GARDENING WITH NATURE

Article by Sigrie Kendrick

Xeriscape plants don’t simply survive the Okanagan’s hot, dry summers– they are uniquely adapted to thrive in them. Drought tolerance isn’t only about anatomy; it’s also about strategy.

There is a common misconception that xeriscape plants are simply tough plants–
survivors that endure poor conditions through grit alone.

The truth is far more fascinating and takes a dive into the biology of drought-tolerant plants.

The plants that thrive in the Okanagan’s hot, dry summers are not suffering through the season.

They are engineered for it, shaped by millions of years of adaptation.

Understanding what makes these plants work isn’t just interesting science but the foundation of smarter gardening in one of Canada’s most water-stressed regions.

Much of what makes a drought-tolerant plant exceptional happens where we humans can’t see it.

Blanketflower
Photo by Judie Steeves

Root Adaptations That Find Hidden Water

Root architecture is the first and perhaps most important adaptation.

Okanagan natives such as Bitterroot (Lewisia rediviva), Arrow-leaf balsamroot (Balsamorhiza sagittata), and Prairie smoke (Geum triflorum) develop stout, fleshy taproots one to three metres deep, accessing subsoil moisture that shallow-rooted ornamentals never reach.

This taproot also serves as a storage organ, stockpiling carbohydrates and water that sustain the plant through the harshest stretches of summer drought.

So efficient is this adaptation that Bitterroot, one of our region’s most iconic natives, can survive being uprooted for weeks and still revive when replanted.

Other species such as Bluebunch Wheatgrass (Pseudoroegneria spicata) and Blanketflower (Gaillardia aristata) develop dense, wide-spreading fibrous root systems that fan out through the upper soil horizon, capturing even the lightest rainfall before it can evaporate. Unlike deep taproots, these fibrous networks maximize surface area, drawing moisture from a broad swath of soil.

Xeriscape plants also invest heavily in their root systems relative to their above-ground growth. A modest-looking plant in your garden may be hiding twice its visible mass underground, allowing it to access moisture deep within the ground during the dry months of July and August heat.

Leaf Features That Reduce Water Loss

Blanketflowers in an Okanagan garden
Photo by Judie Steeves

CAM Photosynthesis: Nature’s Water-Saving Strategy

Why Xeriscape Plants Thrive in Okanagan Gardens

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.

Use Native Plants to Create a Natural Garden

Article by Josh Smith, Xeriscape Endemic Nursery (XEN)

Consider transitioning a section of your landscape to native plants, where you can reduce both maintenance and water use, conserving a vital resource in this arid valley, along with your own energy.

A side benefit is that you are providing valuable feed and habitat for all sorts of indigenous wild things– from insects to birds, to small and large mammals– by your restoration.

Do not embark on this project unless you are prepared to accept that you are collaborating with your environment, not conquering it.

Rabbitbrush, Eericameria nauseosa

WHAT ARE NATIVE PLANTS?

Native vs Endemic vs Exotic vs Naturalized vs Invasive
The scientific definition of a native species is an organism that occurs naturally in a region without human introduction, having evolved there or arrived via natural dispersion over evolutionary time.

• NATIVE plants belong here.
• ENDEMIC plants belong ONLY here.
• EXOTIC plants are introduced by humans from elsewhere.
  *NATURALIZED plants are exotic plants that behave themselves.
  *INVASIVE  plants are exotic plants that are ecologically harmful.

CONSIDERATIONS FOR CHOICES

Consider first where a plant is native— Canada, B.C., or the Interior. Winter cold, summer heat, humidity/precipitation, and competition are all factors in limiting where exactly a plant is native.

Lots of plants native to B.C. are completely inappropriate in the Okanagan, so they’re unlikely to thrive here.

Then, within the Okanagan, first you must also consider whether a plant is native to our particular region of the valley; then, in which ecoregion it belongs: upland, riparian, high elevation, etc.

Further, consider whether it would thrive on a dry silty slope, a creek edge, or in a bed of clay.

Provenance (original seed source) and site matching (right plant, right place) matter more than just choosing a native plant.

Within the Okanagan, there are extremely diverse ecosystems in close proximity to each other, and ignoring sub-regional differences can cause failure unless you are careful to plant native plants in their natural environment.

Elevation, temperature, sun exposure, drainage, and soil texture often matter more than region.

In general though:

• The South Okanagan is hot and dry and of low elevation
• The Central Okanagan is transitional
• The North Okanagan is cooler and wetter

Pre-settlement landscapes in the Okanagan featured native plants that evolved with disturbance, not with watering, fertilizer, or mulch, such as we use on our man-made landscapes. This is a fire-adapted ecosystem that consists of drought-tolerant plant communities in patchy, disturbed, open landscapes.

Many native plants expect stress and respond poorly to pampering, so, as gardeners, we should take advantage of these attributes.

Showy Milkweed, Asclepias speciosa

ADVANTAGES OF NATIVE PLANTS

LESS WATER
The use of native plants in your landscape reduces the amount of supplemental water needed, but it does not necessarily mean they require no water. All plants require enough water when first planted to help them to settle in, so at least for the first year, they are likely to need some supplemental water over the summer and during drought.

LESS MAINTENANCE
Over the longer term, inputs such as fertilizer, replanting, chemicals and other maintenance are greatly reduced with native plants grown in a natural garden. Plants that evolved here are used to our weather swings. This is their home, and they are climate-resilient.

