Documents: Regional Gardens (Canada) - Prairie:

Japanese Maples & Rhodos

What is happening to Japanese maples—dying branches etc.; should Rhododendrons be wrapped in Caledon; and what trees won’t push up the driveway pavement?
by Art Drysdale
by Art Drysdale

email: art@artdrysdale.com

Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at http://www.artdrysdale.com


October 29, 2006

The three Japanese maples in the photo above are in what we call our raised side garden and they exhibit wonderful fall colour annually; while below this cut-leaf version nearby is this stunning red colour as I type this on October 27. Author photos.

Judy Weisgerber of Nanoose Bay, just down the Island Highway from my home in Parksville (although the problem applies equally to gardeners in virtually all areas of Canada) wrote the following on October 14th. “I was watching the Shaw Community Channel today and saw you talking about trees with color and I wondered if you could give us some clue why our Japanese maple is dying a slow death.

“This tree was purchased in the spring of 2003 and was fairly mature. It had a huge root ball and the first year it flourished. The next year it showed no signs of trouble in the spring but as the summer progressed some of the branches began to die. We took them to the nursery and they could see no reason why as it seemed to be healthy. We thought it might not be getting enough water so we gave it more. The next spring the same scenario took place - it came into leaf and looked great but gradually over the summer more branches started to die and we cut them out. This year, as with the previous springs, it seemed to be doing fine and once again it looks like more branches are dying. I have a friend who has the same problem with her maple and she has had a person out to look at the tree but has had no answer. Her tree is 30 years old.

“Any suggestions you could make would be appreciated. At this point we are contemplating the removal of the tree which won't be easy.”

Unfortunately, many Japanese maples seem to be suffering from at least two different ‘diseases’. The most common, I believe, is a wilt called Verticillium, but even that is subject to some conjecture as you will see. Here is what I have written most recently about this pathogen.

“Japanese maples, at any age, do some times come down with a wilt disease that is found in other larger maple species as well. There is not, as far as I know currently, agreement among the scientists as to what causes it. Some-times it is said to be caused by Verticillium alboatrum, while others say it is the result of Verticillium dahliae. The tell-tale marker of V. alboatrum, most agree, is a discoloured ring-like area in the sapwood that is a fairly obvious olive green colour. To see this you must make a cut with sharp pruning shears across a branch that has recently succumbed; you will then notice an olive-coloured ring just inside the bark.

“Even from my limited experience (including two on our present property here in British Columbia, and several on a friend’s property in Toronto), I have observed the olive-green rings. There seems to be little one can do to stop the disease. Certainly cutting out all branches that show signs of wilting, and doing it long before the leaves actually fall off, is the best recommendation. It is best to destroy such cut wood by burning or disposing of it in the garbage. Some scientists think feeding the tree with a high nitrogen soluble fertilizer (such as BioTLC’s Liquid Growth Early Spring Lawn Fertilizer 18-3-3) by spraying it on the leaves and branches (with the supplied pressure sprayer) several times beginning in early spring, will have a positive effect.”

The other pathogen that listeners/viewers/readers of mine have come upon recently is the regular drying up of the leaves on the upper branches by mid-summer. This, at first descriptions, sounds like physiological leaf scorch which is quite common to Japanese maples, especially in hot summers when rainfall or irrigation is scarce. However, it can also be a disease known as Cristulariella depraedens for which the only ‘cure’ appears to be regular sprays of a copper fungicide (still available at most garden centres). However, in Judy’s case it seems to me Verticillium is the most likely cause.

Norma Parker of Caledon East, Ontario wrote with a question that is close to my heart: “I am a virgin gardener, who has bought a house with a mature, mostly perennial garden surrounding it. We have what I believe to be, fairly mature rhododendrons which bloomed gloriously this fall, after not been wrapped for the winter, but I have been since told that they should have been wrapped, but because of last years mild winter...I got lucky!! Is this so? Should I be wrapping the bushes? If so, when? And when do you remove the wrap? I have found burlap in the "potting shed" and figured this is what I should have used.....any and all help would be appreciated. Cheers."

First Norma, I assume though you wrote “bloomed gloriously this fall,” that the flowering actually occurred this past spring. Although rhodos do occasionally re-bloom in late summer and fall, that is not the usual case! Now, as to covering them with burlap, I am sure many gardeners would recommend that you do so. It really depends on how naturally protected they are; i.e. shielded, especially on their west side by large trees, particularly evergreens. Personally, since they came through last year, I would not cover them this winter, and hope for the best. Or, a half measure you might try is to erect a metre-high burlap screen on posts on the most exposed side(s). It should likely be two or three layers thick. Such a screen can go up at any time, and come down in late March.

If you decide to wrap them in burlap individually, again you can use stakes to make it easier to wrap the plants. If wrapping individually I would not do it until at least mid November, perhaps even later. If there is a possibility of the ground freezing hard, then by all means pound the stakes in anytime now, and install the burlap later. [It is very ugly, in my opinion!]

As I have written and broadcast so many times, I believe wrapping evergreens is a way overdone, particularly by the trade and contractors, who often only do it to get another call-back or fee from their clients; homeowners see-ing this then copy the technique thinking it necessary. It generally is not.

Alan Hart of nearby Errington, only a few Ks from us here in Parksville, writes: “I am one of 19 owners in a mo-bile home park at Englishman River Falls. When the place was developed a few years back, the original owner planted some trees in the boulevard that runs the length of the property. There are eight trees, in particular, that have become a problem. We believe that they are an alder, and find that the roots "go forever" and are actually heaving up the edges of the asphalt which could be an expensive repair job and we feel we must replace them. Can you suggest a replacement tree that does not have this destructive root system that will grow to about 15 to 20 ft. high and has some colour in the fall?”

Suggesting trees to fit specs is a difficult assignment, Alan. First, your likes might be quite different to mine. But, let me outline a couple of points about large tree roots, of which there are three basic types: the tap root that basically grows straight down (examples are oaks, nut trees and pines), heart roots which grow horizontally but generally are drawn downwards, and finally the ever-so-common flat roots, of which the maples are the best example. I believe it is the latter roots that you have interfering with your pavement Alan.

From your question, it sounds to me that you are primarily interested in small trees which rules out quite a few that produce a good fall colour. I would certainly consider sourwood (Oxydendron arboreum) which has summer flowers (white) and excellent reddish fall colour, ‘Little Gem’ Magnolia, Fringetree (Chionanthus sp.) primarily grown for its mid-spring white flowers, Smokebush (Cotinus coggygria) of which there are a number of different cultivars and leaf colours (reddish, green and yellow) or Kousa dogwood (Cornus kousa).

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