Drought-tolerant planting is everywhere at the moment. Open a gardening magazine, visit a flower show or spend ten minutes looking at garden design online and you'll probably encounter the same advice: our summers are getting hotter and drier, so we need to start planting gardens with drought-tolerant plants.
Broadly, I agree. But there's a problem. We live in the North West of England. Surviving a hot, dry spell in July is only half the job. The same plant might then have to survive five months with its roots sitting in cold, wet soil. That's where things get rather more complicated.
Drought Tolerant Doesn't Mean Indestructible
There are some wonderful plants associated with dry conditions. Lavender, rosemary, Cistus, Santolina, Perovskia – now Salvia yangii – and many Mediterranean-type plants immediately spring to mind. They're attractive, often fantastic for pollinators and can cope extremely well with limited summer rainfall once established, so understandably we're being encouraged to plant more of them.
But look at where many of these plants originate and there's an important difference. They may experience dry summers. What they don't necessarily experience is a Lancashire winter in heavy clay. Cold is one thing; cold and permanently wet roots can be quite another.
Sometimes It Isn't Winter That Kills a Plant. It's the Drainage.
I've seen plants described as perfectly hardy fail over winter, and the immediate assumption is usually that it got too cold. Sometimes it did, but often I suspect the real problem is happening underground.
Roots need oxygen. If soil becomes saturated for extended periods, the spaces that would normally contain air fill with water. Some plants tolerate that remarkably well; others don't. Simply looking at the minimum temperature a plant can tolerate therefore doesn't tell us whether it's suitable for a particular garden. We also need to know what happens beneath our feet.
This Is Why I Don't Like Designing Gardens From Plant Lists
There are endless lists online: 10 Best Plants for Drought, 20 Plants for a Changing Climate, Mediterranean Plants for British Gardens. They're useful for ideas, but they can't see your garden.
They don't know whether you've got free-draining sandy soil or clay that sticks to your boots in November. They don't know whether the garden sits on a slope, whether water from the surrounding properties drains through it, or whether that sunny border in July becomes a sump in January. Those things matter considerably more than whether a plant appears on somebody's list of drought-tolerant species.
We Actually Need Plants That Can Cope With Both Extremes
This, I think, is where the conversation around climate-resilient planting needs to become more interesting. We're not simply designing for drought; we're designing for variability.
A garden might experience weeks with very little rain during summer, followed by prolonged periods of saturated ground during winter. The really valuable plants therefore aren't necessarily those that tolerate the driest conditions. They're the ones that can tolerate a reasonably wide range of conditions. That's a much harder plant list to create, but it's also a much more useful one.
Soil Might Be More Important Than the Plant
Before changing the planting palette completely, perhaps we should spend more time thinking about soil. It's not particularly glamorous. A photograph of soil structure isn't going to get quite the same attention as a beautifully planted Mediterranean border, but if the soil doesn't work, neither will the planting.
Sometimes we need to improve drainage. Sometimes organic matter will help improve soil structure. Sometimes we need to reduce compaction caused during construction, and sometimes the answer is creating raised planting areas. Occasionally, the correct answer is to stop fighting the site altogether and choose plants that actually enjoy the conditions we've got.
I think that's an important part of good garden design: don't automatically change the garden to suit the plant. Sometimes change the plant to suit the garden.
Gravel Doesn't Magically Create a Mediterranean Garden
This is another one that bothers me slightly. Putting gravel around lavender doesn't suddenly give it Mediterranean growing conditions. The soil underneath is still the soil underneath.
A layer of decorative gravel can look fantastic and perform useful functions, but if there's 400mm of compacted wet clay beneath it, the plant hasn't suddenly moved to Provence. The construction beneath the planting matters, and that's something photographs rarely show.
Newly Planted Isn't Drought Tolerant
This is perhaps one of the most important points. A drought-tolerant plant still needs water when it's establishing. So does a drought-tolerant tree.
We sometimes talk about plants being drought tolerant as though they can be planted in June, watered once and left to fend for themselves. They can't. Until a plant has developed a root system capable of accessing sufficient moisture from the surrounding soil, we're responsible for supplying it.
Depending upon the plant, soil and weather, establishment can take considerably longer than people expect. Drought tolerance is generally something we benefit from after establishment, not something that removes the need for establishment.
Trees Change the Equation Completely
If we're serious about designing gardens for hotter summers, I think trees deserve far more attention. We tend to concentrate on finding drought-tolerant shrubs and perennials, but one of the most effective ways of making a garden more comfortable during hot weather is to create shade.
A well-positioned tree can shade paving, seating areas and parts of the house while also changing the growing conditions beneath and around it. As the tree matures, the garden develops its own microclimate. Soil is shaded from direct sun, evaporation can be reduced and plants that might struggle in an exposed position can perform very differently.
Of course, trees have to be selected just as carefully as everything else. Soil, ultimate size, proximity to buildings, exposure and available rooting space all matter. But if we're discussing how gardens need to adapt to hotter summers, simply producing longer lists of drought-tolerant perennials seems to miss one of the most useful tools available to us.
Perhaps ‘Climate Resilient’ Is a Better Description
The more I think about it, the less useful the phrase “drought tolerant” becomes when considered in isolation. What we really need are climate-resilient gardens.
That means thinking about drought, but also intense rainfall, saturated winter soils, drainage, wind, occasional cold weather and the increasingly unpredictable transitions between them. It means choosing plants that can cope with the conditions they're actually going to experience rather than the conditions portrayed in a photograph.
For gardens in the North West, resilience may be far more important than simply drought tolerance.
Our Gardens Don't Need to Look Like Southern Spain
There's another danger in all of this. In responding to predictions of hotter, drier summers, we can easily begin designing every garden as though it's somewhere considerably further south.
There's nothing wrong with Mediterranean-inspired planting where the conditions and design suit it. But North West England has its own landscape, climate and horticultural character. We don't need to abandon that simply because summers may become hotter or periods without rainfall become longer.
The objective should be to create gardens capable of adapting to changing conditions while still belonging to the places they're built.
Design for the Conditions You've Actually Got
Perhaps that's ultimately the point. Garden design has always involved responding to a site. Climate change makes that more important, not less.
We should absolutely think about how plants will cope with hotter and potentially drier summers. But we should think just as carefully about what happens when autumn arrives, the rain starts and that same soil remains wet for weeks at a time.
Because in the North West, the challenge isn't simply finding plants capable of surviving drought. It's creating gardens capable of coping with both ends of the weather forecast.
Don't design a garden for the weather you want. Design it for the conditions it's actually going to experience.