Rhubarb, Elderberry & Boxwood

Questions about rejuvenating rhubarb; elderberry problems; and boxwood for Barrie!
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

July 13, 2008

Above, two shots of Amanda Saunders’ elderberry (Sambucus racemosa ‘Sutherland Gold’). Below, typical foliage of the newer hybrid boxwoods (photo courtesy

Back to questions again this week. For example, Z. Marsden from somewhere in southern Ontario I believe, wrote on June 29th, “When would be the best time to divide my rhubarb? Also what type of soil is best? We have hard clay soil, which we have amended with peat moss and compost from our bins.”

That ties in well with a question about rhubarb that was put to host Charlie Dobbin by ‘Bill’ on my old AM740 programme last Saturday. The caller said the stalks were definitely getting lesser in number and smaller in size. Unfortunately, Charlie did not have an answer but promised to investigate and to report the following week. She ‘kind of’ did that yesterday, but only suggested one Website as the source of all such info, which is not always a good idea because she could not have know whether or not ‘Bill’ had access to the Internet. Besides, I didn’t think the particular site she recommended was necessarily the best one.

The answer, quite a simple one actually, is that rhubarb should never be allowed to grow in one location for more than about five years. After that it needs rejuvenation. That is best done when the clump(s) are dormant, which means the best time for digging and transplanting is in very early spring, or late in the winter. At that time, the soil preparation is at least as important as the actual dividing of the clump(s). The preparation should include digging a hole for each new clump and including plenty of aged manure and/or home compost. Obviously the holes should exceed the size of the newly divided clumps.

Dividing the old clump is not difficult; i.e. you may either pull it apart or simply chop it with a sharp spade or other cutting tool. It is important to be certain that each new smaller clump has at least one large bud, which will provide the beginning of the new clump’s growth. Each new clump should be placed with about 2.5 cm (1”) of fresh soil atop of it. Be sure to space out your new clumps at least 90 cm (3’) apart in all directions.

Once the new clumps show some growth in the very early spring, I always advise placing a bushel basket (or equivalent) over it until the weather warms and/or the plant is tall enough that the covering needs to be removed. And, a little later, if seed heads are produced, they should be removed immediately. Generally, the best advice is not to pick any of the rhubarb the first year after transplanting, at least that’s what I used to do!

Though rhubarb seems to enjoy a decent loam soil, I grew it quite successfully in a very sandy soil in Toronto in the 50s, 60s and 70s.

Though you didn’t ask, I can recommend one cultivar to you that I always found performed well. It was ‘Canada Red’. Now, rhubarb faces the same ‘cultivar problem’ that so many plants do. If you were to obtain and plant all the different ‘Canada Red’ cultivars from different growing nurseries, you would doubtless notice a large variation in growth habit and quality of the stalks. I can only add that you should purchase solely from a reliable garden centre. Good Luck!

On July 6th, Amanda Saunders of Edmonton wrote to Donna Dawson about a major problem with at least one elderberry shrub. Here is her question: “My name is Amanda Saunders and I live in Edmonton here and my husband and I have a fairly new garden, just 3 years old now and anyway, we had two Sutherland Elder bushes and one appears to have died and the other one appears on its way to the same fate. What happens is the new leaves come out all curled up and shrivelled, then turn black, so just wondering if you had any idea what would be causing this. I have tried to find something on the internet and cannot locate anything. I have attached a couple pics of the bushes for you to see oh and also of our backyard as we are very proud of it!!! Thanks so much for your time.”

As you can see from the accompanying photos, which Amanda sent, the one shrub is a mess and likely is dead. My response was as follows.

“I’ve been involved with growing various Sambucus for years, starting in the late 1950s. I have never experienced the die-back your plant seems to have shown. My ‘bible’ for such problems is and always has been Pascal P. Pirone’s book Diseases and Pests of Ornamental Plants. It is the fifth edition that I believe is still the most current. Now, we have to keep in mind, Sambucus racemosa ‘Sutherland Gold’ is a relatively new plant (developed on our Prairies actually) that was introduced after the book was published.

From what I can see, Pascal identifies mainly Cankers such as Cytospora sambuicicola and C. chrysosperma as well as a Diplodia and two additional cankers that can cause major problems The canker girdles the affected branch or branches and the rest of the stem or branch dies. Your photo of the one ‘dead’ shrub is a little too far gone to be able to look for that. How-ever, you should be able to look for cankers on the other shrub, especially if, as you say, it is showing signs of succumbing as well.

The only control for this type of infection, as is the case with many cankers, is the total pruning out of any and all affected parts, and placing them in garbage (not in compost, and I would not even burn them on your property).

If the other shrub dies as well, I would also remove it and definitely not plant another Sambucus in the garden.

Sorry I am unable to give you any better news!

Finally this week, and also from July 6th, Diane V. Brown wrote: “I am currently living in Barrie, Ontario. Not one of the milder cities in Canada, for sure. Moved to this location only last year. Have been putting together ideas to make this home my own. One area that is kind of isolated but sunny, measuring approximately 20 feet by 10, I would say roughly, has me thinking to edge in boxwood and putting a small water area in the midst of it. I have been looking at boxwood, grown or ra-ther sold in local nurseries. Most of it says hardy to zone 5 with warnings that the plants could suffer from the cold. Well that is what is printed when I look into boxwood on the internet. Would you be aware of one that is more hardy than zone five or possibly suggest an alternate hedging material?

“Do enjoy hearing about B .C. on your Saturday morning garden program.”

First Diane, since I don’t have room here for a detailed diatribe on hardiness zones (you can see that in various of my comments on my own Website ). The hybrid boxwoods introduced by Sheridan Nurseries, from work done by their propagator (and an old friend), the late Constance deGroot, are considerably hardier than for Barrie. They were introduced in the 1970s and are considered hardy to zone 4 on the 1967 Canadian plant Hardiness Zone Map. The four differing cultivars vary in ultimate height from 75 cm (30”) to 150 cm. These are available from nurseries literally across North America. The smallest one, ‘Green Gem’, introduced in 1973 would be my suggestion.

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