Some plants are…just evil. Learn how not to plant them.

dog-strangling vine, aka swallow wort

Some plants are the poster children of invasive species awareness campaigns. We’ve all heard about Purple Loosestrife (Lythrum salicaria), and FWG works hard to raise awareness about Dog-strangling Vine (Cynanchum rossicum /Vincetoxicum rossicum) and Buckthorn (both glossy Rhamnus frangula and common Rhamnus cathartica). However, some attractive lesser-known plants with invasive tendencies are still sold as ornamentals in nurseries or gifte­d between friends. They are no less invasive, but information campaigns in the garden industry aren’t always effective so these lovely plantes fatales are still grown and sold to consumers who plant them at home, perpetuating sources of invasive spread. There isn’t any malice involved, just a lack of information or even warnings on labels.

As a consumer planning your garden, you are on the front lines of the solution since you have the right to tell a nursery their stock is invasive. Some plants that have invasive tendencies are perfectly legal to sell, and a nursery doesn’t have to stop making them available. In these cases, you can help by educating your friends and family. Moreover, encourage your friends to evaluate their own gardens for potential invasive plants. Nothing is more painful than pulling out a beautiful plant, but we do have a responsibility as gardeners to protect the greater ecosystems around us.

There are several rules to follow to ensure you are a responsible plant consumer. While it may increase the effort involved in garden planning, the outcome is an eco-responsible garden.

  1. Always check scientific names. Latin names are the first line of defence for the eco-responsible garden. Many plants look similar or are of the same genus, but the invasiveness depends on species. If a nursery doesn’t have the Latin name available, walk away. The Internet is the best source for checking whether a particular species is possibly invasive in your area.
  2. Consider pathways of escape from your garden. A plant may not be equally nefarious in all situations. Most creeping ground covers should NEVER be planted in rural or semi-rural areas, but in the urban garden are beautiful additions. Likewise, some trees are horribly invasive anywhere outside an urban tree sidewalk wasteland. If you are adjacent to a park, NCC land or other open space, be triply vigilant and careful with your plant selections.
  3. Consider gifts with suspicion. Your friend may not know what their plant really is or have the wrong name. Ask where they obtained the plant, its habits in their garden and, when in doubt, don’t plant it out. Err on the side of caution.
  4. Not all heirlooms are created equal. Don’t be fooled when you read that no country garden is complete without plant X. Many invasive species in Canada were introduced by well-meaning gardeners once upon a time.
  5. If it seems too good to be true, it probably is invasive. That impossible shade spot suddenly covered with green? The dry, dusty dead zone where nothing would grow? If something is flourishing, investigate why and be vigilant.

Invasive plant councils are found in many provinces and have useful information, while conservation authorities in Ontario can be great resources about what is invasive. Don’t ever compost something that could be invasive – bag it carefully and relegate it to the dump. Don’t throw it into a ditch or over the fence!

See – http://www.ofnc.ca/fletcher/research/swallowwort/index_e.php#disposal

Some people may argue that they monitor their climbers and creepers, so why should they not keep them in their gardens? The issue is that not all gardeners will be as conscientious, and you don’t know who will own your garden once you move on. Walking in Ontario, it is possible to see where old homes once were in the country due to lilacs and periwinkles all over the place! Moreover, for any berry-producing plant or obvious seed head, birds will readily snack and spread through their faeces any plant you may consider secure. Be especially wary of any seed mixes labelled for wild areas – they are not always appropriate for the Ottawa Valley, and can contain plants invasive here.

Visit the Ontario Invasive Plants Council, the Canadian Food Inspection Agency or Landscape Ontario for more information about ornamental escapees.

Below are lists of some terrestrial plants that can be invasive in the Ottawa Valley divided into categories: Wary, Avoid and Destroy. This is not an exhaustive list, but a good place to start.

