Some like it hot

David Chapman takes a look at wildflowers that can survive long periods of warm, dry weather…

Sea kale, seen here at Penmon Point, Anglesey, can grow on shingle

While last year’s long, dry summer meant we could plan outdoor events confident in the knowledge they wouldn’t be rained off, the water shortage did cause difficulties in some of our natural habitats. Indeed, I lost several plants in my garden – which made me consider which wildflowers can (and can’t) cope with drought, and why.

Some plants have adapted to cope with dry conditions. You’ll find them on sandy or stony ground where rainwater quickly drains away, as well as by the coast, where wind and salt spray create desiccating conditions. And, while it might seem counter-intuitive, many mountain-top plants have also had to adapt to drought – there might be plenty of precipitation up there but it is frozen for much of the year, while the effect of strong winds is much more severe at altitude.

Adaptations, which can seem incredibly clever, have occurred over many thousands of years and allowed certain flowers to colonise difficult terrain. Let’s take a look at some of them...

Blue is the colour

Viper’s-bugloss (or snakeflower) is a biennial, usually found growing on sandy or stony ground. It has a long flowering season and boasts beautiful blue, bugle-shaped flowers which are incredibly valuable to a range of pollinating insects – especially bumblebees. The flowers have protruding red stamens which have been likened to vipers’ tongues (hence the plant’s name). In order to grow on sand, the viper’s-bugloss has developed bristly leaves and stems. The bristles reduce the movement of air over the surface of the leaf and cut out some of the sun’s heat, combining to reduce transpiration – the loss of water through the plant’s stomates (pores), a process which could be compared to human sweating. 

Viper’s-bugloss also has a long ‘taproot’ which can collect water from deep down in the soil. A taproot is essentially a broad, tapering root that grows straight down into the ground, and from which finer subsidiary root systems grow. The most familiar taproot belongs to the carrot – we eat it! Good examples of wildflowers with taproots include wild carrot and dandelion.

Sea kale, mullein, yellow-horned poppy and sea holly also all have taproots but their leaves have also adapted in different ways. Mullein has very furry leaves which reduce air movement and transpiration. Sea kale, yellow-horned poppy and sea holly have light-coloured leaves which reflect light and heat, reducing water loss. Other plants have glossy or waxy leaves for the same purpose. 

Reducing water loss by leaf adaptation has been employed by most mountain-top plants, or ‘alpines’. They tend to have very small leaves and also sport a low-profile which helps them to hide in sheltered spots, where the wind doesn’t dry them out quite as quickly. Mossy saxifrage and moss campion are just two examples. 

Many of the herbs we grow in our gardens – such as rosemary, thyme, oregano, lavender and fennel – have a Mediterranean origin and sport small leaves that make them suitable for dry summers.

Both thrift and mountain avens, which grow on mountains as well as on rocks by the sea, have adapted leaves. Thrift has very narrow, needle-shaped leaves with few stomates; mountain avens have larger leaves but theirs are tough and leathery. Typical of alpines, they both grow low to the ground to avoid the wind. Thrift creates its own mounds of compost by growing on itself year after year. Meanwhile, heathers, which often grow on mountains, have very small leaves featuring a thick cuticle (extra-cellular membrane) and sunken stomates.

Water wonders

Some plants have even developed strategies for storing water – the best known of these, of course, being cacti. Although Britain isn’t hot enough for wild cacti, we do have other ‘succulents’. Stonecrops have succulent stems and leaves to store water and a thick, waxy cuticle to cut down on water loss.

However, having leaves that are nice and juicy can make plants vulnerable to slugs and snails – navelworts which grow in our garden wall are a prime target.

To counteract this, some plants, such as spurges, store water more cunningly. These plants retain water as a white sap within their stems. This sap is irritating or even poisonous which encourages animals to look elsewhere for their lunch. 

Other plants alter their shape during the day to cope with hot weather. For example, as the sun rises and the temperature increases, marram grass will gradually roll itself up to hide away most of its stomates. Other plants will turn their leaves on edge to avoid excessive heat and those that can’t, might wilt. Wilting may seem like the end of the road for a plant – but it temporarily  reduces the leaf area impacted by the sun. Plants will recover from a wilt, often with the aid of a hosepipe or watering can.

Long-term it makes sense to try to reduce our use of water by growing more drought-resilient plants and by applying more mulch to our beds. Inspired by nature, I have made a start. I just hope that the rosemary, thyme, thrift, viper’s-bugloss and lavender I’ve planted will cope with the deluge we are likely to get this summer!

Mystery photo August 2023

Every month I will show you a photo of something from the natural world. It might be a close-up, or a subject that is difficult to identify. All you have to do is figure out what it is! Here is this month’s photo; no clues or prizes – it’s just for fun. (I will give you the answer next month, but if you can’t wait, see the digital magazine.)

The subject of July’s mystery photo was: red admiral butterfly.

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