Documents: Hot Horticulture Issues:

Bougainvillea & Invasive Plants

How to propagate a Bougainvillea (if you must!); and a comment about so-called invasive plants!
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


December 2, 2007

Above: Just some of the colours of Bougainvillea available. Below: goutweed helps set off the Grevillea ‘Cranberry Gem’ evergreen shrub and an azalea in my own garden, followed by a close-up of Lamium galeobdolon (note the insect invader!), and two shots of Norway maples, the lower one being the columnar form which makes a good boulevard tree. Author photos.



Jim Lenoir wrote from an entirely different climate on November 19 with this question: “I retired in Mazatlan Mexico and recently I purchased some property and want to plant about fifty bougainvillea plants. Could you give me any help on growing them from cuttings? Any help would be appreciated. Thank you”

Bougainvillea is apparently named after a Canadian, Louis de Bougainville, who was an explorer, mathematician and lawyer back in the late 1700s. There seem to be conflicting reports as to whether it was discovered in South America in 1790 (by Louis de Bougainville), or slightly earlier in 1767, but I guess we won’t argue over a mere 23 years when it happened that long ago!

Most growers agree that stem cuttings should be taken in spring and propagated in a 50/50 peat and sand mix with basal heating if possible. Obviously humidity is also necessary. There are some who say that tip cuttings are best, while others say woody half-ripe mid-stem cuttings are as good or better. These should be taken in the period of April to June and should be at least 15 cm long, and can be up to double that.

Others have propagated Bougainvillea using air-layers and even root cuttings. Finally, some growers actually claim to be able to grow Bougainvillea from seed, and you may be able to find some offered for sale. The plants produce precious little (if any) seed however, and I would not waste too much time looking for it. And I should also add, that some grow-ers say it is much easier to purchase new small plants rather than trying to propagate even using the cuttings method!

* * *

The topic of invasive plants and specifically the sale of them in nurseries and garden centres has come up again, in more than one publication. Folks say that garden centres should not sell, or even stronger, should not be allowed to sell invasive plants. The question is whose definition of “invasive” is being used. Perhaps one of the best examples is the variegated ground elder or as it is more commonly called goutweed, or bishop weed and even snow-on-the--mountain. Regardless of what name you use, it is (botanically) Aegopodium podagraria ‘Variegatum’, and it very definitely is invasive. Many garden centres where it is sold do label it well as “very invasive” but still others do not.

Regardless, I certainly do not think it should be banned from sale, as it is a good groundcover plant, used under the right conditions. That usually means restraining it in a container or containers of some type that will prevent the roots and running stems from spreading high and wide in the garden. However, planting it in this way will not stop the seeds from spreading the plant to other nearby parts of the garden. The only way to prevent that aspect of the spreading is to shear off the seed heads (which are quite pretty) before the seeds are actually produced.

There are, of course, many other “invasive” plants, ranging from what some refer to as “noxious weeds” to the oft’ planted Norway maple (Acer platanoides) which I know many of my readers/listeners will argue with me about as to whether it is a scourge, or possibly just a slight nuisance. I know the shallow lateral roots can be a nuisance in a surrounding lawn, and I know the samaras (keys or seeds) are abundant and lead to ever so many tiny seedlings in the gar-den. But, it’s a nice mid-sized tree that grows almost anywhere in the milder parts of Ontario, for example. And, as just one example, I can show you streets of smaller homes with a Norway maple on each lawn where they still have good lawns within the Greater Toronto Area. Not all are great but many are not as bad as often reported by the naysayers!

What each one of us considers an invasive plant or a noxious weed depends entirely on many factors including your particular climate, your home region and your view on having a diversity of species. It certainly is a hotly debated topic within the horticultural industry. Here are three examples of how the vision of just what is invasive and what is not changes from area to area. In England they are actually bulldozing square kilometres of rhododendrons that have become a nuisance--weeds in that particular environment. In South Africa the common Lantana--which we very much value here as a distinctive, long-flowering tropical shrub--is on the noxious weed list and is not allowed to be planted and is routinely routed out by municipalities from natural vegetation areas. In Australia it is the same thing with Pampas grass--it’s absolutely a no-no. Australian gardeners visiting here are surprised that we allow it and that it does not cause us problems.

Who would even consider arguing that no one in the rest of the world should be allowed to grow them?

Many plants such as Lamium are annoying garden weeds if planted in the wrong place but useful in the right place (such as under some dense trees near our front gate where they even take being stepped on), and they are not a threat to native plant communities. The exact same characteristics that make a plant a good groundcover make it a disaster if planted in a mixed bed (or thrown on top of a compost pile). Words like “vigorous,” “fast-growing,” or “easy to grow” on the labels should be a clue! [And, the presence of a plant species or variety at every plant sale you visit in your own town or city should set off warning signals. As nice as most gardeners are, they are seldom as generous with varieties that aren’t overrunning their gardens!]
 

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