Joyce Hostyn

Kingston’s prohibited plants

On August 14, 2024, Kingston’s new yard bylaw came into effect, removing height restrictions and vague, culturally biased, aesthetically-based terms such as “overgrown”, “unsightly”, “weeds”, “messy”, and “heavy undergrowth” that prevented people from naturalizing their yards in support of biodiversity and climate resilience. An appendix to the bylaw contains a short list of plants that are prohibited due to their risk to our urban ecosystem or to human health. Turfgrass is defined and continues to be regulated with a height restriction of 20 cm.

With these changes, Kingston has become a Canadian leader in supporting naturalized yards. If you’re not in Kingston, you can join a Canada-wide campaign to get your local government to update their bylaws.

A group of conservationists in Canada — including the Canadian Society of Landscape Architects, Canadian Wildlife Federation, David Suzuki Foundation, Ecological Design Lab at Toronto Metropolitan University and author and environmental advocate Lorraine Johnson — recently published an open letter urging municipal bylaw reforms to support habitat garden development.

David Suzuki, It’s time to ditch the lawn and go natural

Prohibited plants

Get to know these prohibited plants. Monitor your yard regularly to prevent them from establishing themselves and spreading in your neighbourhood or into natural areas. Eradication is easy with early identification and action. If you wait until they are well established, eradication is difficult.

Buckthorn (Rhamnus cathartica), (Rhamnus cathartica)

Common and Glossy Buckthorn are large invasive shrubs or small trees that are taking over Kingston’s urban forest. Their seeds are spread by birds. Pull when small. Dig out larger plants with a spade, mattock, or weed wrench tool, ensuring you get the root system to avoid re-sprouting. Dispose of ripe berries in garbage.

Confused with our native Alderleaf Buckthorn (Rhamnus alnifolia), which is much smaller and has no thorns.

Dog-Strangling Vine

Dog-Strangling Vine is an invasive twining vine popping up all over Kingston that quickly spreads to form colonies, smothering other vegetation. It’s extremely difficult to eradicate once established. Monarchs sometimes confuse them with our native Milkweeds and lay eggs on them. The caterpillars starve as the leaves don’t have the nutrients they need. Dig out plants if possible. If you can’t dig out the plant, cut below soil level to starve the plant (pulling often splinters the roots and produces more plants). Or tarp the area. Solarize to prevent re-sprouting. Dispose of seedpods in garbage.

Confused with Milkweed Species (Asclepias spp.), Dogbane (Apocynum spp.)

Japanese Knotweed (Reynoutria japonica var. japonica)

Japanese Knotweed is an invasive perennial that quickly forms dense thickets of bamboo-like vegetation with roots that are strong enough to grow through concrete, asphalt, and building foundations. Dig out young plants (including rhizomes). Larger plants are extremely difficult to eradicate. Tarp the area. Or cut the stalks at least once a month throughout the growing season to weaken the rhizomes (may take 5 years).

Confused with Giant Fleece Flower (Persicaria polymorpha).

Canada Thistle (Cirsium arvense)

Canada Thistle is a perennial with a creeping root system and sharp spines. Solarize or hand pull. Repeated hand pulling is necessary to eradicate as Canada Thistle has an extensive root system that can grow as much as 6m in a single season. Solarize roots as each section of root can form a new plant. Wear thick, protective gloves.

Confused with Bull Thistle (Cirsium vulgare), Spotted Knapweed, (Centaurea stoebe spp. micranthos), Nodding Thistle (Carduus nutans L.), and our native Field Thistle (Cirsium discolor).

Garlic Mustard (Alliaria petiolata)

Garlic Mustard is an invasive biennial that quickly takes over shaded areas. The taproot exudes chemicals that modify the soil, creating conditions hostile to native plants. Leaves have a strong garlic odour when crushed. Hand pull basal rosettes and second year plants before they flower. Cut flowering plants to the ground to prevent seed production. Solarize to prevent re-sprouting. Dispose of flowers and seedheads in garbage.

