NATIVE PLANT ADAPTATIONS

Smooth Sumac – Okanagan native plant

HOW ARE NATIVE PLANTS BUILT FOR FIRE?

PONDEROSA PINE (Pinus ponderosa) is one of the clearest examples of a species built for fire.

Mature ponderosas feature thick, plated, corky bark, often several centimetres deep, that insulates the living cambium beneath from the heat of a passing surface fire. The cambium layer is the growth area of the trunk which annually produces new bark and wood in response to hormones.

Pinus ponderosa lower branches self-prune as the tree matures, lifting the canopy out of reach of ground-level flames, and their needles are held in tight, moisture-retentive bundles that resist ignition compared to the fine, resinous foliage of some other conifers.

Below ground, a deep taproot anchors the tree and taps moisture other species can’t reach, letting it stand through drought as well as fire.

Ponderosa forests historically burned every decade or two in low-intensity fires that cleared underbrush without killing the big trees, which is precisely why decades of fire suppression, followed by hot, fuel-laden fire seasons like this one, can be so devastating.

Today’s fires often burn hotter and higher than the ones these trees are built to shrug off.

SMOOTH SUMAC (Rhus glabra) has broad leaves with high moisture content that lack volatile oils found in many xeric plants.

Similar to Ponderosa, Sumac also shed their lower branches as they mature, creating a separation from ground-source fuels.

Sumac spreads by rhizomes, lateral roots that send up new stems some distance from the parent plant, and after a fire top-kills the visible shrub, those root systems resprout vigorously from buds below the soil surface, often producing denser thickets than existed before the burn.

MOCK ORANGE (Philadelphus lewisii) shares this resprouting strategy. Its root crown, the tissue where stem meets root, just at or below ground level, holds dormant buds that are protected from all but the most severe fires.

When top growth is lost, Mock orange resprouts from this crown, often flowering again within a few seasons, making it a valuable presence in post-fire slope stabilization and habitat recovery.

SNOWBRUSH CEANOTHUS (Ceanothus velutinus) has perhaps the most striking relationship with fire of all. Its seeds have such hard, impermeable coats that they can lie dormant in the soil for decades and, by some estimates, over a century, waiting for a cue they may never receive without fire.

The heat of a burn, in the range of roughly 80 to 95°C, scarifies that seed coat and triggers germination, while the fire itself clears competing vegetation and leaves a nutrient-rich ash bed behind.

The result is often a dense flush of Ceanothus seedlings in the first spring after a burn, acting as a nitrogen-fixing pioneer species that helps rebuild soil fertility for the plant community that follows. Snowbrush also resprouts from its root crown, giving it a second pathway back after the flames pass.

Snowbrush Ceanothus growing after forest fire
Matt Lavin | Wikimedia Commons (CC BY-SA 2.0)

For those of us practicing and promoting xeriscaping in the Okanagan, this fire season is a hard but useful reminder of why native, drought-adapted plants belong in FireSmart landscaping conversations, not just water conservation ones.

Species like these didn’t simply survive fire by accident– they built it into their life cycles over thousands of years in our valley.

As recovery begins in the areas affected by this month’s fires, Ponderosa pine, Sumac, Mock orange, and Snowbrush are reclaiming the burned slopes, evidence of these species surviving exactly as they always have.

DIG DEEPER –
For more information, read our blog post on Fire-smart Plant Choices and our in-depth page Okanagan Heat: Helping Your Garden Thrive

The Okanagan Xeriscape Association extends its thoughts to everyone affected by this season’s wildfires, and encourages residents to consult FireSmart BC for guidance on fire-resilient landscaping around homes.

Article by Sigrie Kendrick – a master gardener and executive-director of the non-profit Okanagan Xeriscape Association.

What Okanagan Gardeners Need to Know

Garden chives

Xeriscape Plants to Watch Around Dogs

YUCCA

Few plants say “xeriscape” quite like Yucca, with its architectural rosettes of stiff, sword-like leaves and towering flower spikes. It thrives in poor, rocky soil and needs almost no supplemental water once established making it ideal for Okanagan slopes and gravel beds. Unfortunately, all parts of the plant contain something known as steroidal saponins, and ingestion can cause vomiting, diarrhea, and lethargy in dogs.
The sharp leaf tips are also a mechanical hazard for curious noses and paws.

