Considerations for SW Ontario Gardeners

photo of sky-blue aster / Symphyotrichum oolentangiense — Sky-Blue Aster (Symphyotrichum oolentangiense), one of several asters native to Southwestern Ontario. Photo credit: Joshua Mayer, Flickr

The surge of interest in native plants is a welcome development for gardeners interested in supporting pollinators and wildlife. Whether we’re trying to attract birds and butterflies, to provide habitat for at-risk native pollinators and other wildlife, or to increase biodiversity for garden health and resilience, native plants are in demand. For many gardeners the world of native plants represents a fork in the road of their gardening journey. Becoming a native plant gardener is far more than just buying different species—it’s a new way of thinking about what makes a garden healthy, beautiful, and even useful. But as we learn about the “why” of ecological gardening, we are faced also with the “what.” What IS a native plant? How can we tell if a plant is native or not?

Pervasive ≠ Native

The wild-looking plants and shrubs we see all over the place—in ditches, fields, and conservation areas—surely they’re native, right? Not necessarily. Many roadside and forest wildflowers (dandelions, dames rocket, Queen Anne’s lace, mullein, blueweed, scilla, chicory, ditch lily, celandine poppy and coltsfoot, to name a few) are ubiquitous. But they’ve not always been here. They’re naturalized but they’re not native. Some, such as garlic mustard and plantain, are escapees from gardens planted by early settlers. Some, like Achillea millefolium (white yarrow) have been here so long and have such inconsistent genetics that no one is really sure if they’re native or not. Other popular plants that are often mistaken for native include: common mint, thyme, clover, periwinkle, hosta, lily of the valley, forsythia, lilac, rose-of-sharon, and miscanthus.

Plants that are native to a different continent are called “exotics”. In North America, goldenrod (Solidago spp.) is native; in England, it’s exotic. Some exotics are benign, well-behaved garden residents—your delphiniums, Jackmanii clematis, and peonies are never going to show up on an invasive species list. Several exotics are invasive, doing damage to forests and natural lands when they escape from gardens, which they regularly do. Some of them, such as Buddleia (butterfly bush) are being closely watched for signs of invasiveness, as climate change provides new growing conditions and southern invasive species move north.

Many meanings of “native”

How can we tell if a plant is native or not? Unfortunately there is no easy, cut-and-dried answer. “Is it native” might be rephrased as “Is it native enough”—for our own gardens and gardening goals. “What is native” can depend on one’s area of specialization or interest. Botanists will see the concept differently than, say, ecologists or restoration professionals, but that’s another long and fascinating discussion for another time. We’re going to look at native plants from a southwestern Ontario gardener’s perspective.

So let’s use the wide-angle lens and look at definitions. Here is a fairly straightforward one: a native plant is one that was here before colonization. And here is a more nuanced and equally correct definition: native plants co-evolved with a community of flora and fauna and have functional relationships with them.

Author and activist Lorraine Johnson’s definition is probably the most inclusive, seeing the big picture in all its complexity: “Native plants are species that evolved in association with all the features of a place and developed specific and important functional relationships and interactions that contribute to the specificity and identity of that place.” Lorraine’s “features of a place” leaves room for the abiotic (non-living) aspects of a place such as rocks and geological features (a 200-foot limestone cliff for example) as well as the bodies of water, aquifers, climate, and other things that make one place distinct from all others.

It’s about place

Place is the key to understanding native plants. When we say “native plant” we must always include the place it’s native to. Penstemon strictus, for example, is native to the southern Rocky Mountains, originally inhabiting subalpine zones, valley sagebrush and conifer forests in only a handful of states. Since colonization it’s been spread by humans, becoming naturalized in a wider area in the US southwest. Similarly, some alpine plant species are found only at a certain altitude on certain mountains in the Himalayas.

