Purple Loosestrife
Lythrum salicaria
A wetland invader with striking spikes of magenta-purple flowers in summer. It forms dense stands along ponds, ditches, and shorelines, crowding out native wetland plants.
Purple loosestrife — tall spikes of magenta-purple flowers on square stems.
Image source: Purple loosestrife identification fact sheet (educational reference)
At a glance
- Key clue
- Bright magenta-purple flower spikes in wet areas
- Best months
- July to September, when the bright purple flower spikes are in bloom
- Often found
- Wetland / pond edge, Ravine edge, Vacant lot
- Easiest to remove
- Early summer (dig before seeding)
Why it's prohibited
Purple loosestrife takes over wet areas, replacing the native plants that wetland birds, fish, and insects depend on. A single plant can produce huge numbers of seeds, letting it spread rapidly along shorelines and ditches.
Main identification features
- Tall spikes of bright magenta-purple flowers in mid-to-late summer
- Square or angled stems, often 1–2 m tall
- Narrow, lance-shaped leaves in opposite pairs or whorls
- Forms dense, showy purple stands in wet ground
- Woody base on older plants with many stems
Similar plants & look-alikes
- Fireweed — Fireweed has rounder pinker flowers, round stems, and grows in dry, open or burned ground, not wetlands.
- Blazing star (Liatris) — Blazing star is a garden plant with fluffier flower spikes and grass-like leaves, typically in dry beds.
Month-by-month identification timeline
July to September, when the bright purple flower spikes are in bloom.
April–May (Early spring)
· 10–40 cmNew shoots emerge from the woody root crown; lance-shaped leaves appear in pairs.
Paired lance-shaped leaves on square stems.
May–June (Late spring)
· 0.5–1.2 mStems grow tall and bushy in wet ground.
Upright square stems thickening into clumps.
July–August (Summer)
· 1–2 mTall spikes of vivid magenta-purple flowers open — very showy.
Bright magenta-purple flower spikes — easiest ID.
August–September (Late summer)
Flowers fade to small seed capsules that release vast numbers of tiny seeds.
Spikes turn to seed capsules (huge seed output).
Fall–winter (Dormant)
Stems dry to reddish-brown stalks; the woody crown survives winter.
Dry reddish-brown stalks; persistent root crown.
Growth-stage photo gallery
Photos of purple loosestrife at different growth stages — note the visual features described under each one to identify it confidently.
Tall spikes of bright magenta-purple flowers on square stems.
A showy clump of purple flower spikes rising above wetland foliage.
A wetland or field taken over by a sea of magenta loosestrife.
Click any photo to enlarge. Image source: Purple loosestrife identification fact sheet (educational reference).
How to remove it safely
Safest resident-friendly approach
For a few plants, dig out the whole root crown with a spade before they set seed — pulling alone often leaves roots behind. Cut off and bag the flower spikes first so the seeds can't scatter. In wet shoreline areas, take extra care and check whether permits apply near water.
Tools & protection
- Gloves
- Spade or garden fork
- Bags for flower spikes and roots
Best time of year
Early summer at flowering, before seeds form; remove root crowns when soil is workable.
Monitoring
Check the area for several years, as the seed bank in the soil can keep producing new plants.
Prevent regrowth
Remove the entire root crown and monitor for seedlings; replant wet areas with native plants.
What not to do
- Don't let it go to seed — one plant can release enormous numbers of seeds
- Don't leave cut spikes lying around; bag them
Disposal
Bag flower spikes and roots for the garbage so seeds aren't spread. Do not compost flowering or seeding material.
Safety cautions
- Low direct risk to people — basic gloves are enough
- Take care on soft, wet ground near ponds and shorelines
- Bag flower spikes to stop seeds from spreading
When to get professional help
Recommended for large stands or shoreline/wetland areas where permits and careful methods may be required near water.
Bag and garbage flower spikes and roots; never compost seeding material. Avoid spreading seeds near water.
Sources
Report a prohibited plant
Found this plant growing on a property? Report it to the City through official Toronto 311.
Report through Toronto 311This page is provided for general educational and reference purposes only. Plant identification results are not a legal determination. Always confirm prohibited plant information using official City of Toronto resources. For hazardous species or large infestations, consider seeking professional advice.
Image credits & usage
Plant photographs are reproduced for non-commercial public education and identification reference only. Sources include Ontario weed-identification (OMAFRA / Ontario CropIPM) and invasive-species fact-sheet materials; all image rights remain with their respective owners. If you are a rights holder with a concern, please contact us through the Feedback page. Photos on this page: Purple loosestrife identification fact sheet (educational reference). Contact us.