On The Proposed (And Actual) Banning
Of Purple Loosestrife!
loosestrife growing in Tommy Thompson Park on Toronto's waterfront.
Seven years ago this August, I
returned from a three week trip across Canada, from Osoyoos, British
Columbia, to Pasadena, Newfoundland. We travelled by small plane, large
plane, fast train, slow train, and car. I was head of a judging team for
Communities in Bloom in its first year of operation, and while the trip
was to judge competing municipalities in eight provinces, we also had a
great opportunity to observe the country horticulturally in general.
In every province (except Newfoundland, where there is very little),
purple loosestrife (Lythrum salicaria) was at its best! Media
reports have once again been condemning the plant, a common herbaceous
garden perennial that it is claimed could well, in just a few more years,
cause the demise of the few wetlands that Canada has left. The plant grows
equally well in sun or part shade, but definitely prefers moist
conditions. Its tall spikes of carmine-pink flowers are displayed from
mid-June to late August, and it’s generally a very good perennial for
garden use, particularly if you have a pond or damp area.
However, biologists and naturalists are calling for a government ban on
the sale and propagation of the plant which they say, as a non-native, has
no natural predators and is quickly taking over our already-too-few
wetlands, and causing them to fill in.
I must point out that to call for an outright ban is not only a gigantic
over-reaction, but also it simply will not work. It's decades ago now that
the common barberry (Berberis vulgaris) plant was banned because it
was said to be an alternate host to wheat rust disease. That ban has been
anything but effective! You can see common barberry growing wild and in
abundance still, and, what about other similarly introduced non-native
plants. Common tansy (Tanacetum vulgare) is in full yellow bloom in
August in many areas, and no one seems to be suggesting it be banned.
Viper's bugloss or blue thistle (Echium vulgare) is spectacular
many years. It is widely distributed and came from Europe, but there is no
call for it to be banned, and it too prefers moist areas.
Purple loosestrife is a beautiful garden plant with a long blooming
period, insect and disease resistance, and for most gardeners is safe to
plant from a wetland point-of-view. Virtually all of the plants sold in
Canada are cultivars developed by our own Agriculture Canada at their
famous research station in Morden, Manitoba.
In response to continuing negative publicity, mostly from writers who just
follow what others be-fore them have written, I decided to do a little
investigation into the whole subject. I found that the possibility of
purple loosestrife taking over other common wetland border plants such as
cat-tails and natives such as willows is highly unlikely.
My late colleague Fred Dale had a farm pond edged with natives. He pointed
out that naturally introduced purple loosestrife had been pushed right out
by the native willows and cedars, and cattails. Just what is behind the
campaign to ban this beautiful, useful plant? It is a well-known fact that
the anglers & hunters are the main organization pushing for a ban.
These people don't like loosestrife around their fly-fishing ponds because
they cannot fish from the edge due to its rapidly expanding growth. They
would also, by the way, like to see cattails reduced to about 50 percent
of their present numbers.
Will it in fact be responsible for the complete demise of all of our
wetlands, as is promoted by the self-interest groups? Do you realize
wetlands remain in existence for only a period of time--regardless of
so-called predators such as loosestrife? Our individual existence is but a
tiny fraction of the life of the planet. For us to say that wetlands are
being destroyed entirely during our lifetime is rather self-serving. In
fact, over the next 100 years, virtually all the wetlands we now know will
cease to exist, and many new such lands will be formed. Observers of the
natural progression of the planet's landform confirm this.
The real reason certain groups see purple loosestrife as a threat is that
it threatens their sports--angling and hunting, and they have been
successful in convincing other conservation groups that the plant is
actually a threat to wetlands themselves. According to a past president of
the Toronto Field Naturalists, the Ontario Federation of Naturalists have
been receiving considerable funding from Ducks Unlimited and they have
joined with the anglers & hunters in trying to have loosestrife
Tom Thomson, a horticulturist acquaintance of mine, has suggested that we
form a new organization to oppose hunting--particularly the “pouring”
of lead from shot into our rivers and lakes. Naturally, the symbol for
this new organization would be purple loosestrife!
I have been defending this plant, and reminding gardeners and others of
its good points (excellent for bees and honey making, colourful, does well
in a variety of conditions, insect and disease resistant, and has a long
blooming period), for over a decade now. In that time I’ve been
subjected to criticism and tongue-lashings from government officials,
do-gooder (so-called) environmentalists, conservationists,
preservationists and poor lowly gardeners who don’t know whom to
During a spring garden show two years ago I had at least a dozen people
comment to me about how harsh some readers of Plant & Garden had been
on my comments about purple loosestrife. I replied that I was used to such
reactions. The lobby against the poor plant is large and well funded by
anglers and hunters, and now to a great extent by government officials,
many of whom have been duped into spending our tax dollars on schemes that
will help “the cause.”
Those who are genuinely concerned about our plant environment, such as
Helen Juhola, newsletter editor and past president of the Toronto Field
Naturalists, have thoroughly investigated “alien species” and don’t
see them in the same light as many of the anti-alien-plant people. In many
cases those concerned about purple loosestrife have only themselves or
their predecessors to blame because land has been disturbed and that’s
where “the purple demon” is able to come in and take over.
Those condemning the plant might well check with competent researchers
such as Dr. Spencer Barrett of the University of Toronto’s botany
department. Dr. Barrett’s Ph.D. dissertation was on invasive alien
species. He and his colleagues in that field dare anyone to show a
natural, undisturbed pristine environment where purple loosestrife has
invaded. He also points out the following. 1) The plant, though a major
nuisance, is not causing any great economic loss (except maybe to the
anglers and hunters!). 2) There is no data showing that it causes any loss
of diversity of species. 3) It does not affect ecosystem health because
most of the ecosystems are al-ready disturbed.
