Musings on Drought, Insects, Animals, Ginkgos, and Conifers
The impetus for this article was the loss of our sole specimen of Abies koreana ‘Kohouts Icebreaker’ due to drought stress. Making this especially painful is the fact that it was the last plant donated to us from the late Dennis Dodge. I remember spotting this plant as I was leaving his Connecticut nursery with about a dozen Sciadopitys verticillata cultivars. After then discovering that he had grafted it on A. firma, it was a given that it was riding with me back to Georgia. That was approximately six years ago. Over the years it looked good – though never vigorous.
I planted it in an area of the Arboretum that is now difficult for me to access, and I had every intention of having it moved to a more favorable spot this late fall. The area has no irrigation, so plants are largely on their own. Several days past, I walked the area and discovered it was DRT (Dead Right There). I suspect I’m speaking to every reader here when I mention that we all lose plants along the way – that is a given. But occasionally, we lose a plant that we are attached to and we have an emotional reaction.
I first came across this fine cultivar way back when the ACS went to the Czech Republic to include a visit to Kohout’s Nursery in Elstra, Germany. The owner, Joerg Kohout, discovered it when he brushed against it with his leg while walking past Abies koreana ‘Horstmanns Silberlocke’. Ever since then, I have admired the form. Loosing this one stung!
All this leads me to some observations…
In the 27 years that we have gardened here, 2016 has been the second worst year for drought. This, coupled with over 70 straight days of daytime temperatures in the 90’s and nights where it never got below the mid 70’s, took its toll.
We’ve generally held that all firs grafted on to A. firma were bulletproof. I do not find this to be the case. Notwithstanding favorable rootstock, some species just aren’t happy here period; especially many of the West Coast species such as A. lasiocarpa. This can probably be linked to heat – both day and night.
The next observation has to do with Abies firma, both as a specimen plant as well as rootstock. As a plant, it receives its best growth and is happiest in wet summers. That is its habitat in Japan. That fact can be applied to rootstock which will also perform better in moist summers. Taking that to the next logical step, firs grafted on to A. firma will be sturdier when summer moisture is made available. The take-away is not to allow them to stay bone dry for extended periods. Remember, when you purchase a grafted fir, you are really buying two plants – what’s in the ground and what’s above ground. Both needs must be addressed in order to be successful.
While on the subject of moisture, another observation is offered.
Supplemental watering during periods of extreme drought can be a tricky balance. If you have ever observed certain broadleaf evergreens, such as Rhododendrons, in the winter, you may have noticed that on very cold mornings, the leaves will droop and shrivel up. This is a defense mechanism to keep the cells from freezing. This occurs because they lose water, just as many other plants wilt. Severe droughts also cause Rhododendron leaves to droop and curl. The pores—stomata–through which the plant loses water and takes up air are located on the underside of the leaves. When the leaves curl, these pores are protected, and the evaporation of additional water is reduced. The curled leaves protect the plant from more water loss.
A similar phenomenon occurs during long, dry summers. Sensing a loss of moisture, as a defense mechanism, plants undergo a process of shutting down as a way to further avoid water loss. If we suddenly come along and hydrate them, it is akin to us taking a shower in the morning. We are saying to our body, wake up. Now the plant is full of water and begins to restart, which requires a considerable expenditure of energy. Once this re-boot is initiated, if we then allow the plant(s) to return to a droughty condition, we sometimes do more harm than might have been done if we had just let nature take its course. As I initially stated, this is a tricky proposition. If we wait too long, then the plant dies. My best advice is if you’re going to water, remember that you have now set the wheels in motion—if you allow the plant to return to its former state, you risk peril.
Before leaving the subject of drought, I have been impressed with just how tolerant large Cryptomeria are to lack of moisture. We have used ‘Sekkan’ and ‘Yoshino’ as a screen for many years. They have never received supplemental water and have flourished. Same for Thuja x ‘Green Giant’ and Thuja occidentalis ‘Hetz Wintergreen’. There is generally less drought tolerance in the dwarf forms, so keep them watered, at least for the first couple of years until they put some roots out. Cryptomeria have become one of the workhorses in our arboretum—I like all of them; Evelyn, not so much. I advise staying away from the juvenile foliage forms such as “Elegans’, ‘Elegans Aurea’ and ‘Elegans Virdis’; they all eventually succumb to foliar disease.
