The secret life of common garden plants
Volunteers at James Island (Photo by NCC)
May 16 to 23 was National Invasive Species Awareness Week. In the spirit of growing awareness and offering solutions, the Nature Conservancy of Canada's (NCC's) stewardship coordinators in BC are sharing some notable troublesome invasive plants that they manage on our conservation lands. They are calling attention to some plants that may surprise some home gardeners, as these invasive species lead double lives as common ornamental garden plants.
Steven Godfrey, BC (Photo courtesy S. Godfrey/NCC staff)
Steven Godfrey is our West Coast stewardship coordinator. He is most concerned about spread of invasive species in Garry oak ecosystems, which support very high numbers of species at risk. Invasive plants can outcompete native species, putting even more pressure on at-risk plants and animals in the habitats they need to survive. Steve believes a little bit of research goes a long way: “There are tons of great resources out there like the Invasive Species Council of BC's website. People have worked hard to figure out the best approach to dealing with just about every invader, and it's better to learn from them, rather than finding things out the hard way!”
Common coastal invasives
Saint John's wort (Photo by Matthew T. Rader, Wikimedia Commons)
St. John's wort
This common medicinal plant has numerous bright yellow flowers with five separate petals arranged in a flat-topped terminal cluster. The leaves are oval shaped with prominent veins and several tiny, translucent black edged glands that give them a perforated appearance. St. John's wort impedes the growth and regeneration of native forbs, shrubs and trees by competing for nutrients and space. Populations of this plant can form dense colonies with extensive creeping rhizomes, growing to one metre tall. Toxic to animals, this plant can reduce species diversity where they establish.
Butterfly bush (Photo by Dave Whitinger, Wikimedia Commons)
Also known as buddleias, this fast-growing deciduous shrub often gets mistaken as a “good guy” because it attracts pollinators. But this actually leads to reduced pollination for native species. Don't be fooled by its long panicles of colourful flowers — once established the butterfly bush displaces native vegetation, supplants other plants as a nectar source and outcompetes native vegetation.
Danielle Cross, Southern Interior stewardship coordinator (Photo by Danielle Cross/NCC staff)
In the Southern Interior, Danielle Cross tackles invasive species in NCC's many grassland conversation areas. The majority of her invasive species work concerns plants rather than animals, though bullfrogs are a growing problem in her region, and across BC. Her advice for controlling invasive plants is to “be conscious of not tracking weed seeds into and out of areas you visit, clean your boots before and after hiking, clean your bikes or other recreational gear, do not drive off roads or trails, keep pets on leash and, remove any seeds, burs, vegetation before travelling back home. The same applies for trips with horses."
Common grassland invasives
Purple loosestrife (Photo by Liz West, Wikimedia Commons)
Native to Europe and Asia, this wetland plant has pink-purple flowers and can grow up to one-and-a-half metres in height. Purple Loosestrife can be found in wet meadows, river floodplains and damp roadsides. It has even popped up on Osoyoos Oxbows and is a problem across riparian areas across much of BC. Still used in flower gardens and sold in nurseries, this plant aggressively degrades and lowers the value of a wetland for use by wildlife, clogs irrigation and drainage ditches and chokes out native vegetation.
Common tansy (Photo by NCC)
Native to Europe, common tansy was introduced to North America in the 1600s as a horticultural and medicinal plant. It has yellow, button-like flowers and grows up to 1.5 metres high. The seeds of this plant spread very easily by animals and vehicles. In addition to outcompeting native plants, common tansy produces a toxic compound that can impact cattle and wildlife when ingested.
Kate MacKenzie (Photo courtesy K. MacKenzie/NCC staff)
Kate MacKenzie is NCC's Canadian Rockies stewardship coordinator, where she manages both grassland and forested sites. She encourages people to check out the East Kootenay Invasive Species Council (EKISC) website because they have a lot of resources for landowners. For example, EKISC runs public outreach events, community weed pull events and training courses specifically aimed at community volunteers. They have even helped to host a community weed pull on NCC's Cherry Meadows conservation area!
Common East Kootenay invasives
Oxeye daisy (Photo by Gabelstaplerfahrer, Wikimedia Commons)
Also called "moon daisy" or "moonpenny," the oxeye daisy has flowers with yellow centres surrounded by white petals. A popular garden plant, its seeds still show up in wildflower seed mixes despite being highly invasive.
Common toadflax (Photo by Ryan Hodnett, Wikimedia Commons)
These herbaceous perennials with yellow snapdragon-like flowers and pale green leaves can form horizontal roots as long as 3.7 metres, allowing for substantial growth. Infestations of dalmatian toadflax can withstand cooler weather and reduce forage production and quality for livestock. This plant, the seeds of which are unfortunately still sold in wildflower seed mixes, is toxic to animals.
What you can do
Thankfully there are a many great native plant options that we can grow in our gardens instead. You can learn more about what to grow, and what to avoid or remove, in this comprehensive publication from the Invasive Species Council of BC.