Climate change plants: extreme
Dr Eleanor Webster suggests plants that can survive wet winters and summer drought
The nature of gardening means that we are all in tune with the weather, noticing an extended growing season as temperatures rise, and the challenges presented by late frosts and heavy rain. What we are observing is the response of plants to our changing climate, a topic which is explored further in the Gardening in a Changing Climate report I recently co-authored, published by the RHS.
The report summarises published climate projections, which suggest that the UK will become warmer, with wetter winters and drier summers. It also highlights one of the biggest challenges for gardeners in coping with weather extremes, as rainfall becomes increasingly concentrated into heavy, intense downpours, followed by prolonged periods of dryness.
As a result, in order to ensure a garden fit for the future, planting schemes should focus on resilience. We will need to consider which plants will stand up to extreme conditions, while still delivering on aesthetics such as colour and structure.
Adding height & colour
To achieve height relatively quickly, Sambucus nigra f. porphyrophylla is a great choice. The attractive lacy effect of the leaves is particularly adept at intercepting rainfall before it reaches ground level, thereby reducing waterlogging. Growing up to 3m in around five years, this deciduous shrub offers colour throughout the growing season with rich purple foliage complemented by tiny pink flowers with an elderflower scent in the summer. While happy in almost any soil, this species prefers full sun or partial shade.
Adding a little more height and spread but offering a similar colour scheme, Cotinus coggygria ‘Royal Purple’ can grow to 8m in height in most soil types and aspects. Reaching maximal growth can take over 10 years, so this is a long-term investment. While slow growing, C. coggygria has been found to withstand strong winds and is therefore a good alternative to large trees in exposed sites. This species will also help regulate soil moisture due to an efficient mechanism for transporting water from the soil to the air following heavy rainfall, while using minimal water when the soil starts to dry.
For a pallet of reds, oranges and pinks, try Amelanchier x grandiflora ‘Robin Hill’. Pink flowers in spring give way to purple berries in summer before a display of oranges and reds in autumn. As a small, upright deciduous tree, this species is resilient to strong winds making an effective hedge or screen if required. Despite preferring sandy soils, ‘Robin Hill’ can tolerate wet and dry conditions, providing the soil is not too alkaline.
A good option for shady spots, Viburnum opulus ‘Roseum’ is a stunning bushy deciduous shrub that can tolerate wet soils following a rainstorm. Fragrant white or pink flowers throughout the spring and summer are followed by red, blue or black berries coupled with rich red leaves in the autumn. Requiring minimal maintenance, this shrub is suited to most soils, aspects and exposures.
Versatility & resilience
For a striking herbaceous perennial, try Primula vialii. With a conical spike of red and violet adding interest in the spring, this species can tolerate both waterlogged and dry environments providing that the latter does not persist for more than a week or two. Limited to acidic, loam soils, P. vialii can be a great addition to a boggy area of your garden, or in the depression of a rain garden.
Recent research at the University of Reading and University of Sheffield has shown Stachys byzantina to be resilient to flooding that lasts for a few days such as following a heavy downpour, making this species an ideal option for sunny, southwest facing slopes, flower beds or cottage gardens. The evergreen silver-coloured leaves and maximal height of 40cm make S. byzantina a great option for ground cover, and its purple whorls that delight in summer are an added bonus.
Tolerating most soils and happy in wet or dry conditions, Verbena bonariensis is incredibly versatile providing waterlogged conditions are not prolonged for more than a few weeks. Requiring a sunny spot, V. bonariensis boasts purple flowers throughout summer and autumn and its upright stature offers rapid height, growing up to 2m in just three years but only spreading to 0.5m, making this an ideal choice for smaller spaces. Oblong leaves offer unobtrusive foliage from spring to autumn, and the sparse density of leaves helps to maintain good air circulation in herbaceous borders following heavy summer downpours.
The red stems of Cornus alba ‘Sibirica’ offer striking winter colour and structure, perfect for low maintenance borders and adding brightness during the winter. Another advantage of this species is its hardiness, being particularly tolerant of intermittent drying and wetting, but it does prefer a sunny spot.
Year-round interest Calamagrostis brachytricha is a particularly versatile grass, and was chosen because of its ability to tolerate most soils, aspects and, most importantly, those intermittent wet and dry periods. This species offers evolving interest throughout the year: green foliage in spring and narrow, fluffy, purple-tinged plume-like sprays of flowers in summer and autumn when leaves also turn a rich golden orange. Bushy and tall in stature, this grass will be an excellent addition to both informal and formal planting regimes.