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Cherry Laurel & Earthworms

Howard Dunington Grubb’s favourite plant--who sells it now; and, now it is revealed earthworms may be harmful to naturalized plantings!
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


August 31, 2008


Above, two shots of what is likely the hardiest cultivar of Cherry Laurel--Prunus laurocerasus ‘Schipkaensis’. The top one is courtesy of David Maguire, www.maguirelandscapes.com , and the second one by Michael Dirr. Below, a shot of one famous red wiggler, now suspected of being a negative to native plant areas.

A week ago Monday, Bob McKenzie wrote with a question about one of my favourite plants--Cherry Laurel (Prunus laurocerasus). It was a favourite of the late founder of Sheridan Nurseries, Howard Burlingham Dunington Grubb, and I guess I inherited my like of the broadleaf evergreen shrub from him, a way back in the early 60s! [Incidentally, you can read more about ‘Grubby’ as we affectionately called him, on my own Website at http://www.artdrysdale.com/howardgrubb.html .

Here is the question: “I have heard that the Cherry Laurel (Prunus laurocerasus Schipkaensis) is a very good evergreen to form a hedge. A few questions for you regarding this tree. One, we would planting at our cottage on Balsam Lake, which is just north of Lindsay, Ont., so would this tree be able to handle a good Canadian winter? Two, is this tree readily available for purchase in southern Ontario? Three, about how far apart would you recommend planting them? We have a stretch of about 15 to 20 feet on a property line we want to create a hedge for. How many trees would you recommend purchasing? Thank you.”

My quick answer to your first two questions is “No!” And I guess that makes the third one redundant, doesn’t it.

First, regarding my acquaintance with the plant, it began in 1962 when I joined Sheridan Nurseries as their horticulturist. As mentioned, it was the founder’s (Howard Dunington Grubb’s) favourite broadleaved evergreen. The folks at Sheridan grew it, but only used it in special landscape jobs designed by Mr. Grubb. Only occasionally did it appear in the company’s garden centres, although we did list it in the catalogues in the 60s. It grew reasonably well in the Oakville area and that is where the nurseries were in those days. As most of the growing activities transferred to Glen Williams (near Georgetown) generally we found it did not do nearly as well up there.

I kind of lost track of it after I left Sheridan in 1969, and not until I moved into my Nesbitt Drive home in the Bayview/Moore area of the city in 1986, did I have contact with Cherry Laurel again. I found one, fairly large, growing on nearby Douglas Crescent (#48) and talked to Neda Leipen, the owner of the house. It turned out she had her house landscaped by Sheridan “a way back when” which made sense, knowing what I knew from the 60s. One winter while we were there (perhaps 1987-88) the ladies’ Cherry Laurel was killed almost to the ground, but I urged her to leave it and sure enough it rebounded, and in two or three years was back up to a height of almost two metres.

The specific cultivar to which you refer, ‘Schipkaensis’, is said by many (including Michael Dirr, the expert’s expert!) to be the hardiest variety, and is also said to grow in such locations as Chicago. That would indicate it should certainly grow in southern Ontario, but that may not include your area which is likely Canadian Plant Hardiness Zone Map (1967) zone 5a or possibly even 4b. Just how much natural cover from other larger trees (especially evergreens) your property has would determine the actual hardiness. Snow cover as well, would be a major factor, especially in the first two or three years.

The only answer to all this is to try one, and therein is the problem! While they may be available from nurseries out here in the West (e.g. Hutchinson Nursery Sales in Aldergrove, where Gerry Hutchinson is an old acquaintance of mine, who I have contacted with a question about this plant), I think it would be far better to try and obtain some or one from an eastern source. Unfortunately, I am not able to make a specific recommendation. However, you might wish to ask Jim Lounsbery at Vineland Nurseries in Vineland Station Ontario ( www.vinelandnurseries.com or 905-562-4836), or John Vanderkruk at Hortico in Waterdown ( www.hortico.com or 905-689-6984).

If you do find some, I would rely on the advice of the nursery as to how far apart to plant them. Certainly that always depends on the size and business of the actual plants. I would think though that you could count on about 45 to 60 cm apart.

* * *

This week, for some reason, I was catching up on some reading on which I had fallen behind. I came across an item in the November issue of the Toronto Field Naturalists Newsletter (#543), entitled “Ecology Tidbits” which author Allan Greenbaum has written previously on various subjects. This one was about earthworms, which it seems to me every gardener (almost) has been convinced are simply the best critters to have in the garden. Many writers promote (and sell) red wigglers (Lumbricus rubellus) to gardeners to help loosen up clay soils. And, generally the observation of a good quantity of earth-worms in any garden soil is a good sign!

But maybe not for all plants and soils! “There is increasing evidence that earthworms can have a negative impact on biodiversity in natural [plant] communities. (See: http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/Lumbricus_rubellus.html .)

“The most recent evidence comes from a study by researchers at the University of Minnesota who compared the groundcover in sugar maple/yellow birch/basswood forests on either side of the earthworm invasion ‘front’ running through northern Minnesota.

“There are several species of European earthworm on the loose in the Minnesota woods and, because they have different life-styles and feeding strategies (e.g., some species chomp on litter on the surface, others stay deeper in the soil), they have different ecological effects, so the number of species present can be at least as important as the total number of worms.

“It turns out that the red wiggler is particularly bad news for native plants. While worm-free sites had a rich ground cover of maple seedlings, blue cohosh (Caulophyllum thalictroides), large bellflower, sweet cicely, trilliums, wild ginger and Solomon’s seal, the sites with the most red wigglers were dominated by the sedge Carex pensylvanica and Jack-in-the-pulpit. Plants that reproduce vegetatively (like the sedge and Jack-in-the-pulpit), or that produce substances worms don’t like (such as wild leek and Jack-in-the-pulpit again) were affected the least, and plants that propagate by means of big seeds were affected the most. Previous research in Minnesota has already implicated the spread of the wigglers in the decline of a rare species of grapefern.

“It is not entirely clear why the earthworms affect plant communities the way they do, but they have a dramatic effect on the forest floor, thinning and mixing the duff layer with the underlying mineral soil and changing the fungus populations. Since most native plants depend on symbiotic mycorrhizal relationships with fungus, this latter effect could play an important role.

“In northern Minnesota, the worms were commonest around roads and fishing lodges, suggesting that they were mainly introduced as bait and perhaps in soil clinging to tire treads. In settled areas like Toronto, of course, the main avenue of introduction would be horticultural (via soil), and the worms have been around for a couple of hundred years. Are our forests less vulnerable to the effects of these worms? Have they adapted to their presence? Or are even the richest forest communities we encounter in our region impoverished as compared to their pre-wiggler state?”

Thanks to Allan Greenbaum and the Toronto Field Naturalists for this item.

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