ALLIUM

The globe-shaped blooms of ornamental Allium are one of my favourite for adding structure and pollinator interest to a xeric border, and the bulbs are remarkably drought-hardy.

But Allium species, including ornamental onion, along with garden chives and garlic, contain compounds that damage red blood cells in dogs, potentially leading to hemolytic anemia, a condition where blood cells burst within the bloodstream.

Bulbs are the most concentrated source of toxins, so dogs that dig, like mine, are at greatest risk. Symptoms may not appear for several days after ingestion, which makes it easy to miss the connection.

Bearded Iris

Bearded Iris requires minimal watering and rewards gardeners with a spectacular early-summer bloom but the entire plant is toxic.

Its rhizomes store enough moisture to shrug off dry spells but also contains irisin, a toxic compound that can cause drooling, vomiting, and diarrhea if chewed.

Most cases are mild, but dogs that make a habit of excavating garden beds should be kept away from Iris plantings.

Yews

Yew hedging is a familiar sight in Okanagan landscapes, prized for its dense, drought-tolerant evergreen structure and tolerance of poor soils and heat.

It is also one of the more dangerous plants on this list.

Nearly every part of the yew, apart from the fleshy red aril around the seed, contains taxine alkaloids that affect the heart and can be fatal in relatively small amounts.

Given how popular yew is in the Okanagan, gardeners with dogs may want to consider whether it belongs near an accessible yard, or whether a safer conifer substitute makes more sense.

Lavender

Lavender is a xeriscape mainstay for good reason. This perennial is fragrant, pollinator-friendly, and content with minimal irrigation.

Lavender contains small amounts of linalool, the consumption of which can cause vomiting, diarrhea, and lethargy in dogs.

Fortunately, most, but not all, dogs are deterred by the strong scent before they eat enough to cause a problem.

Yarrow

Yarrow, our tough, feathery-leaved native is a staple of Okanagan low-water borders.

Yarrow is only mildly toxic to dogs, typically causing vomiting, diarrhea, or excessive drooling if a significant quantity is consumed.

It’s a good example of how “toxic” covers a wide risk range, as yarrow’s risk is far lower than that of yew, but worth knowing all the same.

It should be noted that while almost all Ornamental grasses are non-toxic, Cordyline australis, often used as a centerpiece in annual plantings, is toxic to dogs.

Toxicity in plants exists on a spectrum, from mild gastrointestinal upset to genuine medical emergencies.

The dose your canine consumes matters, a dog that nibbles a leaf is in a very different situation from one that digs up and eats a bulb.

If you suspect your dog has ingested a toxic plant, contact your veterinarian immediately and try to identify the plant involved.

Creating a Dog-Friendly Xeriscape Garden

None of this means abandoning xeriscaping if you share your landscape with a dog.

It simply means being deliberate–

• Fence off higher-risk plantings,
• Choose dog-friendly xeric alternatives like Russian sage, Catmint, or Ornamental grasses for accessible areas
• Know your own dog’s habits.

GARDENING WITH NATURE

Article by Sigrie Kendrick

Good Intentions Need Good Practice

It is important to provide examples of meaningful ways to provide useful feed for pollinators such as bees.

There is no shortage of goodwill when it comes to helping pollinators. Gardeners across the Okanagan are increasingly aware that bees, butterflies, and other beneficial insects are under pressure, and many are eager to do something meaningful about it.

The question is not whether to act, but how to act effectively. When it comes to pollinator support, good intentions need to be matched with good practice, and good practice begins with understanding what pollinators actually need.

Swallowtail butterfly on Weigela

Prioritize Native Plants for Pollinators

Asters
Photo by Sigrie Kendrick

Provide Blooms Throughout the Growing Season

The Okanagan is home to a remarkable diversity of native flora that serves pollinators across the season.

