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 its 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 for poor, thin soils in baking sun.

What is being overlaid now is how plants cope with our changing climate. Here in the UK, we have 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, 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, they 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.

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 others to withstand changing temperatures and rainfall patterns. For instance, many Salvias are borderline annuals and many Agapanthus need protection in regular winters.

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

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. 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 root ball to the elements, surrounded by a smaller layer of soil and compost than in the ground. 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 frost can 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.

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 wind-rock. Wind-rock, in turn, can lead to water penetrating the root ball in winter and freezing at the heart of the plant, often with devastating consequences.

So, a very simplistic answer might be – if a plant survived last summer and last winter, 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.

Claire Mitchell is 'The Garden Editor', a well respected horticulturist based in Overton. She also has worked with us at the nursery on Wednesdays during the Summer. Claire has a background in sustainability and led the legal team of the UK Government on renewable energy and climate change . She is also a trustee of the Chartered Institute of Horticulture. To view her website click on the following link Sustainable Gardening | The Garden Editor | Overton

RHS Hardiness ratings