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What is a climate resilient plant?

Updated: Sep 20, 2023

This is based on an article I wrote for Hardy's Cottage Garden Plants Newsletter, reproduced with kind permission.

A lot of the work I do is based on the philosophy of right plant, right place. It’s so heartening to see a plant just utterly being at it’s most plant-like best when the conditions are just right for it. And that varies so much – from those plants that happily romp away in deep, moist shade, to those that crave poor, thin soils in baking sun.

Our changing climate

What is being overlaid now is how plants cope with our changing climate. Here in the UK, we have had the inauspicious privilege of breaking several long-standing climate records in the last year. We’ve had the driest February in 30 years, the wettest March in 40 years and the warmest June since records began. Overlaid with the extreme high temperatures of last summer, and the deep, penetrating cold of last winter, our plants are being put under even more pressure and stress.

Unlike humans, plants can’t walk away when a situation gets too hot, cold, wet or dry for them. They will carry on trying to live – for the desire to live is inherent in nature – but ultimately, they may just give up. Equally, the additional pressure and stress may make them more susceptible to pests, diseases or other nasty things.

Plant losses and questions

This is what gave rise to the great plant losses of spring 2023, on which I’ve written before. And so, canny gardeners are asking themselves whether a plant is “truly” hardy. That’s a question to which I think there is no simple or single answer. We know that some plants are hardier than other to withstand changing temperatures and rainfall patterns. For instance, many salvias are borderline annuals in the UK. We've also been long told to lift and store dahlias for fear of them not making it through the winter.

The RHS has a system which divides plants into temperatures at which they can survive.

But a basic temperature point for winter does not tell the complete picture. So much depends on the micro-climate in which they are planted.

Planting in pots?

Plants in containers, for example, will be far more reliant on the gardener to look after their needs. The deep freeze of last winter penetrated to the very root balls of many plants that had happily thrived in pots for years, if not decades. Plant pots effectively expose the plant and rootball to the elements, surrounded by a smaller layer of soil and

compost than in the ground.

Other micro-factors

A windier site might mean greater water loss through transpiration. The bottom of a hill can often be a frost pocket which means plants can be slower to kick start their spring growth, or even kill off blossom. While you might think the temperature in your garden

doesn’t dip below minus 5 degrees, there’s a good deal of variation between air temperature, the temperature at the top of the topsoil, and the temperature lower down.

Look after your soil

A lot also depends on the quality, depth and type of soil. More organic matter in the soil helps slow water flow off the ground which helps combat drought stress and permits nutrient take-up; and soil that roots can penetrate deeply enables greater access to ground water, and less danger of windrock. Windrock, in turn, can lead to water penetrating the rootball in winter and freezing at the heart of the plant, often with devastating consequences.

A simplistic answer?

So, a very simplistic answer might be – if a plant survived last summer's heat and last winter's cold, it’s a climate resilient plant in the place it is at present.

Keeping a close eye on what is growing well, and where, in your garden is time-consuming, but ultimately will give you a good guide rather than relying on very

broad guidelines as to hardiness. You can then expand outwards by talking to neighbours, or seeing what characteristics thriving plants share - for instance leaf shape or colour.

What's been hardy for me ?

So these are my top survivors in my garden micro-climate. How do they compare to yours?

Geraniums. Tough as old boots, and most will happily flower twice a season. There's a geranium for every place in a garden. Mine survived in borders, in pots, in half whisky barrels in both damp and dry, sunny and shady areas. Top marks.

Nepetas (catmint). I find these a good substitute for salvias in most situations, and certainly proved hardier and pulled through when Aalvia amistad and others failed. One of my favourites is Walker's Low. "Low" means "hill" in this context and is anything but short legged.

Symphotritum (asters). These late flowering daisy-like North American stars coped admirably with the heat of last summer and the pummelling of last winter. They are not in flower yet with me, but the foliage growth is good and the signs for a good show in September are there.

Roses. Need I say more? What a stunning year it's been. Makes up for that pruning in the cold.

Leucanthemum (ox-eye daisies). These are popular in wildflower meadows for a reason - with strong root systems, they have proved a willing match for the winter cold. Yes, they are possibly slightly brutish - but they are not that hard to manage.

Hellebores (Lenten or Christmas roses). These winter flowerers performed all the way through the cold and frozen winter, barely stopping to droop their flowers.

Lonicera (honeysuckle). Yes, honeysuckle can get a bit aphid-y, but that's just another reason to encourage more insects into the garden. Tough as old boots and with a lovely fragrance to boot. Cut back hard in winter.

Aquilegia (columbine, Granny's Bonnet). I don't know if it's the longish taproot these biennials form, but they had a stonker of a year last year and this year too. I imagine it's because they flower early in the season.

Lavender. I almost hesitate to include this, as I thought the winter wet wouldn't do well for them. Prostrate rosemary, which superficially is quite similar, didn't survive anywhere near as well. My lavender are on pretty poor and free-draining soil at the top of a hill, which goes again to my view that a climate resilient plant can only really be understood in the context of the micro-climate it lives in.

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