It is also interesting to note that University of Guelph zoology
department professor Ted Knuds a few years ago released a paper discussing
the pros and cons; and it concludes that the threats attributed to purple
loosestrife are largely exaggerated, a point I have been making for a full
Further, I understand that the totally inept and misdirected research
project at the University of Guelph that introduced three supposed
bio-control insects--two that attacked the foliage, and one the roots--is
finally ending because the funding has been cut. (Do we not remember
rabbits in Australia and starlings here?) Though the funding has been cut
we may well yet face a problem from one or two of these introduced species
attacking other unique garden plants!
The negative campaign by so-called environmentalists who would see
us--every one of us--going out and ruthlessly pulling out all plants along
waterways, roadways and fields, as well as not planting (or not even being
allowed to plant) it in our gardens, is actually
The most interesting newer data comes from two studies done at the
University of Guelph and completed in late 1997. Each was published in a
professional journal, and I recently spent a half-day reviewing the
manuscripts in detail. I can tell you at the outset, they are not good
news for the do-gooder so-called environmentalists!
The first released appeared in the journal Biodiversity and Conservation
7, issued in September 1998. It’s entitled “The implications of
accepting untested hypotheses: a review of the effects of purple
loosestrife in North America.” Authors Heather A. Hager and Karen D.
McCoy were then at the University of Guelph department of zoology; Heather
is now at the University of Regina, department of biology and Karen at l’Université
Pierre et Marie Curie, laboratoire d’écologie, Paris, France.
The abstract of their paper reads: “The acceptance of poorly tested
hypotheses has adverse scientific consequences, and may have adverse
ecological and social consequences. The hypothesis that purple loosestrife
has deleterious effects on North American wetlands is an example. We
traced the history of purple loosestrife and its control in North America
and found little scientific evidence consistent with the hypothesis that
purple loosestrife has deleterious effects. The most commonly cited study
of the effects of purple loosestrife on native flora and fauna produced
inconclusive results. The general acceptance of this hypothesis, however,
has resulted in the introduction of non-indigenous insects for biological
“Efforts to control purple loosestrife may be misplaced and may have
long-term ecological consequences if loosestrife does not have the impact
it is believed to have. The acceptance of this hypothesis using scientific
justifications may affect future scientific credibility. Careful
evaluation of the precautionary principle is necessary when considering
the control of non-indigenous organisms.”
If you have any doubt about this, I would encourage you to read the entire
The second study is perhaps even more interesting. It is entitled “Relationship
between the abundance of purple loosestrife and (other) plant species
richness along the Bar River, Canada.” Its authors are Michael A.
Treberg and Brian C. Husband then both of the department of botany,
University of Guelph. Michael is now at the University of British
Columbia, department of geography.
The study was carried out along a 2.5 km section of the Bar River, about
30 km east of Sault Ste. Marie, Ontario. This river is described as slow
moving and its banks vary from gentle slopes to steep banks of up to two
metres in height. The steep banks often collapse into the river, providing
new areas for plant colonization. The soil is heavy clay with very little
organic matter near the water’s edge and with increasing organic matter
content further up the bank.
The authors point out that they chose the site for a number of reasons,
not the least of which were: 1) loosestrife has colonized the river for
about 12 years and thus sufficient time has likely passed for the impacts
of loosestrife invasion to develop; and 2) the river offers a wide range
of densities of purple loosestrife.
Their paper appeared in its entirety in the journal Wetlands, published by
The Society of Wetland Scientists (you certainly couldn’t ask for more
credibility on this topic than this group!) in March 1999.
Here’s their abstract. “Purple loosestrife is a perennial herbaceous
plant that was introduced in the 1800s into North America. Its
geographical expansion has generated much concern, in part because its
spread may lead to a reduction in the diversity of plant species in
wetlands. We tested this hypothesis by examining the association between
the abundance of loosestrife and vascular plant species richness in 41 2m2
plots along the Bar River. No significant differences in mean species
richness were found between plots with and without loosestrife. For those
plots containing loosestrife species richness was not related to the
percentage cover of loosestrife. Furthermore, there were no significant
differences in the number of introduced plant species be-tween plots with
and without loosestrife, nor were there differences with increasing
percent cover of loosestrife. [Some] plant species such as [three] Scirpus
species were more likely to be found in plots with loosestrife than
without. However, no plant species were significantly more likely to be
found in plots without loosestrife than with it.
“Collectively, these results provide no support for the hypothesis that
the number of species in wetlands is decreasing in association with the
invasion of loosestrife in Ontario.”
Even before they began this significant study, the authors noted that in
issue 19 of the journal Environmental Management, professor M.G. Anderson
had found, during his review of literature (in 1995), “that studies of
competition between loosestrife and other plants are few, but of those
conducted in the field, some have shown that loosestrife seedlings cannot
compete with native species and that stands of loosestrife were frequently
invaded by native species.
“These results are inconclusive and suggest that the impact of
loosestrife in North America may be more complex than was originally
This latter observation: stands of loosestrife being invaded by native
species is exactly what was observed back almost two decades ago by
colleague Fred Dale, gardening columnist for the Toronto Star. Fred’s
observations were based on his personal experience along the stream and
pond on his own rural farm. If only Fred were alive now to see his and my
comments of the time being confirmed by “ivory tower academics!”
Art C. Drysdale, Horticulturist.