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Hydrangea, Mountainash, Knotweed & LIve Chat

Comments on Hydrangea macrophylla cultivars, a PeeGee Hydrangea that needs a tonic; info needed on dying Mountainash tree; Goats and invasion by Japanese Knotweed near Comox, B.C.; & Site’s Live Chat page!
by Art Drysdale
by Art Drysdale


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

August 10, 2008

Above, a shot of a typical Mountainash tree infected with fire blight. Photo courtesy Top Notch Tree Care. Below, four shots of an extensive planting a seeded wildflowers at the City of Nanaimo’s newly developed Spirit Square.

Author photos.

Last Friday, Brigitte of Aurora Ontario wrote with a comment and follow-up question. “Just want to let you know that I have a number of beautiful hydrangeas for the first time in years!! Thanks for your expert advice. However, they flowered on new wood. The old wood had to be cut off--I thought that the old wood would spring shoots again? I do have another question: I have a Pee Gee standard tree in my front landscaping and for many years, it bloomed profusely with big flowerheads. This year, due to the harsh winter (at one point, it was totally buried in snow), many branches died and there are barely any leaves on the branches that are left and it's currently flowering but with the tiniest blooms. It looks quite pitiful. The garden centre told me to buy a plant starter 5-15-5 to fertilize it but I was not sure this is what's needed. Would appreciate your advice on what needs to be done. I would like to salvage rather than replace it as these trees are expensive.”

First Brigitte, the fact that your Hydrangea macrophylla shrubs bloomed only on new wood indicates to me that they must be some of the newer cultivars, such as Endless Summer that I mentioned in the September 30/07 article, or Blushing Bride which is an even newer pure white one. Whether new shoots would appear from some of the older wood (branches) or not would depend on a couple of factors; the most obvious of which is whether that older wood was killed right back or not. The other factors would be snow cover and just how severe the winter was.

Regarding your PG Hydrangea standard, it sounds to me that it really suffered through a bad winter. The garden centre per-son’s advice is basically good, except I would definitely advise that you purchase/use a soluble 20-20-20 and spray it on the branches and whatever foliage there is. I would do this twice between now and the third week of August. If anything will bring back a shrub or tree that is suffering, that will, but the fertilizer needs to be sprayed directly on the foliage, and don’t worry about over-doing it as the excess will drip down to the soil beneath and could be of some benefit to the plants through the root system.

This past week, Ron Eliason wrote to Donna Dawson, as follows: “I have a problem with a Rocky Mountainash tree (shrub?). Some of the leaves and berries are now drying up and the tree appears to be in some kind of stress. Can you tell what the problem is? Thank you for your help.”

From Ron’s description, it may well be that the tree has contracted fire blight, which attacks all genera within the Rosaceae family. While it is often possible to save pear trees (common hosts of fire blight) by cutting out the infected branches, most mountainash trees that I have seen contract fire blight generally turn totally brown within just a couple of weeks, and are soon dead.

If that is the case, the tree should be removed and no part should be composted. Dispose of it in garbage or have a tree company remove it for you totally. If that is your problem, when you replant another tree, you should definitely stay away from other mountainashes, ornamental pears, crabapples and flowering cherries.

It is possible that fire blight is not what your tree’s problem is. As so many folks do, you did not advise us from just what city you were writing. I am thus unable to know just what type of spring/summer you have had thus far. Your problem could just be a lack of moisture. But it does sound like the horrible fire blight.

Madge Veitch, from Innisfil Ontario, wrote on July 29th, with this comment and question: “Hi Art sorry to hear you won't be on the Radio--their loss. My Garden in Innisfil is badly overrun with these stinging little ants. Have you any suggestions on how to get rid of them? Thanks.”

Regardless of what type they are, still the best way of controlling ants in the garden I believe is Wilson GrubOut (from Sure-Gro, Inc.) which is a 22.5% Sevin (Carbaryl) product that comes in a concentrated form, the container for which easily attaches to your garden hose, and you simply spray the product in the areas where the ants are found. It is a water-based product, not nearly as harmful as the old oil-based ones.

Back on June 7, Chip Ross from the nearby Comox Valley here, wrote with an interesting comment and question: “I found your writings on the ICanGarden website and was particularly interested in your comments on Japanese knotweed (Polygonum cuspidatum). Here in the Comox Valley we are becoming concerned about its invasion and are looking at ways to control it. We have tried Herbicides (including direct stem injection, mechanical removal and regular cutting) with limited success. At present we are running a trial using goats which seems to be promising. See

It occurred to me today that we might be able to freeze areas to kill the knotweed roots--I've only heard of it growing in one place (Edmonton - Greg DeGreef) and wondered what its climatic limits were. Do you have any idea where we could find that out? Thanks for your interest.”

Well Chip, that is a most interesting story about the goats. I was a bit surprised to read that you had only limited success using herbicides. I would have thought that Glyphosate (Roundup) would have done better than you describe, if used in the most effective way. That would include using a much stronger formulation (the concentrate diluted at a much lesser rate than recommended) and applying it only to young plants in the spring as they come up in the spring; and, by cutting the plants down and then re-applying it to the new growth that comes back up in the summer.

Regarding where the plant grows the information is not good! According to the U.S. Department of Agriculture the plant grows well in virtually all of the State of Alaska ( )! It might be interesting to be in touch with folks up there! Again, thank you for your input.

Tom Dawson, this past week, pointed out to me that a number of gardeners have made comments and/or left questions on the ‘Live Chat’ page of this site. We had said that I would not be chatting again until September, but since there seem to be so many questions, I thought I had better go there and type in some answers! Look for those possibly as early as this weekend.

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