SUPPORT LOCAL ECOSYSTEMS
Native plants also support the local ecology, including pollinators, birds, mammals, and beneficial microorganisms, as well as their companion native plants.

Native plants overwhelmingly provide better habitat than non-native ornamentals and are the entry point for energy into our local ecosystem. They are the foundation of all food webs and feed everything, or everything’s food. Birds depend on insects as part of this food web: over 95% of land-based birds in North America feed insects to their young, and this includes species of birds that exclusively eat seeds as adults.

Birds cannot survive without insects, and insects are highly-specialized and often have evolved specific digestive enzymes and life cycles that require native plants as food or as a larval host for reproduction.

For an extreme example, the Okanagan has some species of butterfly that are at risk or endangered because they have evolved to only use one specific plant, or plant family, as a larval host.

Behr’s Hairstreak Butterfly depends on Antelope Brush; Monarch Butterfly larva can only survive on Milkweeds (Showy Milkweed is the only native here), and the Mormon Metalmark Butterfly relies on Buckwheats.

Human activity and climate change have reduced the population of these plants, which results in a reduced butterfly population, which in turn reduces pollination and seed production for these plants. This type of negative feedback spiral is often the cause of species extinction.

Pollinators also require native plants. Most ornamental, non-native flowers produce nectar that can be used by native adult bees as food, but the 500-600 species of bees native to BC are often pollen specialists that require specific plants or plant families for the pollen they need to feed their larva. Although the bees are very important, flies, other insects, and birds also do their share of pollinating plants.

In addition to pollination services, these insects and birds also often provide pest control, such as being predatory on pests like aphids.

GARDENING WITH NATURE

Not all plants like the Okanagan

Popular Garden Plants That Struggle Here

Rhododendrons, azaleas, hydrangeas, and most Japanese maples (Acer species) may dominate garden centres but they’re fighting an uphill battle against this valley’s unique environmental conditions.

The most fundamental obstacle these plants face in the Okanagan is soil chemistry.

Rhododendrons, azaleas, and most hydrangeas are acid-loving plants that thrive in soils with a pH between 4.5 and 6.0. Unfortunately, Okanagan soils typically range from neutral to alkaline, often sitting between 7.0 and 8.5 pH. This alkaline environment creates a cascade of problems for acid-preferring plants.

In alkaline soils, essential nutrients become chemically bound and unavailable to plant roots, particularly iron, manganese, and zinc.

The result is chlorosis – that telltale yellowing of leaves while veins remain green – which weakens plants and makes them susceptible to other stresses.

While gardeners can attempt to acidify soil with sulphur or aluminum sulphate, maintaining the necessary pH in naturally alkaline conditions requires constant intervention and expense.

Dry Summers and Low Humidity

The Okanagan’s semi-arid climate presents another insurmountable challenge.

With annual precipitation ranging from just 250-400 mm in many areas, the region experiences genuine water scarcity.

Rhododendrons and azaleas evolved in moist, humid environments where their shallow, fibrous root systems could rely on consistent moisture and lots of organic matter. Their large, thin leaves are designed for environments with high humidity and reliable rainfall—not this valley’s dry summers and low humidity.

Hydrangeas also struggle with the Okanagan’s drought conditions. These plants require consistent soil moisture and suffer significantly when subjected to water stress, which is virtually inevitable during the valley’s hot, dry summers.

Most Japanese maples face similar challenges. These delicate trees prefer consistent moisture and protection from harsh afternoon sun and drying winds – conditions opposite to what the Okanagan typically provides.

Temperature Extremes and Wind Exposure

While the Okanagan enjoys warm summers perfect for viticulture, it also experiences significant temperature fluctuations and harsh winter conditions that stress some of these ornamental plants.

Many rhododendron and azalea varieties that appear hardy on paper struggle with this region’s combination of cold winters followed by rapid spring warm-ups, which can trigger premature budding. That can then be followed by frost damage to those tender new buds.

The valley’s frequent winds compound these problems. Strong, dry winds increase water loss from plant tissues and can physically damage the brittle branches of Japanese maples.

Rhododendrons and azaleas, with their broad evergreen leaves often lose moisture faster than their root systems can replace it.

Choosing Plants That Belong Here

Rather than fighting against the Okanagan’s natural conditions, successful valley gardeners embrace plants that thrive in alkaline soils and dry conditions.

Native and adapted plants like penstemon, lavender, yarrow, ornamental grasses, and xeric trees and shrubs provide beauty without the constant struggle.

The Okanagan’s unique climate offers opportunities to grow plants that would struggle elsewhere – Mediterranean herbs, drought-adapted perennials, and heat-loving annuals that coastal gardeners envy.

By choosing plants suited to local conditions, gardeners can create stunning landscapes that celebrate the region’s natural character while conserving precious water resources.

The key to successful Okanagan gardening isn’t forcing unsuitable plants to survive, but discovering the remarkable beauty of plants that naturally call this unique valley home.

A variety of sedums and ornamental grasses instead of coastal perennials

The relationship between plants, pests, and beneficial insects represents a natural system of checks and balances. By supporting these natural predators, we align ourselves with ecological processes refined over millions of years.

Rather than fighting against nature with chemicals and barriers, we can harness these allies to create gardens that not only produce beautiful plants but also support diverse wildlife communities.

The next time you spot a lacewing, soldier beetle, or even a spider in your garden,
consider yourself lucky to be witnessing nature’s pest control experts at work.