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Weed of the Week: Yellow Flag-Iris

Many wetlands, ponds, lakes, and backyard gardens of southern British Columbia are rimmed with a beautiful water-loving plant called yellow flag-iris (Iris pseudacorus). Seemingly harmless and eye-catching at first glance, this plant poses a significant threat to surrounding ecosystems.

Sword-shaped leaves and showy yellow flowers with three sepals distinguish yellow flag-iris, making it a gardening favourite world-wide. Native to Europe, the British Isles, North Africa and the Mediterranean region, yellow flag-iris is considered invasive in BC.

Invasive plants grow rapidly and spread quickly, causing damage to the environment, economy and our health. They are also the second greatest threat to biodiversity after habitat loss, according to the International Union for Conservation of Nature (IUCN).

Yellow flag-iris forms dense patches that displace native plants, alter wildlife habitat and restrict water flow in irrigation canals and flood control ditches. Currently this plant is found in BC’s southern interior, and has quickly spread throughout the Okanagan valley, lower Similkameen valley, Christina Lake and other isolated sites in the West Kootenays.

Yellow flag-iris reproduces quickly through seed dispersal and horizontal root systems, creating thickets in the water like cattails (Typha spp.), and reaching 1.5 metres in height. Several hundred flowering plants may be connected rhizomatously under the water, and fragments can form new plants when they break off and drift downstream.

Reproducing quickly on its own, this invasive plant is helped along exponentially by gardeners. Yellow flag-iris is widely sold in nurseries and on the Internet for wet areas and well-mulched soil. The popularity of the plant in the market is making efforts to contain new infestations difficult. A total of 75% of today's invasive plants were intentionally introduced as ornamentals and cost Canadians millions of dollars each year in lost productivity and increased management costs.

Help your community protect local resources by managing invasive plants. There are hundreds of native aquatic plants that are critically important to parts of a lake or river ecosystem, and alternatives are available to replace this attractive invasive in your backyard.

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