More Questions & Answers

Hydrangea Issues, Rose Bushes, Storing Calla & Cana Lilies, Potatoes Scabs & Over-wintering Pampas Grass
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

October 5, 2008

Above, Hydrangea macrophylla cultivars such as this blue lace cap in our Parksville garden are definitely not hardy in zone 5 and lower although some of the newer cultivars which produce bloom on new wood (such as H.m. ‘Endless Summer’ are hardy in colder zones. Author photos. Both Cana and Calla lilies require indoor storage even in zone 6 climates. Here a variegated Cana ‘Johannesburg’ is shown growing in our large pond and the new Calla lily ‘Captain Safari’ grows nearby. Author photos. Below, the typical damage from potato wireworm on the tubers and a large specimen of Pampas grass growing here in Vancouver Island.

Back to more questions received by Donna Dawson following her most recent newsletter. This first one is from Sandra Macneil and came in Saturday, September 20: “I have a hydrangea that has grown quite a bit up and out but has not given me one bloom. Do you have any idea what happened? Thank you.” Following a note from Tom Dawson, Sandra added: “We are in a sub division which was once an apple orchard. Plant is between two Hollies. Last year beautiful blooms very large. We live in Cape Breton Nova Scotia. Planted part sun and shade. Plant is three years old bought locally. Soil is acid. When planted did a mix of good soil and compost!”

The only suggestion I can make is that it’s a Hydrangea macrophylla cultivar (blooms would resemble the plants sold in the stores at Easter each year) and that the flower buds (produced on the plant each late summer) were killed during the winter. Since you have not told me your exact location, I am unable to say with any certainty whether or not this could be the cause. The entire east and north coast (e.g. from Hawkesbury up through Louisbourg and including Glace Bay and New Waterford) are considered zone 6a and should support flower buds over the winter on H. Macrophylla plants, but even the city of Sydney is considered to be in zone 5b which could well mean in most winters the flower buds would be killed. So, I need more info if I am to be of any real help; I need to know which Hydrangea species/cultivar you have, and your exact location.

Next was another from Nova Scotia, specifically from Judy Haynes of Amherst and came in on September 21: “In spring of 2006, we transplanted a hydrangea bush from a neighbor and it is spreading well......but, the leaves have been turning black and shriveling up all summer. We had a very rainy summer here in the Maritime Provinces. Also, both years, the bush only had 3 to 4 blooms and after several days, they turned a rusty brown color. Do you think maybe this is a powdery mildew problem or a fungus and do you know what I can do to help it? We planted this hydrangea by our back doorstep and are hop-ing it will grow into a large bush. I have sprayed it with "Trounce" but the leaves still look sick.”

I suspect that the problem has to do with the extremely damp weather you have had. Hydrangeas are susceptible to a bacterial wilt (Pseudomonas solanacearum) for which there is no known control. There is also a possibility that a bud blight (Botrytis cinerea) is responsible. The chemicals for its control are not available to the domestic market. I think your only answer is to hope that next year the growing season will not be as wet. By the way, ‘Trounce’ is an organic insecticide consisting of fatty acids and pyrethrum and is only effective in controlling insects. I doubt your problem is caused by insects.

On the same day, Beverley, of unknown location, but likely in southern Ontario, asked Donna: “My question is about a rose bush that I planted last spring 2007. I cannot remember if we got any blooms from this bush or not last year but this year the stems are so thin that the stem cannot hold up the rose. What do I need to do to get healthier stems next year? The bush itself is lovely and thriving. The roses toppling over are my only concern.”

Weak stems would generally be caused by one of two problems: 1) a generally weak bush; something for which there is no real cure, and most growers just scrap such bushes; or 2) a lack of nutrition, specifically phosphorus and potash, although nitrogen certainly plays a role as well. I would get a good quality granular rose food and begin applications to the soil in April just as growth commences. In addition I would apply a soluble fertilizer with a high middle number (i.e. 15-30-15) about every two weeks once the bush has its full foliage.

Those were followed by this on the 22nd from Amrita Persaud-Tiwari in Toronto--“Thank you so much for sharing such insightful details regarding fall/winter storage of Canna lilies. My calla lilies did not bloom this year. I live in the Toronto area. Also, could you please let me know what is the best way for winter storage of my calla lilies?”

In re-reading your question, I wonder whether or not you are confusing Calla and Canna lilies. Fortunately, their storage over winter in all but the mildest climates in Canada (such as here on Vancouver Island) is essentially the same. Canna and Callas (Zantedeschia) should be dug only after the first light frosts have browned the foliage. They should be allowed to dry in a warmish area for about a week and then stored in a cool temperature. At The Niagara Parks Commission School of Horticulture we always stored the Cannas (after shaking most of the soil off the rhizomes, and cutting the stems right down to the rhizomes) in drawer-like flats on newspaper in a cool basement. While many gardeners suggest storage be in dry peat moss, we did not do it that way simply because if you leave them individually on newspaper, it is easy to check on them every two weeks or so to make sure that are not too wet (causing rot) or too dry (causing total drying out). While in storage, it is best if the rhizomes do not touch each other.