Early-blooming species like Pulsatilla vulgaris (Pasque flower) and Geum
triflorum (Prairie smoke) bridge the hungry gap of early spring, offering high-quality pollen at precisely the moment when emerging queen bumblebees and solitary bees need it most.

As the season progresses, plants like Balsamorhiza sagittata (Arrowleaf balsamroot) and Penstemon species carry the load through late spring and early summer by supporting both generalist and specialist bee species.

Mid-season support can come from Gaillardia aristata (Blanket flower), and Linum lewissi (Blue flax).

Later-season bloomers such as Monarda fistulosa and various Asters along with Solidago (Goldenrod), are critical for bees building winter reserves.

A garden that staggers bloom times across this full season is doing far more for pollinators than any single showpiece plant ever could.

Pollinator paradise in an Okanagan garden
Photo by Judie Steeves

Think in Sequences, Not a Single Peak of Bloom

Wooly Thyme pathway
Photo by Judie Steeves

Group Plants to Make Foraging Easier

Groupings matter too. Pollinators forage more efficiently when plants are massed rather than scattered. A cluster of five Echinacea is far more useful than five individual plants of five different species dotted randomly across a bed.

When planning or replanting, think in drifts of perennials, generous sweeps of the same plant that a bee can forage systematically before moving on.

Give Pollinators Places to Nest and Overwinter

Nectar and pollen are essential, but pollinators also need places to nest, overwinter, and raise young.

Roughly 70 percent of native bee species are ground-nesters, requiring patches of bare or sparsely vegetated soil in a sunny, well-drained location.

Leaving small areas of the garden unplanted or selectively clearing mulch from a south-facing slope can make a meaningful difference.

Other species nest in hollow stems or pithy wood, so leaving dead stalks standing through winter rather than cutting them to the ground in autumn is one of the simplest and most effective habitat actions available.

Provide Water for Pollinators

Water access for pollinators is often overlooked. Consider adding a shallow dish with pebbles or marbles for bees to land on. A regularly refreshed water source adds another layer of support, particularly during the dry Okanagan summer.

Avoid Pesticides Where Possible

Have You Ever Watered a Plant…  and It Still Wilted?

Have you ever watered a plant, found the soil still damp, yet watched the leaves wilt anyway?

That plant may not be thirsty– it may be suffering from heat stress.

As Okanagan summers become hotter and heat waves last longer, gardeners are discovering that watering alone isn’t always enough. A plant also needs to be able to tolerate prolonged periods of high temperatures. And that’s where Heat Zones come in.

Rudbeckia ‘Goldsturm’ and a variety of sedum in the OXA demonstration garden during the 2023 extreme heat.  Photos by Judie Steeves

Hardiness Zones vs. Heat Zones

Most gardeners are familiar with Plant Hardiness Zones, which tell us how well a plant can survive the coldest temperatures of winter. A lack of cold hardiness in plants generally results in dramatic winter kill.

But cold isn’t the only stress a plant has to survive– summer heat leaves its own mark, just less obviously. The effects of heat stress on a plant occur at the cellular level, resulting in wilting, dieback, and flower damage. The effects often mimic drought stress but with wet soil.

Fewer people know about Heat Zones. Developed by the American Horticultural Society (AHS), Heat Zones are based on the average number of days per year when temperatures reach or exceed 30°C

While hardiness tells us whether a plant can survive winter, heat zones help us understand how well it can cope with prolonged summer heat. Plants may wilt, leaves may scorch, flowers may fade, or stems may die back– even when the soil still contains adequate moisture.

That’s because extreme heat affects how plants function, making it difficult for them to keep up with water loss during prolonged hot weather.

Plants chosen with heat tolerance in mind for the full sun setting in the UnH2O demonstration gardens

Why Heat Zones for Plants Matter in the Okanagan

That doesn’t mean every plant rated below Heat Zone 5 will suddenly fail. It does mean that heat tolerance is becoming an increasingly important consideration when choosing plants for Okanagan gardens.

