Milder winters and hotter summers are changing how native plants grow, with gardens being pushed towards hardier species capable of withstanding weather extremes
Daffodils flowering before Christmas. Roses still in bloom in January. Grapes flourishing in the home counties. Across the UK, the changing climate is upending gardening calendars. But while milder temperatures mean we can now grow species that would previously be unable to endure the cold, longer growing seasons and extreme weather events are also having negative effects on the British garden.
“Generally, winters are getting milder and wetter, and the summers are getting hotter and drier,” says Mark Gush, head of environmental horticulture at the Royal Horticultural Society (RHS). This prolongs the growing season, as plants bud and flower earlier and last for longer. A 2017 report by the RHS, citing Met Office data, suggests the growing season in Central England is about a month longer on average since the period between 1961 and 1990. (The growing season refers to the extended period of time in which average daily temperatures are sustained at five degrees or higher; there is a lot of variation across the UK, with Scotland having a much shorter growing season than the south of England.)
For some plants, this can be a good thing, as they can photosynthesise for longer. For gardeners, it can also save some work: dahlia tubers, for example, which previously had to be dug up and stored over winter to avoid ground-penetrating frosts, can now often be left where they are. But some plants need a rest period, or a certain number of low-temperature “chill days” to recover before the spring.
“The fact that they’re growing a longer season gives them less time to rest,” says Tony Hall, head of arboretum, gardens and horticulture services at Royal Botanical Gardens, Kew. This could cause plants to grow weaker the following season and be more susceptible to diseases and pests. A lack of chill days can also affect fruit yield. Fruit trees such as apples, apricots and peaches all require a certain amount of downtime over winter to effectively “reset” ready to form buds, flowers and fruit the following year.
Unseasonably warm winters can also have negative effects if a cold snap comes along later. If deciduous plants (those that lose their leaves every year) such as magnolia start to flower early due to the warm, wet weather but are then hit by frost, it can kill the flowers for that year. “Once they’re hit by frost they’re hit by frost, and that’s the end of it,” Hall says. This can also have a knock-on effect on the ecosystems that depend on plants, and particularly pollinators such as honeybees, which rely on nectar so that they can build up honey stores to keep them through the winter.
Perhaps a bigger threat than the gradually changing seasons, however, is the increase in extreme weather events associated with climate change, such as droughts and floods. Gush says that good water management is critical for gardeners today. He advocates having a water butt to store water for periods of dryness, and suggests putting a mulch layer on top of soil to reduce evaporation and keep water in the soil where plants can access it.
Lawns are often more resilient than people think; Gush recommends letting a lawn grow taller in hotter weather or develop into a meadow with wildflowers (which is also good for biodiversity). “When that above-ground biomass increases, so too does the below-ground biomass,” he explains. By putting down deeper roots, the grass has access to more water, making it more resilient.
On top of climate change, flooding has been made worse in the UK, particularly in urban areas, because of an increase in impermeable surfaces such as driveways and paving. The water runs off these surfaces and can soon overload storm drains. Gush therefore advises opting for permeable paving, which allows water to get into the soil and recharge aquifers (which then help to provide water in drier periods).
In this sense, Gush says that individual gardeners can make a difference in mitigating against the effects of climate change. Another example is soil management: soil, and particularly peat, can act as a carbon sink, keeping carbon out of the atmosphere. Gardeners should therefore avoid using peat, as this is best left undisturbed in natural bogs.
One of the advantages of warmer temperatures is being able to plant more Mediterranean and even tropical species in UK gardens – Hall says palms such as the Canary Island Date Palm, pomegranates and some hardy bananas such as the species Musa basjoo can now be grown outdoors, at least in London.
But Gush warns that, ultimately, climate change will mean that we need to gravitate towards hardy species, which are capable of enduring weather extremes. “Because climate extremes are also part of the mix in terms of changing climate, there may be a number of years where there are above average temperatures and milder conditions so the plants will be able to flourish, and then there will be snap extreme cold spells, and that'll really knock them back.”
This article was first published on https://www.wired.co.uk/article/climate-change-english-garden