Noxious Weeds in Your Alberta Yard: How to Spot & Remove Them

What “noxious” actually means in Alberta

Alberta’s Weed Control Act divides problem plants into two legal categories:

• Prohibited Noxious — the worst-of-the-worst. These plants are not yet widely established in Alberta, and the law requires them to be destroyed. Every plant, every time. Examples: giant hogweed, yellow starthistle, saltcedar, purple loosestrife.
• Noxious — already established in Alberta and difficult to eradicate entirely. The law requires landowners to control them — meaning prevent spread, stop seed production, and reduce the population. Examples: Canada thistle, leafy spurge, common tansy, common mullein, oxeye daisy, scentless chamomile, toadflax.

Municipalities can also add plants to their local noxious list. Your city or county’s Agricultural Fieldman (in rural areas) or Parks department (in cities) is the authority on what’s regulated where you live.

Why it matters

Invasive plants don’t just outcompete native wildflowers for space. They change soil chemistry, reduce wildlife forage, poison livestock, clog waterways, and cost Alberta municipalities tens of millions of dollars a year to manage. On a smaller scale, a few untreated noxious weeds in your yard can seed thousands of square metres around you in a single summer.

Getting them out of your yard is one of the most high-impact things you can do for local ecology — and it’s legally expected.

Common noxious weeds you’ll actually find in an Alberta yard

The full Alberta noxious list has around 75 species. Most homeowners will only encounter a handful. Here are the ones you’re most likely to see:

Canada Thistle (Cirsium arvense)

Spiny-leaved perennial with pink-purple flower heads in clusters. Spreads underground by aggressive rhizomes — pulling a stem rarely kills the plant. Small root fragments regrow. One of Alberta’s most widespread and stubborn weeds. See our Canada Thistle plant page for full profile and control details.

Leafy Spurge (Euphorbia esula)

A knee-high perennial with narrow blue-green leaves and distinctive yellow-green bracts that look like flowers. Exudes milky latex sap when broken — wear gloves, the sap irritates skin and is toxic to livestock. Spreads by deep roots and explosive seed capsules. See our Leafy Spurge plant page for the full profile.

Common Tansy (Tanacetum vulgare)

A tall plant (often 1–1.5 m) with fern-like aromatic leaves and flat-topped clusters of button-like yellow flowers. Often planted historically as an ornamental, which is how it escaped into ditches and fields. Toxic to cattle and horses in quantity. See our Common Tansy plant page for more.

Common Mullein (Verbascum thapsus)

A dramatic biennial — first year produces a rosette of huge fuzzy silver-grey leaves, second year sends up a yellow-flowered spike up to 2 m tall. One plant produces over 100,000 long-lived seeds. See our Common Mullein plant page for the full profile.

Oxeye Daisy (Leucanthemum vulgare)

Looks like the classic Shasta daisy — white petals, yellow centre, on stems 30–60 cm tall. Pretty, which is the problem: widely planted in wildflower mixes before it was recognized as invasive. A single plant produces 25,000+ seeds that stay viable in soil for decades. See our Oxeye Daisy plant page for more.

Scentless Chamomile (Tripleurospermum inodorum)

Another daisy lookalike — white petals, yellow centre — but with finely dissected ferny leaves and (as the name says) no scent when crushed. Often mistaken for harmless pineapple weed or true chamomile. Produces up to 1 million seeds per plant. See our Scentless Chamomile plant page for more.

Yellow & Dalmatian Toadflax (Linaria vulgaris, L. dalmatica)

Snapdragon-like yellow flowers on plants 30–100 cm tall. Looks cheerful and is sometimes sold as “butter and eggs.” Spreads aggressively by root and seed; almost impossible to eradicate once established. See our Yellow Toadflax and Dalmatian Toadflax plant pages.

Creeping Bellflower (Campanula rapunculoides)

An Edmonton and Calgary garden nightmare. Looks like a pretty purple bellflower, often 60–100 cm tall. Spreads by deep brittle taproots that can survive 8–10 cm underground — tilling makes it worse. Not to be confused with Alberta’s native Harebell (Campanula rotundifolia), which is smaller, more delicate, and non-invasive. See our Creeping Bellflower plant page for removal tips.

First steps: what to do when you spot one

1. Confirm the ID. Noxious weeds often have harmless lookalikes (Creeping Bellflower vs Harebell, Scentless Chamomile vs Pineapple Weed). Use our plant catalogue, cross-check with albertaplantid.ca, and if uncertain send a photo to your municipal Agricultural Fieldman.
2. Assess the infestation size. A couple of plants in a flowerbed is a 10-minute job. A 10 m² patch along the back fence is a season-long project. Match your method to the scale.
3. Act before flowering where possible. Removing a noxious weed after it has set seed means you’re fighting the parent plant and the seedbank it just dropped. Spring and early summer are golden windows.
4. Document & report. Take a photo before you remove it. Report sightings of prohibited noxious species to your municipality — they may send someone out to help, especially for species like giant hogweed that can burn skin.

