Plants to survive a heatwave

For some years now, gardening pundits have been telling us we may need to move towards Mediterranean climate plants in our UK gardens. But this summer has imbued that idea with a powerful sense of urgency.

Many people will have spent valuable time watering during the heatwaves, and still have lost plants. This is not sustainable. Of course, we can’t be sure that drought will be a consistent feature of the growing season in years to come, but it seems likely.

Drought-beating design

There are many techniques to counter the adverse effects of heat and drought. Installing water butts minimises the need to use mains water for irrigation. Landscaping can channel water to the plants, rather than into storm drains. Improving soil structure allows soil to hold on to water for longer, and make it available to plant roots.

Equally important will be choosing plants that can cope with the heat and lack of water. This is not quite so straightforward as it might seem, because while our summers may be becoming similar to those in a Mediterranean climate, our winters are not. Winter in the UK is still cold and damp, which doesn’t suit a lot of Mediterranean plants. We need plants that can cope with drought, and heat during summer, but also cold and wet periods.

Choosing plants for a changing climate

There are many sources of information on the conditions required for plants (such as the RHS website). But how plants grow, and what they will put up with, can vary widely from area to area (and sometimes even from garden to garden) depending on the soil and local variations in climate. You can’t beat first-hand experience on the ground.

Perennials

Ligularia – ‘Midnight Lady’ & ‘The Rocket’, plus Rodgersia

This past season has been a lesson to me in what will flourish in the sandy, dusty soil of my North Shropshire garden. Moisture-loving perennials such as Ligularia and Rodgersia were never going to like the heat. Mine are in a bog garden, but the water level of the pond that feeds it fell so low that the boggy area dried out, and the plants wilted.

Echinacea purpurea & Rudbeckia ‘Goldsturm’

I was surprised that Echinacea and Rudbeckia, which are prairie plants, needed regular watering. The RHS claim Rudbeckia came through well in their gardens (apparently it has deep roots). Perhaps mine will be better when they are more established. They also said Eupatorium (which has, I believe, been re-classified as Eutrochium) did well, though it flowered earlier. My Eupatorium only reached 60cm, flowered late, and needed regular watering. Perhaps the difference is in the soil.

Helenium (Sahin’s Early Flowerer) & Echinops

I may have despaired at the sad state of so many of the plants, but there were successes. Helenium – another prairie plant – coped well with the heatwave. Echinops, despite being big, leafy plants, were barely affected (and we had seedlings coming up all over the garden too). Verbascum and Achillea proved to be resilient, as did Verbena bonariensis. Gaura (which is now officially known as Oenothera), continued its campaign to take over the garden. Sedum (now Hylotelephium), being succulents, were able to store enough water in their leaves to get through.

Achillea millefolium ‘Lilac beauty’ (Yarrow), Hylotelephium ‘Xenon’ (Sedum) & Verbena bonariensis

Salvias, which are Mediterranean plants, were mixed. The perennial blue Salvia guaranitica ‘Blue Ensign’ would have died if I hadn’t watered it regularly, and failed to flower. But shrubby Salvia ‘Royal Bumble’ was undaunted, and has produced masses of flower from June onwards. It also survives our winters, at least so far – many salvias are not sufficiently hardy.

Salvia ‘Royal Bumble’

Iris sibirica, which is supposed to like damp soil, came through as if this year was no different to any other. It flowers early – before the heat struck – but afterwards, the leaves continued unabated. In fact, it clumped up so well I’ve recently had to divide the plants.

Iris sibirica

And last, but not least, Symphyotrichum reliably produced their tall mounds of foliage in the background, and have now erupted into bloom. They are one of my favourite perennials, and incredibly useful for a late burst of colour.

Symphyotrichum (aster)

Trees and shrubs

Most of the trees in my garden are young, and while they looked stressed at times, I didn’t see much of the ‘phantom autumn’ effects other people experienced during the heatwave.

When it comes to shrubs, Viburnum plicatum ‘Mariesii’ flowered beautifully early on, but by mid-summer was all but dead. Cornus kousa, and the purple hazels (Corylus maxima ‘Purpurea’) were hardly any better. Deciduous Berberis hardly put up a fight before their leaves shrivelled and fell (the sawflies that regularly strip them must have been very disappointed).

Viburnum plicatum f. tomentosum ‘Mariesii’ – flowering before the heatwaves

Hydrangeas are renowned for needing a lot of moisture, so it was surprising that Hydrangea ‘Limelight’ got through unscathed, and without additional water. Although it does have some shade – only getting the sun from mid-afternoon.

Hydrangea paniculata ‘Limelight’ The flowers change colour and then stay on the plant over winter. This one has produced a couple of fresh flowers in October.

Predictably, Ceanothus ‘Puget Blue’ (Californian lilac) was at home in the conditions, flowering and growing on well. Roses don’t generally like it hot and dry. Mine muddled through quite well, though they did have a long break in flowering (all except ‘Munstead Wood’, which kept on producing blooms, albeit rather slowly).

Rosa ‘Munstead Wood’

As the climate changes, our gardens need to adapt. Choosing plants that are capable not just of surviving, but thriving in the changed conditions, means we can still have beautiful, healthy gardens, without using too much of that precious resource – water.

text & images © Strelitzia Garden Design 2022

By graham

Graham Wright is a fully qualified garden designer (Post Graduate Diploma) working mostly in the North Shropshire area. Prior to becoming a designer, Graham was for many years a gardener. His design ethos is to put the emphasis on plants and sustainability.

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