How OXA Rates Heat Tolerance

Plant growers and horticultural references may provide heat zone ratings to indicate a plant’s tolerance to summer heat. Rather than asking gardeners to interpret those numerical ratings, OXA has translated them into simple, easy-to-understand categories in our Plant Database: Poor, Fair, Good, and Excellent.

These simplified ratings make it easier for Okanagan gardeners to compare plants and choose species better suited to today’s hotter summers. They are included in the Notes section for individual plants.

Every plant in OXA’s Plant Database is rated to withstand at least AHS Heat Zone 6, which gives a buffer for the Zone 5 designation.

Plants with a Poor heat-resistance rating may already struggle during our hottest summers, while those rated Fair, Good, or Excellent are generally better equipped to cope with prolonged heat.

Article prepared by Okanagan Xeriscape Association, with contributions from Mark Godlewski

Learn More

Heat tolerance is just one of many factors to consider when selecting plants. Soil conditions, exposure, irrigation, and winter hardiness all play important roles as well.

Explore OXA’s Plant Database to compare heat resistance ratings, or return to our companion guide, Okanagan Heat: Helping Your Garden Thrive, to learn more about creating climate resilient landscapes for the future.

PLANT OF THE MONTH- MAY

by Sigrie Kendrick

Bergenia cordifolia, heartleaf Bergenia

Bergenia cordifolia, commonly known as pigsqueak or heartleaf Bergenia, is a herbaceous perennial native to Russia, grown primarily as a groundcover. Practically indestructible once established, it is a foundation plant with enduring appeal.

This perennial is hardy in zones 3-8 and is tolerant of a wide range of soil types and light conditions. Reaching a height of 1 to 1 1/2 ft with an equal spread, this perennial features rosettes of large, leathery leaves, which are useful in flower arrangements.

Bergenia cordifolia blooms in April to May with dense panicles of small dark pink flowers held above the foliage by stout 16-inch stalks.

Bergenia cordifolia is not typically bothered by deer, insects or disease.

The common name of pigsqueak comes from the noise produced by rubbing the leaf between thumb and forefinger.

How does Bergenia cordifolia resist drought?

Growing tips–

Bergenia cordifolia works wonderfully for:

• shaded border fronts or rock gardens
• ground cover for woodland or shade gardens
• edging for paths and walkways
• a much-needed pop of early bloom colour
• an early nectar source for pollinators

Plant Bergenia cordifolia in part to full shade with moist, well-drained soil. It will tolerate dry shade once established and adapts well to a range of soil types.

To get the most out of Bergenia cordifolia in your garden, a protective layer of mulch is highly recommended to retain shallow moisture.

Trim back spent flowers after blooming, and remove damaged foliage in early spring to make way for fresh growth. To maintain density and vigour, divide every few years in the spring.

Suitable for use as a fresh cut flower. 

Our Plant Database features more than 500 plants tested and ideally suited for the unique challenges of gardening in the Okanagan’s extreme climate, including the plants in this article.

CLIMATE-RESILIENT PLANTS

Article by Josh Smith, Xeriscape Endemic Nursery (XEN)

Biologist Josh Smith is general manager of XEN Nursery in West Kelowna, which grows and propagates native and xeriscape plants for both ecological restoration projects and landscaping use throughout the Okanagan. He is also vice-president of the Okanagan Xeriscape Association.

Plants have evolved a range of ways to survive under a blazing summer sun.

Adaptability and climate-resilience are essential for plants native to the Okanagan Valley’s arid climate, with its hot summers and low rainfall. Increasingly, these same strategies are becoming important across British Columbia, as drought and extreme heat events intensify with climate change.

ESCAPING DROUGHT

One of the most effective tactics is simply to hide from harsh conditions altogether.

Many xeric (Latin: ‘dry’) plants “escape” drought by completing their life cycle during the moist spring months. They bloom early, set seed quickly, and then die back above ground before the heat and dryness of summer arrive.