The same essentially applies to Callas although more folks seem to keep them in peat moss. If you decide to go that way, be sure to reach in and check one of the rhizomes regularly.

The rhizomes should be re-planted in flats and watered etc. beginning in mid-February. Keep them cool (not over 10o C) and give them as much light as you can. On warm days put them outside for a short time, out of any wind.

The most recent inquiry came in to Donna this past Thursday and is a vegetable question from Andy Tansowny of unknown location: “We seem to have a lot of scabs on our potatoes, also seems like small black spots that look like small worms have invaded into the potatoes. Would you have any suggestions?”

Potato scab is caused by a soil-borne organism called an actinomycete and occurs generally wherever potatoes are grown. It does not affect the quality of the tuber for eating, although a heavy infestation does make for a lot of extra scraping when preparing the tubers for cooking. There is little that can be done either to prevent scab and certainly nothing once it is noted. Generally it occurs less in slightly acetic soils (pH 5.5 to 6.0), and if strict crop rotation is practiced, it will be less prevalent. The application of wood aches (extremely alkaline) will encourage more scab.

You can try scab resistant cultivars but it (again) is difficult for me to make suggestions when I do not know your location. You should check locally.

The insect damage you mention could be any number of pests which bother spuds. For example, the Colorado potato beetle is very common (try King Bug Killer), but so are wireworms, and white grubs. Check a farm Website (such as ). to help identify which it is you have.

And, finally this week, this one came to me from Cinzia Scalabrini in King Township, northwest of Toronto: “I am appealing to you to find out how to properly winterize two Pampas grass I have planted this June. I believe my hardiness zone is 5a. When I purchased the grass the nursery informed me that I will not be seeing flowers for the next three to four years and that at the end of the season I had to cut the grass down to two inches stump and take it indoor for the winter or it would not survive. I am posing myself, now, all this questions, realizing I do not have the proper answers, and I am writing to you knowing your extensive expertise in the field.

  1. How big does the vase/container have to be?
  2. Which temperature do I have guarantee to the grass? I have an heated garage at 10C of which we do not open the garage door often, but sometimes we do and the light is scarce; just one small window for a two-car garage. Or the house, that during the day offers 15C and the light is, I guess, average.
  3. How much do I water the grass during the winter months?
  4. Would I be able to be successful, considering I have no prior experience with bringing indoor plants, especially Pampas grass?
  5. I wish I had to worry about this now, but...what happens the day the plant is too big to be brought inside? Can I build around the huge grass a greenhouse? Will the Pampas grass survive with winter temperature of -20C?

“I guess that the question No. 5 comes from being concerned about waiting four to five years, doing all the work and sacrific-es to come to realize that one day, your beautiful grass will eventually die because too big and beautiful to be protected. May be I should abandon the idea to have Pampas grass in my garden, or move south! LOL!.

“Truly hoping and wishing this is not going to be the case I anxiously await for your answer. Thanking you in advance for your time and consideration you are giving to my concerns.”

My response to her went as follows: “Did you purchase your Pampas grasses from Humber Nurseries on old Hwy. 50? If not that would be my first suggestion—that you visit them there and check out all the grasses in front of and beside the Peters residence just north of the main Garden Centre entrance. Humber’s people have been featuring those plants for years.

“Yes, all of the Cortadeira species are tender anywhere in Ontario and the usual suggestion is that they be brought into an un-heated garage. Whether yours, heated to 10oC, may be too warm would be a concern of mine. If you could keep it at just about +1 or 2oC that would be better, and it would not matter if there was not light in the area. I would put it into a pot at least 15 cm in both diameter and height (preferably with no sloping sides so that it is much narrower at the base than at the top). Use the same garden soil as is in your garden now.

“You will only need to check the moisture level of the two containers every other week or so, and when they are dry, add a little bit of water—don’t soak them, but don’t let them dry out totally either. You’ll quickly get the ‘hang’ of caring for them!

“I would not think you would want to build “a greenhouse” around the two plants in the ground—a lot of work, and very ugly looking as well as being subject to vandalism.

“My suggestion would be that you drop into Humber Nurseries and talk to someone who works on the grasses. Tom Thom-son, whom I used to interview regularly on my AM740 gardening programme would be the best one, but he is basically re-tired now. Guy Peters or his brother Frans, or their father Frans Sr. would be the best if you can get one of them.”

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