Invasive Ornamental Plants & Native Alternatives

Weedy Horticulturals and Native Alternatives

Chet Neufeld, Executive Director, Native Plant Society of Saskatchewan

I don’t know any gardener whose favourite season is winter.  All a person can do is plan, wait and perhaps start a few plants from seed in a sunny room.  With all this time on your hands, it’s a really good time to think about what you like and don’t like about your yard.

You might want to plant something new in a corner of your yard or you might want to replace some old, tired looking plants with new ones.  And while you’re thinking about what you want to plant and where, consider what your plant choices will do in the future.

While the mature size and shape of plants are important to the overall look and function of your yard, I would argue that the potential spread of plants is just as important.  Will the plant stay more or less where it was put?  If the answer is “no” or “I’m not sure”, perhaps you should consider another alternative.

I have talked to many gardeners that have asked me how to get rid of plants that began taking over their flower beds and even creeping into their lawn.  While my answers differ depending on the species in question, it would have been easiest if they had not planted it in the first place (although hindsight is 20/20).  Worse yet, some invasive plants don’t stop at fence lines and continue to spread into their neighbour’s yard, down the road or into surrounding natural areas.

For example, the City of Saskatoon and Meewasin Valley Authority spend tens of thousands of dollars trying to eradicate European buckthorn (Rhamnus cathartica) from the South Saskatchewan River valley; the infestation was a result of horticultural introductions throughout the city.  There are hundreds of examples of garden plants escaping into the wild and wreaking havoc, most notably purple loosestrife (Lythrum salicaria) which showed up in the lake near my house for the first time in the summer of 2008.

We as gardeners have a responsibility to ensure our gardens are environmentally-friendly.  Does this mean that we have to sacrifice the beauty of our gardens?  Absolutely not!  For every invasive plant, there is another plant with roughly the same look and function that will stay where it was put.  With that, I’ve compiled a short list of new alternatives to old problem plants.

