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American Society of Landscape Architects
Northern California Chapter

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Growing Crazy: An Intro to Invasive Plants

Growing Crazy: An Intro to Invasive Plants

by Greg Richardson

Update(d) is greatly pleased to launch a new ASLA-NCC column: “Don’t Grow Crazy”. The series will be produced in partnership with PlantRight, a nonprofit project that works with horticulturalists throughout California to promote the use of noninvasive plants. Articles will focus on the intersection of invasive plants and horticulture to keep our community ahead of relevant sustainable landscaping trends.

But first… What does “invasive” mean to you?
Let’s make sure we’re all talking about the same thing. While pesky weeds grow in our landscapes (against our best intentions), this column will focus on the plants we intentionally select that become damaging weeds in natural areas.

Are all non-native plants invasive? Of course not. Here are 3 ways to help you differentiate between various types of exotic (aka non-native) plants:

  • Naturalized plants are successful at adapting and reproducing in a new region, but don’t necessarily spread.
  • Weeds are able to spread in agricultural, urban or other areas but only with irrigation, tillage or added nutrients.
  • Invasive plants can thrive with no additional water, nutrients or tillage and spread in a fashion that causes harm.

In general, 10% of the non-native species that enter a new ecosystem will survive, and of those survivors a further 10% (or just 1% of the original number) will become invasive.

What’s the big deal?
While the majority of ornamental plants do not spread beyond where they are planted, those that do can cause significant damage. They can crowd out existing plants and wildlife, increase fire severity, reduce agricultural yields, decrease land value, impact water supplies, and degrade recreational opportunities, among other things. This affects waterways, biodiversity, soil composition, and creates a financial burden on taxpayers and others trying to contain invasions. In California, over $80 million and countless hours of painstaking labor is spent each year trying to manage invasive plants, yet in many areas they continue to spread.

Despite their myriad costly impacts, many invasive plants continue to be sold as ornamentals today. Examples include Green fountain grass (Pennisetum setaceum), periwinkle (Vinca major), Mexican feather grass (Nassella tenuissima) and pampas grass (Cortaderia selloana).

Stipa tenuissima lined up and ready for shipment from the nursery!

Solutions
Fortunately, basic decisions can make a big difference as it is far more cost-effective to prevent the introduction of invasive species than to manage those that have already escaped into the wild.

The first step to curbing the spread of invasive ornamental plants is awareness, and through this series and other educational opportunities, PlantRight will provide ASLA-NCC members with training opportunities and resources to stay on top of this important topic.

“This is really about using better plants” explains Scott Lewis, ASLA. “By choosing non-invasive plants that stay where they are planted, we are not only being good stewards of the environment but creating lower-maintenance landscapes, which saves labor and reduces long-term costs for clients.”

Because California is home to a wide range of climates and eco-regions, plants that may be invasive in one area (e.g. forests) may not be of concern in another (deserts). Since 2005, PlantRight has been working across the horticultural supply chain in California to encourage action on this issue in a regional, science-based and voluntary fashion. See PlantRight’s list (www.plantright.org/map) for a variety of noninvasive alternatives to consider using in your area.

What’s next in “Don’t Grow Crazy:…

Future articles in this series will feature more specific topics, like: the pros and cons of sterility; the art of choosing noninvasive alternatives; predicting the risk of emerging ornamental invasives; relevant regulations for landscape professionals; and bigger questions like “should we just let nature run its course”?

If there are topics you’d like us to write about, let us know at PlantRight@SusCon.org . Stay tuned!

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