Giant Hogweed (Heracleum mantegazzianum)

Image: jfgodeau/iNaturalist

Giant Hogweed is an invasive monocarpic perennial not yet seen in the Kingston area, though may already be here as they take 3-5 years to flower which is when people usually recognize them. After producing 1,500 to 100,000 seeds, the plant dies. Giant Hogweed contains a phototoxic sap which reacts with ultra-violet (UV) light to cause a burn-like rash (phytophotodermatitis) in some people. Wearing protective clothing, dig out individual plants or cut the stem below ground level with a shovel, spade or machete before seed heads mature. Dispose of seedheads in garbage.

Confused with Queen’s Anne Lace (Daucus carota), Wild Parsnip (Pastinaca sativa), Cow Parsnip (Heracleum maximum), Angelica (Angelica atropurpurea), and Elderberry (Sambucus spp.).

Phragmites (Phragmites australis subs. australis)

Phragmites is a tall invasive perennial grass that grows in ditches, wetspots, and disturbed wetlands. Dig out or cut to drown. Solarize rhizomes as they can regrow. Dispose of seedheads in the garbage.

Confused with Phragmites australis subsp. americanus.

Poison Ivy (Toxicodendron radicans)

Poison Ivy is a native perennial vine. Poison Ivy contains urushiol, a chemical which causes a burning, itching rash in 80% of people. Pull out the plants in spring when the ground is still wet, getting as much of the root system as possible. Repeat as needed. Wear protective clothing and wash everything that could have come into contact with the plant, including shoes, laces, and tools. Dispose of plants in the garbage as even the dead plants can cause rashes.

Confused with American Hog-Peanut (Amphicarpaea bracteata), poison oak (Toxicodendron pubescens), and Poison Sumac (Toxicodendron vernix).

Purple Loosestrife (Lythrum salicaria)

Purple Loosestrife is an invasive perennial that appears in ditches and wet spots and is a threat to the wetlands in the Kingston area. Dig out when in flower (June, July and early August), removing as much of the root system as possible to reduce re-growth. Solarize before composting to prevent re-sprouting. Dispose of seedheads in the garbage.

Confused with Fireweed (Chamerion angustifolium), Blue Vervain
(Verbena hastata), Blazing Stars (Liatris spp.), Winged Loosestrife (Lythrum alatum), and Swamp Loosestrife (Decodon verticillatus).

Wild Parsnip (Pastinaca sativa)

Wild Parsnip is an invasive biennial. Wild Parsnip and Garden Parsnip are the same species and both have the potential to cause a burn-like rash (phytophotodermatitis) in some people. Wearing protective clothing, pull or cut Wild Parsnip before they go to seed (late June and early July). Dispose of seedheads in the garbage.

Confused with Golden Alexander (Zizia aurea).

Ragweed (Ambrosia artemisiifolia)

Ragweed is a native annual that you’ll mostly likely find growing in disturbed areas along your sidewalk or the road in areas with fewer trees, but also pops up in lawns and gardens. Ragweed is easy to pull out by hand. Spreads by seed so pull before seeding.

Confused with Queen’s Anne Lace (Daucus carota), Biennial Wormwood (Artemisia biennis), Goldenrod (Solidago).

Report invasive species

Some of the plants on the prohibited species list are listed as invasive species in Ontario. If you see invasive species on public land, you can report them:

“You are on the front lines of monitoring changes in the landscape and will be essential for early detection, reporting and control of invasive plants. It won’t be an easy task – many of these species very quickly spread to new areas, grow rapidly and may require continued management for many years. However, through actions of private landowners we can limit the impact of invasive plants on the ecology and economy of Ontario, and improve the health of our lands and waters for our children and grandchildren.”

Dan Kraus, Manager of Conservation Science and Planning Nature Conservancy of Canada – Ontario Region, Landowner’s guide to managing and controlling invasive plants in Ontario