This excerpt from http://www.canadiantreetours.org/ shows how murky the “native” concept can be:

Eastern redbud's status as a native plant in Canada is based on a single observation on the south end of Pelee Island in 1892. Although officially regarded as extirpated in Ontario, eastern redbud has been successfully planted in various parts of Southern Ontario as an ornamental tree. Offspring of these trees have escaped cultivation and spread to natural areas so eastern redbud can once again be found growing wild. Eastern redbud is native to a large area of the United States, as far south as Florida, and in Mexico. Its exact range pre-European settlement is not clearly known because it has been cultivated for so long and has naturalized in the wild.

Our beautiful Sundial Lupin (Lupinus perennis) is native to oak savannas, a rare habitat in Ontario. If you really want to kill a Sundial Lupin, plant it in clay in your home garden. But seriously, this lupin is a specialist and some restoration professionals argue that every native lupin seed should go to wild habitat where it can actually thrive. Not all native plants are appropriate for commodification.

Here in the northern reaches of North America’s Eastern Deciduous Forest region (in Ontario we sometimes call this the “Carolinian Zone”) we have the most plant diversity in all of Canada. Occupying less than 0.25% of Canada’s landmass, the Carolinian forest provides habitat for over 40% of Canada’s plant species and probably an equally large proportion of vertebrate and invertebrate fauna. Situated at the convergence of three great North American regions (the Boreal Forest to the north, the Great Plains to the southwest, and the Eastern Deciduous Forest to the south and east), this area’s biodiversity is truly amazing—2,545 vascular plants are native here! But because we’re also the most heavily developed, populated, and farmed area in Canada we also have the most species at risk due to habitat loss. The Carolinian zone’s exceptional abundance, as well as the huge threats of species extinction, are what make native plants so fascinating and so important.

Ecosystems, not hardiness zones

graphic of Ontario ecozones and ecoregions — Ontario ecozones and ecoregions

For gardeners, the concept of “place” is often connected to plant hardiness. “Growing zone” or “plant hardiness zone” describe whether plants are likely to survive our winters, using average (cold) temperatures as the main criteria. Although the Federal Ministry of Natural Resources’ excellent climate zone maps have been improved to include heat, precipitation, humidity, and other important determinants of plant hardiness, in the world of native plants, hardiness is not the most appropriate lens.

We need the concept of ecosystem to really understand whether a species belongs to a place. An ecosystem is a community of plants, animals and abiotic (non-living) features that comprise a distinct place. Ecologists have categorized places with similar ecologies into broad groups (ecozones) which are then subdivided into smaller groups (ecoregions and ecodistricts). Ontario’s Ministry of Natural Resources and Forestry has defined three ecozones: Hudson’s Bay Lowlands, Ontario Shield, and Mixedwood Plains. Within the Mixedwood Plains, which comprises most of Southern and Eastern Ontario, there are two ecoregions: 6E (Lake Simcoe-Rideau) and 7E (Lake Erie-Lake Ontario). Each region is made up of smaller ecodistricts. Grimsby ecodistrict (7E-3) at 74,000 hectares is a narrow strip of land below the escarpment from roughly Campbellville to the Niagara River. Visit https://files.ontario.ca/mnrf-ecosystemspart1-accessible-july2018-en-2020-01-16.pdf for a fascinating look at all of Ontario’s zones and regions.

Moving plants

So, to know what plants are native to your area depends on the level of precision (ecozone, region, or district) you’re okay with. Some gardeners will accept “anywhere in the province.” Some want plants that would have been found in a typical ecosystem within a 50 km radius of their backyard. Others will include “near natives”—plants that are not found in southwestern Ontario but are common in the states directly south of us and might have made the leap across Lake Erie or Lake Ontario given another few thousand years. Relying on wind, birds, insects and sometimes waterways to transport seeds, plants simply don’t move very fast.

Even fast-moving plants cannot outpace climate change. Because, unlike animals and insects, plants cannot walk or fly away from areas becoming too hot, dry, or wet for them, some ecologists want to introduce plants into areas north of their native range. Assisted migration, as it’s called, is a controversial practice. The Biodiversity Institute of Ontario at the University of Guelph (https://biodiversity.uoguelph.ca) is a hub for research in this area. There’s a good teaching resource from the Association for Canadian Educational Resources that looks at ecosystems with reference to climate change: https://www.acer-acre.ca/resources/climate-change-in-context/the-presentrecent-past/impacts-2/ecosystems.

Photo of vinca invading forest floor — Vinca / Periwinkle escapes gardens and invades forests. Photo credit: mwms1916 (Flickr)

“Helping” species travel is a job for professionals. Conservation and restoration ecologists look at plant origins in a very specific way, noting variations in disparate local populations and identifying naturally occurring genotypes. Plants that evolved in a certain geographical region have coadapted gene complexes, making them more likely to survive and reproduce there. Well-meaning gardeners who add plants to conservation areas and other naturalized spaces, whether public or private, can do more harm than they may realize. Just as we should never remove plants from the wild, neither should we introduce them. To learn more about the genetic aspects of plant diversity in Ontario, visit https://fgca.net/, the Forest Gene Conservation Association.

Doing the research

Being aware of issues around plant conservation may help us decide what to plant in the backyard garden, but let’s return to the question of “what is native.” For recent enthusiasts looking for native plants, the catalogue of a local native plant supplier might be the first port of call. Unlike most general growers doing retail, these specialty nurseries are conscientious about sourcing their plants. Some can even point to the local population from which their stock originated. Specialty growers who propagate from seed (and most of them do) will be able to tell you whether the seeds were ethically harvested from wild populations, harvested from “captive” or purpose-grown populations, or purchased from a bulk/wholesale supplier.

But contacting growers can be a lot of work for someone who simply wants more native plants in her garden. An easier way to learn what species are native to your area is to consult one of the many authoritative lists available online. Here’s how to go about learning whether a certain plant, perhaps one from your own garden, is native or not.

What’s its name?

Before tackling the lists we need to accept, perhaps grudgingly, some botanical Latin —binomial nomenclature—into our vocabulary. Pronunciation doesn’t matter so much, but the species name does. Among the many online resources for learning the basics, this short-and-sweet one from the Wisconsin Master Gardeners is easy to understand: https://mastergardener.extension.wisc.edu/files/2015/12/plantnames.pdf .

If you only have a photo, try using the iNaturalist app to help provide an identification. Recommended by professional botanists and naturalists, iNaturalist has stringent verification protocols and a huge user group, making it an excellent tool for citizen science. Reliable identification is also possible with a dichotomous key. GoBotany (https://gobotany.nativeplanttrust.org), the web site of the New England Native Plant Trust, has a very good key. So does the USDA’s Natural Resources Conservation Service https://plants.sc.egov.usda.gov/java/.

You can also use social media for help with plant ID. Facebook has some reliable groups. Try https://www.facebook.com/groups/156706504394635 “Plant Identification” or https://www.facebook.com/groups/742678512517908 “Plant Identification Southwestern Ontario.” If you choose this route, be sure to provide your location (not just hardiness zone), your soil type (clay/silt/sand/loam), details of the site (sun, exposure) and several high-resolution photos showing the plant’s overall form as well as the leaf arrangement and leaf shape. IDs obtained on social media should be checked and verified.

Is it local?

The fastest way to find out whether you’ve got an exotic or something else is to do a quick Google search with the terms [species name] and “native range”. If your plant is native to North America, check the maps that show up on Google image results.

Screenshot from CanadenSys database. — Canadensys is a national online database of plants.

Finding out whether your plant is native to Ontario is the next step. The online Database of Vascular Plants of Canada (VASCAN) is searchable by species name. Although the range maps are not detailed (province level only) VASCAN is a good place to start: https://data.canadensys.net/vascan/search?lang=en

Ontario’s Forest Gene Conservation Association (FGCA) has an excellent online resource that lists trees and shrubs (but not herbaceous plants) by eco-district. https://fgca.net/ https://fgca.net/species-conservation/native-species-learn/. The list includes information on the prevalence (common, uncommon, rare) and is organized by type (evergreen/deciduous and size (tree/shrub).

