Invasive Plant Species – in honor of National Invasive Species Week

green ferny foliage with clusters of small yellow button like flowers

Common Tansy

They are insidious!  They start out as a few pleasing plants and you think  “oh they aren’t so bad” and you leave them be.  Next thing you know there are a few more, and eventually lots of them.  By the time you’ve decided it was a mistake not to get rid of those plants, it’s a difficult (if not impossible) job to eradicate them.   Invasive plant species are often attractive plants.  Many have been intentionally planted as ornamental species in gardens and landscapes by people who had no idea that they would be problematic.

According to the USDA invasive species are:

1) non-native (or alien) to the ecosystem under consideration and

2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

ssingle lavender pink flower with delicate, wispy petals and blue-green sparse foliage

Spotted Knapweed

Plants may be well behaved and non-invasive in one area and considerably misbehaved and very invasive when imported (usually by humans) to another area.  Invasive species threaten native plant populations and cost millions of dollars annually to control.

In our area Spotted Knapweed, Leafy Spurge, Dalmation Toadflax, Cheatgrass, Common Tansy, Oxeye Daisy, Bindweed and Yellow Flag Iris are particularly problematic.  Some, like knapweed, produce alleleopathic chemicals that actually inhibit other species from growing next to them.  Others, like Leafy Spurge, have extensive, fast-growing root systems that make erradication nearly impossible.  It is important to deal with invasive species BEFORE they become established.  If you see small plants, get rid of them!  Avoid disturbing the soil unnecessarily which allows weed seeds to germinate.  And don’t let them go to seed – cut off flowers whenever possible.

5 White morning glory type flowers with green vines


Check out the Montana Weed Control Association’s website: for more information on weed identification and management.