A familiar example is Arrowleaf Balsamroot (Balsamorhiza sagittata), Kelowna’s official flower. These bright yellow blooms cover Okanagan hillsides each spring, taking advantage of abundant moisture. As summer heat intensifies, their large arrow-shaped leaves wither and dry. However, the plant persists underground, storing energy and moisture in a deep taproot, ready to sprout again with snowmelt and spring rains.

An even more dramatic example is Bitterroot (Lewisia rediviva). Growing in dry, rocky soils, bitterroot emerges early in spring to produce delicate pink flowers, often before its leaves are fully visible. Soon after blooming, the entire plant disappears from the surface, surviving the summer drought as a fleshy underground root until favourable conditions return. The Latin ‘rediviva’ means ‘revived’ and refers to this ability.

Spring bulbs follow a similar pattern. Emerging from bulbs or corms, they grow rapidly, bloom, set seed, and store energy underground before retreating as temperatures rise. During their brief time above ground, they complete their entire reproductive cycle and prepare for the following year.

Although it is much more common for plants in Mediterranean climates, some drought escapers don’t go completely dormant until next spring but simply allow leaves to dry up and yellow during the summer, then green up rapidly once the fall rains start. In the Okanagan, this strategy is used by all of our native grasses, which is why our hillsides are yellow in the summer yet green in the spring and fall.

AVOIDING DROUGHT

Some plants are able to avoid drought stress through strategies focused on maintaining a high water content inside the plant. This falls into two major categories: (i) ‘Water Savers’ prioritize minimizing water loss from the leaves, and (ii) ‘Water Spenders’ focus on maximizing water uptake from the soil.

An easily spotted water saver strategy is silvery, powdery, or fuzzy foliage. This reduces water loss by reflecting more sunlight, which lowers leaf temperature and reduces transpiration. Common Rabbit-Brush (Ericameria nauseosa), Pearly Everlasting (Anaphalis margaritacea), and Golden-Aster (Heterotheca villosa) are native Okanagan examples of silvery, powdery, or fuzzy foliage, respectively. Garden favourites like Lavender or Silver Mound also use this strategy. Though less easily identified, another water saver strategy is to reduce the quantity or diameter of the pores on the underside of leaves (stomata) to reduce water loss when the leaves exchange air with the environment.

Water spenders take a completely opposite approach and focus on getting as much water as possible out of the soil. Many Okanagan native plants produce deep and/or dense root systems to reach moisture far below the dry surface soils. Balsamroot, Common Yarrow (Achillea millefolium), and Brown-Eyed Susan (Gaillardia aristata) all produce a deep taproot and, for an extreme example, Giant Wildrye (Leymus cinereus) produces a dense fibrous root system that has been found as deep as 2.4m (8’) below ground. Garden favourites such as Missouri Evening Primrose also demonstrate this strategy well. Another water spender strategy, which is too complex to explain in this brief article, is to increase hydraulic conductance. Essentially, picture all plant roots as straws sipping at the water in the soil. Through a multitude of different mechanisms, some plants can suck harder or more efficiently on the straw than their neighbours. Saskatoon (Amelanchier alnifolia) and Antelope-Brush (Purshia tridentata) are great examples of native species with a high hydraulic conductance.

Lavender and Yarrow  (Photo by Judie Steeves)

TOLERATING DROUGHT

Finally, some plants are adapted to tolerate drought conditions directly, even when water is scarce. These adaptations can be structural, physiological, or biochemical.

Many xeric plants have narrow or finely divided leaves, reducing surface area to limit water loss and heat absorption. Desert Yellow Fleabane (Erigeron linearis) and Prairie Smoke (Geum triflorum) are examples of native species that use this strategy, and the garden favourite Pine-Needle Penstemon is another classic example. Other plants, like Snowbrush (Ceanothus velutinus), produce a thick, waxy leaf coating (cuticle) that acts as sunscreen to block some UV light from entering the leaf.

Some plants make use of accessory pigments to absorb sunlight. Chlorophyll, which is what makes plants appear green, is the most efficient pigment for absorbing sunlight, but in low-water conditions, it produces harmful compounds that can damage or kill leaves, so some plants make use of accessory pigments to shield the chlorophyll from sunlight. These pigments give off red, orange, or blue light more than green, which is why some of our drought-tolerant plants, like Oregon Grape (Berberis aquifolium), are these colours.