Removal methods

Mechanical (digging, pulling, mowing)

The cleanest option for small infestations. Dig out the entire root system. For species that spread by rhizomes (Canada thistle, leafy spurge, creeping bellflower), any root fragment left behind will regrow, so be thorough. Moisten the soil the day before to make the whole root come up.

Repeated mowing before flowering can eventually exhaust biennial and some perennial species, but it rarely kills rhizomatous weeds on its own.

Smothering

Cut the weeds down, cover the area with thick cardboard, and pile 15–20 cm of mulch on top. Leave in place for an entire growing season. Works best on broad leafy patches in flowerbed or pathway areas. Check the edges of the smothered zone monthly — rhizomatous weeds will try to escape sideways.

Chemical (herbicide)

For deep-rooted perennials like leafy spurge or Canada thistle, herbicide is often the only realistic option on infestations larger than a flowerbed. Use a selective broadleaf herbicide (2,4-D, clopyralid, or aminopyralid for rural settings) or glyphosate for small spot treatments. Always:

• Read the label in full — some products have restrictions near water or trees.
• Apply on a calm day (wind < 10 km/h) to avoid drift onto your neighbour’s garden.
• Treat in the fall when perennials are pulling resources down to their roots — the herbicide goes with it. Spring applications are less effective on perennial weeds.
• Spot-spray, don’t blanket-spray. You’re aiming at the weed, not the soil or nearby plants.

If you’re uncomfortable using chemicals or have pets and children, contact your municipality — many offer subsidized weed control programs, and some will send a licensed applicator for prohibited noxious species.

Biological control

Alberta has released approved biological control agents (specific insects and fungi) for several major invasives — leafy spurge flea beetles, Canada thistle stem-mining weevils, purple loosestrife beetles. These are long-term, landscape-scale solutions rather than backyard fixes, but if you have a large rural infestation, ask your municipal Agricultural Fieldman whether a release program is active in your area.

Disposal: the part people get wrong

Correct disposal options:

• Bag & landfill. Seal pulled plants (especially any seed heads) in heavy-duty garbage bags and send to landfill through regular waste collection. Most Alberta municipalities accept bagged noxious weeds.
• Let it dry and burn. Only where fire bylaws permit. Spread plants on tarp in the sun for 1–2 weeks first so they dry fully — green material smoulders and can spread seed on the smoke.
• Commercial compost facilities. Industrial windrow composting reaches the 55–65°C sustained temperatures needed to kill weed seeds. A few municipalities (including Edmonton) accept yard waste including noxious weeds in curbside organics bags — confirm with your waste services before dropping off.

Whatever method you use, never toss weeds over the fence into a ditch, field, or natural area. That’s how most infestations in public spaces started.

After removal: replant with natives

Bare soil invites reinvasion. Once you’ve cleared an area, replant quickly with dense native or well-behaved garden plants that will shade out returning weed seedlings. Good Alberta-native choices for recovering infested spots:

• Wild Bergamot and Giant Hyssop — dense, aromatic, pollinator-rich.
• Blanket Flower and Purple Prairie Clover — tough, drought-tolerant for sunny dry spots.
• Common Yarrow and Smooth Aster — quick-establishing groundcovers.
• Blue Grama Grass and Rough Fescue — native grasses that form dense competitive stands.

Monitor the recovered area for at least two seasons — noxious weed seeds in the soil will keep sprouting as the canopy opens up, and the first year is the most vulnerable.

Who to call if you need help

• Rural landowners: your county or municipal district has an Agricultural Fieldman— a specialist whose job is helping producers and rural residents with weed control. They’re a free, expert resource.
• Urban residents:call 311 (or your city’s parks department) for identification help and to report infestations in parks, boulevards, and public land.
• Suspected prohibited noxious weeds (giant hogweed, saltcedar, yellow starthistle, etc.): do not handle yourself. Giant hogweed sap causes severe skin burns. Report immediately and let trained crews remove it.
• Provincial resources:Alberta Agriculture and Irrigation maintains identification guides and the current weed list — search “Alberta Weed Control Act” for the full regulation.

A final note

Removing a noxious weed feels small, but it isn’t. Every plant you take out before it flowers prevents thousands of seeds from blowing across your neighbourhood. Every native you plant in its place is habitat for pollinators and wildlife that have fewer and fewer places to go. A couple of afternoons a year, done with good identification and good disposal, makes a real difference.

Browse all plants currently flagged introduced or invasive in our catalogue by filtering the plant directory to “Invasive / Noxious”.