How Many Years in Dogwood Years?
Guest Article for the Tallahassee Democrat
March 25, 2016, Release for the Tallahassee Democrat
Dogwoods, yep they can be one of our best flowering plants. I can remember seeing rows of them flowering in concert with an understory of azaleas lining our suburban streets. It was a site to behold. Sometimes it almost looked cartoonish to me with the profusion of colorful flowers. Unfortunately, this seems to be coming a less common site to us. Our eastern dogwoods (Cornus florida) seem to be not doing well.
So what is going on? Many people tell me they heard it is “the blight” or “dogwood blight.” This, like usual, is rooted (no pun intended) in some truth. There is a dogwood anthracnose caused by the fungus Discula destructiva that has been destructive to dogwoods in the Southern Appalachians. Fortunately for us, research shows that our hot summers are too much for this type of anthracnose (there are many kinds) and this dogwood blight is not a problem here. Dogwoods still have many organisms that attack them, but none of them are new.
As we delve further into the cause of our declining dogwoods, I would like to make a point. While trees can die from one thing, more often it is many things that will do a tree in. I think this is the case for our dogwoods.
Often before a biological organism, such as an insect and/or a fungus attack a tree, the tree is first stressed by an abiotic agent. Examples of an abiotic agent would be a lightning strike, flooding, improper application of an herbicide, or mechanical damage to a root from a lawn mower.
Our dogwoods often suffer from a plethora of abiotic stresses brought on by humans. Common ones include lack of mulch, injury by lawn mowers and weed whips (mulch would prevent the need to cut grass in these areas), soil compaction, improper pruning, and the list goes on. But I have to admit, when the dogwoods were doing well, many people were doing these practices, and while not helpful, our dogwoods still persevered.
Without a new bug or bad cultural practice by humans, I believe I have narrowed it down to one thing: weather. Eastern dogwood grows farther south than here, but it becomes increasingly rare. As a plant grows naturally on the extremes of its natural range, you often find that these locations mimic an environment more like areas within the range where it is more abundant. I see this with spruce trees in the Southern Appalachians, as they follow the path of a cool stream that moderates climate at lower elevations. Typically, they are much more abundant in cooler temperatures to the north.
If you recall over the last 20 years, we have had some extreme dry and wet years. Also some unusually hot summers, which can be a great stress to a tree at the southern end of its range.
If you add this stress to the already abundant biological stresses that have been around for many years, you get a devastating blow to our dogwoods. Add this to the aforementioned cultural practices that we unfortunately inflict, and we begin to see the results that we are seeing with our dogwoods.
Finally, I would like to add that the ability of a plant to deal with stress decreases with old age. Dogwoods were really popular about 35 to 40 years ago, and so many were planted. That is about how long they can live.
So, my advice at this point, is first to use dogwood substitutions such as southern crabapple (Malus angustifolia), redbud (Cercis canadensis) and fringe tree (Chionanthus virginicus). Diversity creates a more resilient situation than having monocultures of our best known trees (crepe myrtles, live oaks, etc.). Second, treat our dogwoods as best as we can with good cultural practices. Maintain mulched beds two to four inches deep and spread them out at least as far as the crown. Don’t pile the mulch up deep against the trunk. This allows the tree to recycle its nutrients from the leaves that fall into the mulch. Mulch also ameliorates soil temperatures and helps build the soil to better retain soil moisture. This provides for the tree a more moderating soil environment during extreme weather.
Stan Rosenthal is a forester with Big Bend Forestry and is a volunteer writer and retired Extension Agent with UF/IFAS Leon County Extension. For gardening questions, email us at firstname.lastname@example.org