Ginkgo: I would submit that we have one of the more complete collection of Ginkgo cultivars – or so I thought. Last year I began to notice that many of those that I wanted to brag about looked nothing special. As an example, ‘Beijing Gold’ looked nothing like the catalog pictures. I could list dozens more. This year I discovered that I had inadvertently allowed the understock to become dominant and in many cases, was the only plant left. This is easy to do, especially on young plants, which most of ours were. I advise you to keep an eye on the graft union to ensure you keep what you paid for and remove undesired understock. Speaking of Ginkgo, I find that the small plants benefit and perform better when they are kept moist – also some lime. As they mature, they become less finicky. There are also way too many cultivars floating around with some only displaying very minor variations – avoid being lured into having to have every cultivar listed in some specialty catalog. A couple of worthy cultivars to look for are ‘Snow Cloud’, ‘Potters Pete’ (the best narrow selection I’ve seen. It was introduced by University of FL professor Jason Smith), ‘Anny’s Dwarf’ and ‘Sari’ (the only true dwarf I’ve trialed). Last year, Adam Black (Director, Peckerwood Gardens) discovered a variegated sport on our large ‘Saratoga’. We named it ‘The Prisoner’ due to its stripes. Several nurseries have it and we will see if it is at all stable—I’ve yet to find even one. There is a variegated selection floating around from the legendary Joe Stupka that is reportedly one of the best. Several were offered at the ACS national meeting auction.
: This year we were hit for the first time with sawfly larvae on our 5-needle pines. Over the past, we have experienced their voraciousness for 2 and 3 needle species – especially Mexican species such as P. greggii and patula as well as P. sylvestris and Pinus virginiana. On the 5-needle species such as P. ayacahuite ‘Forest Sky’ and P. strobus cultivars, they appeared in early summer as opposed to those attacking 2 and 3 needle forms in late summer/early autumn. It makes it dicey to go away during those periods. Even if you get the first critters, they will often hatch a new batch, so remain vigilant. While I deplore using Sevin, this has proved to be an effective treatment as well as deterrent. If you are lucky and catch them early enough, the foliage might regrow. For those branches that have been totally defoliated, you will need to remove the branch.
Another scourge is Ambrosia beetles. While they rarely ever attack conifers, they can destroy prized hardwoods such as maples, redbud and dog-woods. Since most of you have other plants besides conifers (no conifer ghetto), this can be important. I have observed that in years where the weather and climate have been mild, the incidence of these pests is nil the following spring. 2015 was a good year for us, weather wise, hence we experienced zero losses in 2016. All this to speculate that with the drought, 2017 might be a bumper year for these critters. If you can catch the outbreak on a tree, (which is characterized by little white toothpick-like protuberances poking out from the trunk), early enough, cut just below the infestation and you have at least a 50/50 chance of the tree re-sprouting. On most conifers, this will not work. Be sure and burn the infected material. Pre-treatments such as deltamethrin and permethrin spray have been shown to have some deterrence.
Animals: I have long known that armadillos were slowly headed our way. Having witnessed their destruction in Texas and South Alabama, this has been a dreaded fear. Long time ACS members Jody and Kimberly Karlin recently reported a sighting in their garden nearby in Conyers, Georgia. Our two worst animals have been deer and beaver. Now armadillos!!! I’m waiting for a giraffe to escape from some local zoo or my neighbors’ goats to get loose.
As I come in for a landing, over the past several years we have been conducting perhaps the largest trial ever in the Southeast on the genus Abies (true firs) on their own roots. I am pleased to report that thus far we have seen more successes than failures – west coast firs being an exception. Conclusions cannot and should not be made without at least 5 years (preferably longer) of data. What survived for say three years may suddenly die. More on this in 2017. Yes, Neil Fusillo, I agree, Abies alba does appear to be viable, albeit slow.
Speaking of Neil, congratulations on being elected to serve as our National President. As you all know, Neil resides in the Southeast and will proudly repre-sent our region and the Society.
In conclusion. I know that many of you suffered significant losses in 2016. My advice is to learn from what you experienced and continue on. This year I lost much less than in the early years. That is due in large part to knowing more, and that knowledge came from trial and error. When you fall on your face, you’re moving forward.
About the Author:
Tom Cox served as National President of the American Conifer Society from 2006-2008. He now travels the world in search of conifers that might be adaptable to the southeastern U. S. Along with Dr. John Ruter, he has co-authored a first-ever book on conifers is the Southeast (Cox, Tom, and John M. Ruter. 2013. Landscaping with Conifers and Ginkgo for the Southeast. Gainesville: University Press of Florida.) He and his wife, Evelyn, established Cox Arboretum, in Canton, GA, in 1990.
Excerpt from the December 2016 Southeastern Conifer Quarterly. Gain access to archives of past newsletters and the National Conifer Quarterly by becoming a member of the American Conifer Society.