Emma Lewis

wildflowers represent nature’s optimum; natural selection occurring over many generations has promoted the traits that give the best chance of survival.

Wildflowers appear to be very much in fashion this season, with many of the designers at RHS Chelsea choosing to embrace both naturalistic planting schemes and wildflowers in their show gardens. Although wildflowers have previously been selected to complement or provide an attractive alternative to cultivated garden varieties, our research now suggests they may also provide an additional benefit in the form of improved resilience to some of the effects of climate change.

Whist, the benign British climate has for centuries facilitated the cultivation of plants from around the globe, alongside a wide selection of their derived cultivars, this may become ever more difficult as climate change triggers increasingly extreme weather. The traditional garden lawn has been well documented as a potential casualty of climatic change but the fate of many popular bedding plants, perennials and shrubs has also been called into question. With the UK expected to face more frequent bouts of both flooding and drought, there is a need to identify plant types that are capable of withstanding these opposing stresses, and this is what my research aims to address.

Over the past two years, I, supported by the Royal Horticultural Society, have been looking at some of the factors that influence a plant’s resilience and how we can use this information to make our gardens more robust with respect to climate change. Primarily I have been focusing on the effect of cultivation. Cultivation represents a complex evolutionary process, where artificial selection is used to promote and enhance particular traits that we value. Through this process we have been able to develop the huge selection of cultivated varieties (or cultivars) that are available to us today – but what effect does this process have on plant resilience?

Survival of the fittest

Essentially wildflowers represent nature’s optimum; natural selection occurring over many generations has promoted the traits that give the best chance of survival. This means that at any given time the individual plants that survive and reproduce are those best suited to the current conditions. Therefore we might expect that deviating away from this evolutionary optimum to develop; for example, a more floriferous or compact variety is likely to reduce the resilience of this new cultivar relative to its wild parent. Consequently, it might also be expected that the further we deviate from the wild parent the greater the reduction in resilience.

To test this theory we have been running a series of experiments mainly using the common primrose (Primula vulgaris) and three of its cultivated varieties. The varieties represent a scale of cultivation, which is assessed visually; so that the first variety ‘Cottage Cream’ typically flowers more reliably than the wild type but visually they appear very similar (and is actually sold in some supermarkets and hardware stores as the wild type!), where as the second and third varieties represent more of a typical bedding plant with ‘Alaska’ producing fewer but much larger flowers, and ‘Forza’ producing many medium sized bicoloured flowers.

So far from these experiments we have learnt that cultivation does seem to play a significant role in determining plant resilience, with the wild primrose and ‘Cottage cream’ performing far better than the two more cultivated varieties across all the stress tests.

Interestingly we have found the more cultivated varieties appear to succumb to stress more quickly than the wild type. This might be due to the fact that cultivars are typically driven to produce flowers regardless of the environmental conditions they find themselves in. They push a greater proportion of their resources into flower production, leaving fewer resources available for roots and shoots. This reduced flexibility in their growth response means they are less able to adapt to stress when it arises and are less likely to survive as a consequence. We also found that the more highly cultivated varieties are less able to bounce back after periods of extreme stress, so when the wild type and ‘Cottage cream’ were able to produce new leaves and start growing again during periods of recovery, the two cultivated varieties continued to decline.

So what does this mean in the context of a garden? Essentially, this trend for wildflowers, potentially including wildflowers from other parts of the globe, may well be good news for those of us looking to build greater resilience into our gardens. If you want a low input garden that will cope with the stresses and strains of climate change you may wish to step back from the highly-flamboyant flowers and unusual foliage, and instead embrace wild varieties or those cultivars that closely resemble their wild parent. These plants are more likely to tolerate a broad range of stresses and perform aesthetically, however it is also important to note that many of these types produce far less impressive floral displays. Conversely if you are still striving for a garden full of highly cultivated show-stopping plants, you might find yourself spending ever more time trying to buffer these beautiful but delicate varieties from the increasingly turbulent weather. Nevertheless, the opportunity to grow the ‘downright difficult’ or even the ‘near impossible’ has always appealed to some gardeners, and is likely to continue to do so in the future!

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