FLOWERS
Invasive Horticultural Plant Problem Native Alternative Benefits
Shasta daisy (Leucanthemum superbum), Ox-eye daisy (Leucanthemum vulgare) Its seeds readily establish in areas outside of where it was planted, such as natural areas. Many flowered aster (Aster ericoides) Very drought hardy and blooms for a long time.
Creeping bellflower (Campanula rapunculoides) As its name indicates, it creeps – everywhere! Harebell (Campanula rotundifolia), Low larkspur (Delphinium bicolor) These beautiful flowers will attract butterflies.
Common tansy (Tanacetum vulgare) Adult plants can produce up to 50,000 seeds that spread everywhere. Native sunflowers (Helianthus sp.) Sunflowers are drought-tolerant, mid-to late summer bloomers and will stay where they’re planted.
German chamomile (Matricaria recutita), Scentless chamomile (Tripleurospermum inodorum) Produces a large amount of seed that spreads to other parts of your yard and natural areas. Many flowered aster (Aster ericoides) Very drought hardy and blooms for a long time.
Himalayan balsam / Poor man’s orchid (Impatiens glandulifera) Spreads to natural areas, particularly along rivers and creeks. Joe pye (Eupatorium maculatum), Spotted touch-me-not (Impatiens biflora) These showy flowers will attract butterflies.
Snow-on-the-mountain / Goutweed (Aegopodium podagraria) This creeper invades natural areas.  Also, the plant is poisonous to children and pets, and the oils can cause rashes. Sarsaparilla (Aralia nudicaulis) This shade-lover has large leaves and interesting little flowers.
WATER GARDEN PLANTS
Invasive Horticultural Plant Problem Native Alternative Benefits
Yellow floating heart (Nymphoides peltata) Can escape into ponds and lakes, where it covers the water surface and shades out aquatic life.  It also makes water-based recreational activities very difficult. Yellow pondlily (Nuphar variegata) Arguably one of the most beautiful, showy flowers.  Blooms last for months.
Water chestnut (Trapa natans) Problems are much the same as yellow floating heart.  Water chestnut produces spiky seed pods that can puncture feet if stepped on – even wearing leather soles! Yellow pondlily (Nuphar variegata) Arguably one of the most beautiful, showy flowers.  Blooms last for months.
Parrot feather (Myriophyllum aquaticum) Spreads to lakes where it chokes out native aquatic vegetation and makes the area useless for fish. Hornwort (Ceratophyllum demersum) Oxygenates the water and provides habitat for fish.
Flowering rush (Butomus umbellatus) Crowds out beneficial aquatic plants and destroys waterfowl nesting habitat and fish rearing areas. Joe-pye (Eupatorium maculatum) Great for pollinators and very attractive on its own or amongst other flowers.
Shrubs
Invasive Horticultural Plant Problem Native Alternative Benefits
Sea buckthorn (Hippophae rhamnoides) Produces a large amount of orange fruit, each containing a seed.  These are dispersed by wildlife which then grow wherever they are deposited. Thorny buffaloberry (Shepherdia argentea), Hawthorn (Crataegus columbiana) Thorny buffaloberry produces bright red fruit that birds love.  Hawthorn has interesting, curved barbs.  Both will make excellent bird nesting shrubs and form an impenetrable barrier.
Common / European buckthorn (Rhamnus cathartica), Alder / Glossy buckthorn (Rhamnus frangula) Easily spreads to natural areas where it will shade out and displace other desirable plants, reducing biodiversity. Thorny buffaloberry (Shepherdia argentea), Hawthorn (Crataegus columbiana) Thorny buffaloberry produces bright red fruit that birds love.  Hawthorn has interesting, curved barbs.  Both will make excellent bird nesting shrubs and form an inpenetrable barrier.
Salt cedar (Tamarix spp.) Produces huge amounts of seed that can establish in the wild, where they will consume hundreds of litres of water a day, drying up local aquifers and concentrating salts at the soil surface which renders it almost useless for growing anything. Juniper (Juniperus communis), Cedar spp. (Thuja spp.) Junipers are extremely tolerant of drought, cold and foot traffic.  Cedars need the right conditions but are a welcome addition where they can be grown.
TREES
Invasive Horticultural Plant Problem Native Alternative Benefits
Russian olive (Elaeagnus angustifolia) Russian olive is a particularly bad problem along waterways, where it displaces native poplars (Populus spp.) and changes the structure and function of shorelines. Willow spp. (Salix spp.) Willows are maintenance free and grow quickly.
Siberian / Manchurian elm (Ulmus pumila) The seeds of this tree are carried by the wind and establish almost anywhere.  Those who have it are constantly pulling seedlings out of their flower beds.  They are unwanted invaders in natural areas as well. American elm (Ulmus americana), Green ash (Fraxinus pennsylvanica) While the American elm also produces seed, it is less aggressive than the Siberian elm.  It is also the iconic shade tree of old neighbourhoods and is loved by birds and joggers alike for the shade it provides.  Green ash is a good alternative if concerned about Dutch elm disease.

When buying plants or seeds for your yard, do your homework and make sure that you’re not buying pretty weeds.  Look at the tag; if it has descriptions such as “vigorous spreader”, “readily self-seeds” or “easily naturalizes”, BEWARE!  Ask your local greenhouse expert about the plant you intend to buy and if it will spread.  They can also suggest similar plants or seeds to purchase that aren’t aggressive.  Another good resource regarding the potential invasiveness of horticultural plants is the internet.  I Googled “common tansy” and every result on the first page warned that it was a plant to be avoided.

Be wary of buying seeds over the internet or by mail order.  What might be a pretty flower at a mail order company in the U.S. might be a noxious weed here.  Also, unless you’re dealing with  a reputable seller, the seed you buy could contain weed seeds or in some cases be a completely different species than what you ordered.  Never buy “wildflower” mixes unless you are completely sure that all of the species in the mix are safe to plant.  Baby’s breath (Gypsophila paniculata) is a common component of wildflower mixes and is a noxious weed.  If you want a wildflower mix, make your own!  That way you can personalize the mix to the colors, sizes and shapes that you want.

If you’re removing unwanted invasive plants, be sure to dispose of them properly.  Bag and burn them or put the bag in the trash where it will go to the landfill.  Bagging the plants ensures that no seed will escape on its way to being disposed of.  Don’t compost the plants as there won’t be enough heat generated to kill any seeds or rhizomes that may be present.  If you have any questions or concerns about what you might be growing or what you would like to grow, or would like sources for the plants I’ve listed in this article, contact me at info@npss.sk.ca.

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