All prohibited noxious and noxious weeds have to be plants that have been introduced to Alberta. None are native.
Prohibited noxious weeds are weeds that are not prevalent in the Alberta landscape. If they are growing in Alberta, they are only in a few locations in small enough numbers to be eradicated.
Noxious weeds are more prevalent than prohibited noxious. The chances of eradicating these weeds are slim so the aim is to contain them and stop them from spreading.
Originally, non-native plants were brought to this country by settlers who grew and depended on the plants for food. The plants escaped cultivation and became part of the landscape.
In the last 50 years, plants that have become a problem have either been introduced as an ornamental or hitched a ride on vehicles, animals, clothes or equipment. This being said, if there is a plant that has escaped the garden and is growing elsewhere, control it or it might be the next ornamental to join the list of weeds.
Are all the plants deemed prohibitive noxious a problem in Central Alberta? No. Growing requirements must be met before a plant multiplies so rapidly that it is hard to control. An example is the Russian olive, which is a problem in dry areas of the province but rarely seeds and can be hard to get established locally.
Seeds of impatiens glandulifera, also known as Himalayan balsam, poor man’s orchid, Himalayan impatiens and touch-me-not, has been passed between gardeners for 15 to 20 years. It is an easy-to-grow annual that starts easily from seed. Plants thrive as long as they receive an adequate amount of moisture and sunlight. The seeds can be sown outside in the spring and will grow quickly to maturity. Plants are easily removed by pulling. Seeds are the problem as one plant will produce a multitude of seed pods that explode and spread everywhere.
Himalayan balsam plants are easy to recognize. They have oblong leaves like other impatiens plants, hollow stems that will grow up to four feet (1.2 metres) and showy pink flowers.
Tribulus terrestris, puncturevine is not usually cultivated as an ornamental. It is a low-growing plant with opposite leaves and yellow flowers. The long tap root is hard to pull and the seed pod has two to three sharp spines that puncture objects to catch a ride to the next location. It will catch on clothing and make its way home from warmer climates during the winter months.
Hypericum perforatum, St. John’s wort, make a showy garden perennial. Unfortunately they can also make a showy weed that is toxic to domestic animals. Depending on the conditions the plants will grow up to three feet (90 cm) in height and are topped by attractive yellow flowers followed by rust-coloured seeds. The plants should not be sold in Alberta but seeds and plants can be found for sale outside the province. Don’t bring them home with you.
There are two types of tansy on the weed list. Ragwart senecio jacobea is classified as prohibited noxious. The small, yellow, daisy like flowers are clustered together along the stem and at the top. Plants will reach the height of three feet (90 cm).
Common tansy, tanacetum vulgare, is an escaped perennial that can be found in ditches and river valleys throughout Alberta. The rhizomatous roots spread quickly and are hard to eradicate once established.
Canadian thistle is so prevalent that it is on the list of plants to be contained. All other prickly thistles are prohibitive noxious. If you find a thistle that looks different, alert the nearest weed inspector.
For more information and pictures of plants on the Alberta weed list, visit the local government agricultural or horticultural department. Pictures and information can also be found at www.edmonton.ca/for-residents/weed-Identification-Book.pdf.
Linda Tomlinson is a horticulturalist who lives near Rocky Mountain House. She can be reached at firstname.lastname@example.org