Friday, July 17, 2009

Why you really shouldn't grow invasive plants

I just have to respond to Michele Owen's blog post, What's Invasive? Telling People What They Can't Plant In Their Yards, on Garden Rant. It's really disappointing that a professional garden writer is so uninformed about invasive plants, and is spreading misinformation through a widely-read blog.

Owens writes:

A civilized society makes the fewest rules possible. If it's not hurting you, it's fine for me to do it.

I totally agree, and I think most people would. The problem is, invasive plants, by definition, hurt others—invasive species are second only to outright destruction in causing habitat loss. Habitat loss not only harms wild animals who are driven extinct, it also harms people as we lose all the benefits of well-functioning ecosystems:

  • purification of air and water
  • mitigation of droughts and floods
  • generation and preservation of soils and renewal of their fertility
  • detoxification and decomposition of wastes
  • pollination of crops and natural vegetation
  • dispersal of seeds
  • cycling and movement of nutrients
  • control of the vast majority of potential agricultural pests
  • maintenance of biodiversity
  • protection of coastal shores from erosion by waves
  • protection from the sun's harmful ultraviolet rays
  • partial stabilization of climate
  • moderation of weather extremes and their impacts
  • provision of aesthetic beauty and intellectual stimulation that lift the human spirit
Source: Biodiversity and Human Health: Benefits of Ecosystem Services

(For more information on invasive plants, native plants, and their impact on ecosystems and all life on earth, I highly recommend Bringing Nature Home by Douglas W. Tallamy (Portland, OR: Timber Press, 2009).)

Owens' response is that naturalized invasives, like the Hemerocalis fulva (orange daylily, lis d'un jour fauve) which grows by the roadside, are pretty. It's true, some invasives, like H. fulva, are pretty. But why grow them, destroying habitat, when there are so many other plants which are pretty and ecologically benign?

Owens rhetorically asks,

Should our world therefore be nothing but weeds and overbred, super-fussy garden plants?

Of course not! But it's just wrong to assume that the only alternatives to invasive plants are "weeds" and fussy plants. Many native plants are as beautiful as the invasives she admires, if not more so. Here in Toronto, our showy natives include:

There are too many plants native to Toronto to list here (the index to my 25 posts listing them is here), and the same is true for any part of the world where plants grow.

In addition, there are many well-behaved non-natives that are not "overbred" and "super-fussy". Indeed, if she had looked more closely at the list of invasives that she complained about, she would see that it's only so long because it covers all of the United States, a large country with many different ecosystems which are vulnerable to many different invasives. Yes, Alcea rosea (hollyhock) is on the list, but is only a problem in California, so New Yorkers like Owens can still grow it in good conscience. (Click each plant name on the list to see where it is invasive in the U.S.) Wherever you live, there are many non-natives which will grow well and not invade local ecosystems. (Although, read Bringing Nature Home to learn why you should grow lots of natives.)

(Owens also wonders why Aruncus dioicus (goatsbeard, barbe de bouc), which grows freely in her garden, is not on the invasive list. The answer is simple: because it is a native plant! It's a contributing member of the ecosystem in New York where Owens lives and elsewhere in North America.)

Owens attributes concerns about invasive plants due to "paranoia and lack of trust". If only. Extensive experience has shown that certain plants in certain areas are extremely harmful. It doesn't make sense to ignore decades of scientific research just because a gardener thinks some invasive plant is pretty.

1 comment:

  1. Rosemary, You make some excellent points and should post a link to your response on the Garden Rant site.


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