Wary

Baby’s Breath Gypsophila paniculata flower Escapes as its seed is spread.
Caragana / Siberian Pea Shrub Caragana arborescens shrub Able to establish quickly in poor soils, spreads by seed and sprouting rootstock.
Creeping Bellflower Campanula rapunculoides flower Escapes as its seed is spread. Deep, fleshy roots spread through the garden and cannot be removed.
Dame’s Rocket Hesperis matronalis flower Member of the mustard family is a prolific seed producer and often ends up in “wildflower” mixes.
English Ivy Hedera helix groundcover / climber Use only in urban areas. Can overcome trees and aggressively cover other plants.
Goutweed (aka Bishop’s Weed) Aegopodium podgraria groundcover Use only in urban areas. Escapes easily into naturalised landscapes. Can grow from seed and tiny leftover roots. Green and white variety as well as medium green.
Jerusalem Artichoke Helianthus tuberosa tuber Delicious in the kitchen, Jerusalem Artichokes can easily escape and spread from bits of root left in the ground. Grow in containers or beds away from lot lines.
Maltese Cross Lychnis chalcedonica flower Escapes as its seed is spread.
Periwinkle Vinca minor groundcover Use only in urban areas. Escapes easily into naturalised landscapes.
some Bamboo species Varies grass Bamboo that spreads through rhizomes (roots) can escape and take over. Do your research to find a less aggressive bamboo, and contain it so it cannot spread beyond where you wish it to go.
Wild Caraway Carum carvi herb Same plant as caraway seed in the grocery store. Seed can escape and displace native grassland plants.
Winged Euonymous (Burning Bush) Euonymus alatus shrub Beautiful ornamental that escapes captivity easily, creating clumps in naturalised areas especially woodlands. There is a native species type, Euonymus atropurpureus.

Avoid

Amur Maple Acer ginnala tree Profuse seed producer can escape when seed is moved by wind or wildlife. Forms dense thickets.
European Barberry Berberis vulgaris shrub Spreads by seed located in berries. Plant is the alternate host for wheat rust fungus (Puccinia graminis), a grass-infecting rust fungus that is a serious fungal disease of wheat and related grains.
Himalayan Balsam Impatiens glandulifera shrub Fast-growing, can overcome other plants. Spreads most easily by seed. Major invasive problem inEuropewith no known biological control.
Norway Maple Acer platanoides tree Aggressive growth habit, will shade out understorey plants, out-compete native maples and rapidly spread through seed. The only reason to ever grow a Norway Maple is if you live downtown and no other tree will grow. Even then, why bother? You’ll have nothing survive the shade beneath!
Salt-Cedar Tamarix spp tree Originally introduced salt-tolerant species for soil stabilisation in moist areas, can aggressively outcompete and make soil even saltier inhibiting other species. Spreads quickly by seed or root bits.
St. John’s-Wort Hypericum perforatum shrub Creeping-rooted perennial which forms colonies. Also spreads through seed. It is listed as a noxious weed in more than 20 countries and poisons animal grazers.
Tartarian Honeysuckle Lonicera tatarica shrub Touted as a good shrub for attracting birds because of its fruit, but it escapes and creates mono-thickets.
Yellow Clematis Clematis tangutica climber Aggressive grower, the seed is windborne and spreads easily. There is a native alternative.
Yellow Flag Iris Iris pseudacorus flower Spreads by seed and rhizomes, creating dense clumps in moist areas replace native species. Poisonous to grazers and can cause contact dermatitis in people. No biological control exists.

Destroy

Common Reed Grass Phragmites australis grass Forms dense clumps in wet areas, outcompeting native species. Spreads through seed and rhizomes.
Giant Hogweed Heracleum mantegazzianum large herb Reproduces quickly by seed. Causes contact dermatitis, ungrazeable.
Japanese Knotweed Polygonum cuspidatum clumper Looks similar to bamboo but is not, and is hugely invasive in various national parks. Can regrow from even a portion of the root, spread by seed and creep far beneath concrete to pop up among tree roots making annihilation difficult. If you see this in a nursery, insist on its destruction (not composting).
Oriental Bittersweet Vine Celastrus orbiculatus climber Easily confused with, and can hybridise with, native bittersweet vine (Celastrus scandens). Can be mislabelled in nurseries. Very aggressive growing habit.
Purple Loosestrife Lythrum salicaria clumper Can hybridise with ornamental cultivars, and seed mixes are not guaranteed to be free of the known invasive variety. Do not confuse with Yellow loosestrife (Lysimachia terrestris) which is native but can also be a quick coloniser.
Reed Canary Grass Phalaris arundinacea grass Forms dense clumps in wet areas, outcompeting native species. Spreads through seed and rhizomes.
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2 thoughts on “Some plants are…just evil. Learn how not to plant them.

  1. Might we want to add Russian Olive (tree/shrub) to the list? It is commonly sold at local nurseries. I just bought one but will be returning it after googling has alerted me to its problematic nature.

    • Elaeagnus angustifolia is a non-native small tree popular for its ability to thrive in poor soils, urban environments and its showy foliage. We haven’t had direct experience with Russian Olive escaping or causing problems at FWG, but we would certainly not recommend that anyone plant it – especially in rural or semi-rural environs.

      If you like the texture of the leaves, consider one of our many beautiful, native willows.

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