Another easily noticeable drought-tolerance adaptation is aromatic plants. They produce essential oils, also called volatile organic compounds (VOCs), that are often stored in glands on the leaf surface where they function to absorb and scatter excess light and form a water repelling layer to slow the diffusion of water vapour out of the leaf. VOCs also evaporate easily when heated and provide evaporative cooling, similar to sweating in animals. For native species, Big Sagebrush (Artemisia tridentata) is the most aromatic example, but many ornamental favourites also use this strategy, like Russian Sage, Lavender, Thyme, and Common Sage.

Succulents, like cacti, sedums, and sempervivums, are stereotypically thought of as some of the most drought-tolerant plants. Their almost unique adaptation is a specialized photosynthesis pathway that enables them to open their leaf pores only at night when it is cool, absorb and store carbon dioxide, and then during the day they can close their leaf pores to reduce transpiration loss and still perform photosynthesis using the stored CO2. This adaptation is highly water-efficient and is what allows succulents to have watery, fleshy leaves even in the middle of a desert.

Oregon Grape, Berberis aquifolium

Working with nature in the Okanagan

In reality, many plants use a combination of these strategies rather than relying on just one. This flexibility is what allows them to thrive in the Okanagan’s challenging climate.

For gardeners and landscapers, understanding these natural adaptations offers a powerful lesson: by choosing plants that are already suited to our environment, we can create landscapes that are both beautiful and resilient– while using far less water. As drought conditions become more common, working with nature is no longer just a good idea– it’s essential.

PLANT OF THE MONTH- APRIL

by Sigrie Kendrick

Pulsatilla vulgaris, the European Pasque flower

Few spring-blooming perennials combine delicate beauty with rugged resilience quite like Pulsatilla vulgaris, the European Pasque flower.

Named for its bloom time around Easter (Pâques in French), this silky-petalled gem is equally at home in a rock garden or a sun-baked hillside and is virtually maintenance-free.

Pasque flower is cold-hardy in zones 4-8, making it an excellent choice for even the higher elevations in our Okanagan valley.

Native to the dry chalk grasslands and limestone meadows of central and northern Europe, Pulsatilla vulgaris has evolved over millennia in some of the continent’s most unforgiving soils.

Poor, thin, and freely draining ground is exactly what it prefers. Plant it in rich, moisture-retentive soil, and it will quietly sulk or simply disappear.

Give it the lean, gritty conditions it knows, and Pulsatilla vulgaris will reward you with decades of enjoyment.

How does Pulsatilla vulgaris resist drought?

The Pasque flower’s drought resilience is structural, not incidental. Its deeply tapering taproot drives far down into rocky substrate, accessing moisture reserves long after the surface soil has dried.

The finely divided, feathery foliage is covered in soft silver hairs, a classic xerophytic adaptation that reflects intense sunlight and reduces water loss through the leaf surface.

Even the ornamental silky-tailed seed heads that follow the blooms serve a purpose by allowing the plant to complete its reproduction cycle quickly, before summer heat fully arrives.

Growing tips–

Once established, which typically takes a full growing season, Pulsatilla vulgaris requires essentially no supplemental irrigation in climates such as the Okanagan with its modest spring rainfall.

It is highly suited to xeriscaping plantings, gravel gardens, and low-maintenance perennial borders where water conservation is a priority.

Pulsatilla vulgaris prefers to be sited in a full-sun location with excellent drainage, but will tolerate part-sun.

Avoid transplanting Pulsatilla once established, as the taproot, which makes this such a successful xeric plant, resents disturbance.

Cultivars of this perennial range from the classic violet-purple through white, red, and soft pink.

Pasque flower is one of the earliest blooming spring perennials and, as such, offers vital support for pollinators emerging from the long winter.

Our Plant Database features more than 500 plants tested and ideally suited for the unique challenges of gardening in the Okanagan’s extreme climate, including the plants in this article.