which can have between four and eight unnotched bracts (the lack of notches distinguishes Pacific dogwood from Cornus florida).
Portland’s Hoyt Arboretum blog has a helpful post by taxonomist and herbarium curator Mandy Tu about types of dogwoods which should clarify some of the puzzling floral anatomy. About the species that bloom and leaf out at the same time, she explains that “the large showy ‘petals’ are actually involucral bracts (essentially a whorl of modified leaves) that have the appearance of flower petals! These bracts likely function to attract insect pollinators, as well as to protect the actual flowers.”
I have a 22-year-old Eddie’s White Wonder Dogwood. It bloomed the first three springs after planting and then stopped blooming until this spring.
It is planted at the edge of a woodland, facing south. It received summer water the first few years, but not since then, because Sunset Western Garden Book advised re: Cornus nuttallii, part of Eddie’s cross: “Give infrequent summer water.”
I did water it more last summer, as it was so hot and dry in our area. And it finally bloomed!
My question–Do you think that the bloom this spring was the result of more water during the summer, or did the tree have to reach a certain age to start blooming each spring?
There are several reasons that Dogwoods fail to flower. Flowering dogwood does need regular water, according to Sunset’s 2001 edition. Other possibilities might be the age of the tree, and extreme temperatures, such as cold, which may kill the buds.
I would suggest continuing to water and see if it flowers again next season.
There is some discussion about dogwoods failing to flower on the forum of University of British Columbia Botanical Garden. Possible reasons include the age of the tree (not applicable in your case), excessive use of fertilizer, cold damage to buds, lack of sun, and more.
The book 1000 Gardening Questions & Answers (The New York Times) has a section entitled, “Why Won’t It Bloom.” Reasons that dogwood may not flower are similar to those described above:
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1. Overfertilizing – creates excessive foliage
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2. Excessive Shade – need at least 4 to 5 hours a day and more sun means more flowers
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3. Frosts or droughts – at the wrong time (Dogwoods need lots of moisture and we have had several years of drought)
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4. Pruning – removing the flower buds unintentionally
A common question gardeners have is when to prune. “When the shears are sharp!” is the often-heard answer. In reality there are a few timing guidelines that do matter.
First of all, certain trees are known to “bleed” when pruned while the sap is rising in late winter and early spring. Maples, dogwoods, birch, elm, walnut and honey locust are the most common.
Bleeding usually won’t hurt the tree, but the pruning cuts are slower to heal which may leave susceptible trees vulnerable to infection. These trees should be pruned right after leaves fall off in autumn.
Cherry trees are at risk from the destructive cherry bark tortrix. The tortrix is attracted to fresh pruning cuts, so cherry trees should not be pruned between May and August when the tortrix is active.
Spring flowering shrubs should be pruned immediately after flowering so that the new growth has time to form next year’s flower buds. Summer flowering shrubs may be pruned in winter because flowers are formed on this season’s growth.
Pruning resources online:
