When we look at the plants around us, we can see just how remarkably resilient some of them can be. In nature, trees take root on rocky slopes where there is barely any soil. In cities, plants emerge through cracks in sidewalks, colonize poor or disturbed soils, and establish themselves in areas that are regularly flooded. Where conditions may seem unsuitable for plant life, some species have successfully adapted and found ways to thrive.
With the tools, machinery and materials available to us, our first instinct is often to modify a site to suit the plants we want to grow. But what we perceive as a “challenging site” is not necessarily a poor location for every plant. The key may therefore be less about completely transforming a site and more about choosing species that are naturally capable of tolerating its specific constraints.
Let’s take a closer look at some of the challenging conditions that may be present on your property and explore which trees, shrubs and perennials can be good candidates for these sites.
What Is a Challenging Site?
A site can be considered challenging when some of its characteristics limit the establishment or growth of many plants. These challenges may be related to soil, water, climate or human activity. A property may have just one of these constraints or a combination of several.
Some of the most common challenging growing conditions found in Eastern Canada include:
- Compacted soil: dense, poorly aerated soil that limits water infiltration and makes it more difficult for roots to develop;
- Poor soil: low fertility, little organic matter or limited availability of nutrients;
- Dry or fast-draining soil: sandy, gravelly or rocky soils that retain little moisture;
- Heat and drought: full sun, extended periods without rainfall, proximity to surfaces such as asphalt, concrete or pavers, and urban heat islands;
- Road salt: salt accumulation in the soil or exposure to salt spray along roads, parking areas and driveways;
- Pollution and dust: particularly common near roads and in some urban environments;
- Urban conditions: limited root space, disturbed or compacted soils, heat and frequent disturbances;
- Strong winds and exposed sites: increased drying and greater exposure to harsh weather conditions.
We will now look at some of the plants known for their ability to cope with these challenging growing conditions. However, it is important to remember that a species that tolerates one particular constraint very well is not necessarily suited to all the others. The key is to identify the main challenges on your property and choose plants that are best adapted to them.
Plants for Compacted Soils
Compacted soil is dense and poorly aerated, making it more difficult for roots to grow and develop. Compaction reduces the spaces between soil particles, restricting the movement of both air and water. It can result from repeated traffic by machinery, vehicles or people and is a common challenge in clay soils, urban environments and newly developed properties.
Fortunately, some plants are better able to cope with these conditions than others. These include:
- Red Oak;
- Red Maple;
- Honey Locust;
- Balsam Poplar;
- Eastern Cottonwood;
- Ninebark;
- Balsam Fir;
- Black Willow;
- Red-osier Dogwood.
Plants for Poor Soils
Poor soil contains little organic matter or few nutrients readily available to plants. This is often the case with some sandy, gravelly, rocky or very shallow soils, as well as heavily disturbed sites where the fertile topsoil has been removed or degraded.
Poor soils can limit the growth of many plants. Fortunately, some species are naturally capable of growing in low-fertility soils. These include certain pioneer species, which can quickly colonize disturbed sites where growing conditions may be challenging. Pin Cherry is a good example.
Other plants have even more specialized adaptations. Silver Buffaloberry, Green Alder and Speckled Alder, for example, live in association with microorganisms capable of fixing atmospheric nitrogen. This relationship allows them to grow in nitrogen-poor soils and gradually contribute to soil enrichment.
Several other native species are also good choices for poor soils:
Among the introduced species that can tolerate poor soils are:
Plants for Dry Soils and Drought-Tolerant Plants
With climate change, extended periods of heat and drought are likely to become more frequent. Some species are better able to tolerate a lack of water once well established. Choosing these plants can help create more resilient landscapes while reducing the need for supplemental watering.
Some Suggested Trees and Shrubs
Perennials
- Pale Purple Coneflower
- Hairy Beard-tongue
- Grass-leaved Goldenrod
- English Lavender (an introduced species commonly grown in gardens)
Plants Adapted to Urban Conditions
Urban environments often combine several challenging growing conditions: limited root space, compacted or disturbed soils, increased heat from paved and other hard surfaces, pollution, and road salt. Plants grown in these environments therefore need to be highly adaptable. Some particularly resilient species can cope with several of these stresses, making them good choices for yards, streetscapes and other urban settings.
Trees and Shrubs That Tolerate Both Pollution and Road Salt
- Swamp White Oak
- Kentucky Coffee Tree
- Colorado Spruce
- Common Hackberry
- Russian Olive
- Shrubby Cinquefoil
Plants That Tolerate Urban Conditions and Heat
A Tolerant or Resilient Plant Is Not an Invincible Plant
Choosing a plant that is well adapted to the challenges of your site can significantly improve its chances of successful establishment and increase its longevity. However, even the most resilient species have their limits. A tree known for its drought tolerance, for example, will still need water after planting while its root system becomes established.
Young plants are particularly vulnerable during the establishment period, and the first few years are especially important. Proper watering, a layer of mulch and a few simple care practices can make all the difference.
Can You Improve a Challenging Site Before Planting?
As we have seen, even when a plant is well adapted to the challenges of a site, a few simple measures can help it become established. The goal is not to completely transform the site, but rather to reduce the most significant constraints, particularly during the first few years after planting.
- Compacted soil: loosen the soil when possible, then avoid repeated foot traffic or the passage of vehicles and machinery around the plants.
- Poor soil: adding organic matter can be beneficial in some situations. However, avoid trying to compensate for poor soil with excessive fertilization, particularly when choosing species that are naturally adapted to low-fertility soils.
- Dry soil: apply mulch to reduce evaporation and help retain soil moisture. Even species known for their drought tolerance need adequate watering during the establishment period.
- Road salt: whenever possible, plant away from areas directly exposed to salty spray and piles of salt-laden snow. Good drainage can also help leach accumulated salts from the soil.
- Urban environments: provide as much soil volume as possible to allow roots to develop. Minimize soil compaction and, whenever possible, plant away from hard surfaces that absorb and reflect significant amounts of heat.
Work With Your Site Conditions Rather Than Against Them
Careful monitoring, adequate watering and good planting practices remain essential. By choosing species suited to the existing growing conditions rather than trying to completely transform the site, you can improve your chances of creating a more resilient and sustainable landscape.
Choosing the right species allows you to work with your site conditions rather than constantly fighting against them.
Article written by Suzanne Simard, horticultural writer and horticultural technologist, and Audrey Rondeau, Biol., M. Env., Production and Development Director at Pépinière Vert Forêt, with AI-assisted editorial support.
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