The Ontario Ministry of Natural Resources and Forestry 2018 research report (available online here: https://files.ontario.ca/ecosystems-ontario-part2-03262019.pdf) on ecodistricts is an excellent resource. Find the chapter on your ecodistrict and read about its unique plant communities. Even if your plant is not mentioned, you can learn all about your ecodistrict and its flora. Many of the plants could be great options for your garden.

screenshot from Michael Oldham's "List of the Vascular Plants of Ontario's Carolinian Zone" — This is a page from Michael Oldham’s “List of the Vascular Plants of Ontario’s Carolinian Zone”. It provides county-by-county information, as well as the Ontario “S-rank” indicator code, which denotes the frequency of occurence.

Michael Oldham’s 2019 List of the Vascular Plants of Ontario’s Carolinian Zone (Ecoregion 7E) complements the FGCA list but looks at all herbaceous plants, both introduced and native. A comprehensive scholarly report, Oldham’s list is alphabetical by species name and includes a prevalence code for each county as well as the S-rank (conservation status). The list is available here: https://www.researchgate.net/publication/317731067_List_of_the_Vascular_Plants_of_Ontario’s_Carolinian_Zone_Ecoregion_7E

For a detailed look at native shrubs, an excellent but older resource is Shrubs of Ontario by James H. Soper and Margaret Heimburger. Now in the public domain and archived by the Royal Ontario Museum, it’s available here: https://archive.org/details/shrubsofontario00sope. Another great resource is Gerry Waldron’s classic book Trees of the Carolinian Forest.

A few additional databases are included under “Resources” below but this is far from an exhaustive list. Institutions (Royal Botanical Gardens in Burlington for example) and Conservation Authorities may have their own. Checking a plant in several lists can provide insight on plants whose “nativeness” is unclear.

Suitable habitat

With a basic understanding of where your plant evolved, you can decide if it’s right for you and your garden. You may want to consider the specific environment in which the plant evolved. For example, if your home is located on a former swamp, river delta, or in a creek valley, plants that are adapted to the thin limestone soils of the Niagara Escarpment probably will not be happy there. In conventional gardening we might call this concept “right plant / right place” and try to provide a species’ preferred conditions for soil moisture, soil texture, soil pH, amount of sun or shade, and wind exposure. In the world of native plants this roughly translates to habitat. There are five major types: woodland garden; dry prairie meadow; dry alvar/rock garden, and wet meadow/rain garden. For some great southern Ontario plants listed by habitat, visit the Ontario Plant Restoration Alliance website: http://www.opra.ca/plant-features.html

Be sure to consider your larger surroundings. If your property is adjacent to a conservation area or forest, you may decide to plant only those species that are native within a radius of a hundred kilometers or so. If you live in the middle of a large urban centre there’s less need for concern.

photo of Eutrochium purpureum — Spotted Joe Pye Weed Eutrochium purpureum aka Eutrochium purpureum subsp. maculatum. Image credit: Sarah A. White, Clemson University

photo of Eutrochium dubium 'Little Joe' — Eutrochium dubium is a species of Joe Pye weed native to the East Coast of North America. In Canada it is found only in Nova Scotia. This species’ mature height is only about 4′– ‘Little Joe’ is one of the many named varieties.

If you have existing, low-functioning nativars (cultivars of native plants) consider removing them gradually. Perhaps you planted the right genus but the wrong species—for example Eutrochium dubium ‘Little Joe’ instead of an Ontario native Joe Pye species. Your thriving patch of Penstemon digitalis ‘Dark Towers’ can stay until your seed-grown Penstemon hirsutus is ready. As your gardening journey continues, don’t let it turn into a joy-spoiling quest for perfection. Your garden can teach, inspire, and guide, if you give it time and attention. Seeing native plants bring life to your garden will boost your momentum and interest but, ultimately, you get to decide when your garden is native enough.