Documents: Special Interest: Seeds, Bulbs & Such:

Sweetpotatoes & Cotoneaster

Growing sweetpotatoes in northern climates; what to do about (fire) burned arborvitae; and training Cotoneaster shrubs for a formal hedge.
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

September 13, 2009

Above, two shots of badly chewed Arborvitae (Cedars--Thuja) here on Vancouver Island. Note even though they have been well chewed, the growth continues, which may apply to the burned plants a Forum-member has. Below two different Cotoneaster growing in my own garden, neither of which would be hardy in Zone 3a. The middle shot here is Cotoneaster hybridus ‘Pendulus’. The final photo shows an unknown species of Cotoneaster trained against a wall here on Vancouver Island. Again, it would not be hardy in a colder zone. Author photos.

There have not been a whole lot of questions this week, but in checking the Forum on this site, I note a couple of interesting ones there, which as yet have no answer. I am not certain I can give an absolute answer, but I’ll try to make a suggestion or two.

First, here is the one question that came in on Wednesday, from Lila at Triple Creek Ranch B&B in Northwestern British Columbia: “Hello: I have a question about sweet potatoes. I bought a sweet potato (orange one) from the store. It grew sprouts so I put in the soil in one piece. A few weeks later it sprouted up and produced leaves. The leaves were purple, until I put some fertilizer to it then the leaves turned green. I have seen photos of sweet potatoes and the leaves are purple. My question is, what colour are the leaves supposed to be? I was told sweet potatoes don't grow here. Ha ha, I know they do now. Thanks for your time.”

As soon as I read this I knew I should send it to Gregg Wingate who runs Mapple Farm, in Weldon, New Brunswick. Gregg is a grower/supplier of certified organic (OCIA & NOP) seed and plant stock. His specialties include: short-season sweetpotatoes, distinctive tomatoes, Jerusalem and Chinese artichokes, French shallots, Horseradish, Egyptian onions, garden soybeans and more. He has a brochure available: a) by request via e-mail, please let him know, though, where you're based (in serving residents from outside Canada they need to pass on some added info); or b) via standard mail, free within Canada with a self-addressed stamped envelope (S.A.S.E.)--please make it at least a 4 by 9 inch envelope with a 54 cent stamp. From outside Canada, send $1 U.S.; Canada Post won't accept U.S. stamps.

Here was Gregg’s response to Lila: “I can think of a number of answers but am not certain which might apply in your case. I too often see sweetpotato leaves, shortly after transplanting, turn purple and then follow with green growth afterwards. I've always suspected that this is the plants' natural reaction to more light than they can handle early on. I'm too busy to give them a more ideal hardening off period but always eventually get away with (what say we call this) Darkening Leaf Syndrome so I don't bother with the extra care.

“Leaves going purple is in general, an indication of lack of phosphorus. Whether that's what's happening before you apply fertilizer or there's simply limited ability for phosphorus uptake when the plants are stressed regardless, I couldn't tell you. One final thought is that some cultivars are more prone to purple leaves than others. I'm not knowledgeable about decorative Ipomoea batata (sweetpotato) types but can tell you that one strain, Tainung 65, I grow usually sports violet and/or bronze foliage in low light conditions.

“Kudos for introducing more Northerners to the joys of sweets.”

Now to this site’s Forum.

Dave, from somewhere in Zone 5, likely in Ontario, writes; “I have an 8-10' tall black cedar hedge that separates my property from my neighbours. It is probably 4-6" wide and straddles the property line. I have burned a portion of the hedge with a weed burner, when the flame caught some of the dead fall at the base of the hedge. The fire burned most of the full height of one plant maybe 1-2 feet in toward the centre. The blackened pieces have been cut off, but will the tree grow back if we keep it watered and well fertilized?”

An unusual problem to say the least. [Is it really just 4-6” wide?] Had it been earlier in the season, I would have suggested fertilizing the surrounding soil with Blood Meal (not Blood & Bone Meal), and, as well, applying a soluble fertilizer such as Cedar Feeder (30-10-10 or similar analysis) to the entire plant. I do think it is a bit late now for that, but you should buy the product and have it ready to apply as early in the spring as possible (after the frost has left the soil). I would not prune any more as in pruning you could easily prune away some burnt-looking but still alive branches.

This problem brings to light an additional problem caused by the enviromaniacs (written about in this column last week) in that most of them consider the burning off of weeds with propane-fired machines as a better alternative than products such as the ultra-safe 2,4-D or the fast-disappearing Glyphosate (Roundup). Imagine considering a portable propane machine as safe! Just ask the folks in the west end of Toronto what they now think about living near a pro-pane facility after it totally blew up and caused the evacuation of hundreds of homes a year ago!

And, from Zone 3, Catherine asked the following: “Three years ago we planted a new hedge of cotoneaster shrubs. They are growing well for the most part, (I had two different kinds, one is doing very well, the second is somewhat stunted). The one with shiny leaves and black berries is doing very well. The other one has smaller leaves of a lighter, not shiny leaf and no berries as of yet, it seems to keep dying back and restarting its growth each spring. I think I will probably replace these ones next year. I am wondering how and when to prune the other kind to create a formal hedge. Right now they are approximately 3' tall. They don’t seem to be filling in the space between each plant well but are growing thicker and taller each year. Should I trim these back severely to promote a wider spread of growth?”

Since you are in Zone 3 Catherine, the smaller-leaved variety may well not be totally hardy in your area--there are at least 20 different species of Cotoneaster shrubs (and that doesn’t include all the different cultivars of different species), about 16 of which would not be hardy with you in Zone 3. You should check with your nursery/garden centre as to just what species/cultivars you have.

As to the pruning of your taller-growing shrubs, they ought to have been cut back by 1/3 at the time of planting if you wish to develop them into a formal hedge. You could still do that early next spring, before any new growth appears, and just after the frost leaves the soil. Depending on what they look like, it might be better to cut them in half. Side shoots should also be cut back if bushiness is your object. A soluble or liquid fertilizer (even 20-20-20) would help as well applied soon after the clipping.

There are so many forms of Cotoneaster, as well as ways they can be grown (see accompanying photos), I am sorry I cannot help further.

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