Hot and bothered
Val looks at how climate change affects plants and insects
ITHINK most gardeners realise that our climate is changing, and the statistics back this up. Weather records show that 2019’s average temperature was 1.1°C above the longterm averages recorded between 1961 and 1990. The UK summer of 2018 (June, July and August), was the joint hottest on record since 1884. The 1990s was the warmest decade in Central England since records began in the 1660s.
The climate has changed in my lifetime. When I was a child in the 1950s, living in suburban London, we always had frosts in September. Autumn would be a season of chilly mornings, so you needed a coat and long socks. More urban buildings have increased temperatures, and now frost, if it happens at all in London, is more of a rarity.
This means that the growing season is longer, with the French beans we sowed in early August usually cropping until October as long as they’re fleeced on cold nights. And some plants are not flowering when they used to. I used to think of the herbaceous perennial Clematis heracleifolia as being a September jewel, but now it’s out in July.
The buddleja bush now produces its flowers in July, rather than August, before the emergence of larger butterflies like the peacock, red admiral and small tortoiseshell. I’ve started to cut mine back harder in an attempt to delay the flowers. This year I had an autumn-flowering snowdrop out in the middle of September – six weeks earlier than usual. It’s evidence that warmer temperatures are making some plants precocious.
Summers are hotter and the longer hot spells are making the soil drier. This is slowing up some flowers. My autumnflowering asters, perennial sunflowers and goldenrod don’t do much until the second half of September after dews have refreshed them. And the flowers are not as luscious as they used to be.
Warmer temperatures mean we often see late-flying insects in the garden. The hummingbird hawk-moth has been seen here on the last day of October, nectaring on valerian flowers and hardy salvias. We’ve seen small copper butterflies, too, and they have a taste for goldenrod. We grow the goldenrod Solidago rugosa ‘Fireworks’ and I always intend to cull the clump every year, until it flowers and then I relent because it’s covered in insects for six to eight weeks. Lean into it and it’s sweetly scented.
The small copper butterfly (Lycaena phlaeas) adores the yellow flowers. These fiery, fast-flying small butterflies only appear in warm weather, so higher temperatures may help them, although you normally see only one or two at a time. There can be three broods in warmer summers and we’ve seen some in April and in autumn this year. The main August brood failed to materialise here due to unseasonable wet weather.
The small copper, which is a haymeadow or short-grassland species, is still considered common. However, intensive farming, the demise of rabbits caused by myxomatosis and less sheepgrazed pasture has had a knock-on effect. The main caterpillar food plants are common sorrel (Rumex acetosa) and sheep’s sorrel (R. acetosella).
Some butterflies have been badly affected by warmer temperatures, including the once common wall brown (Lasiommata megera). Several of these butterflies used to bask on the walls of my house in the 1990s. I would see them doing this throughout summer and I never imagined it would become such a rarity in the heart of England.
The problem has arisen because the wall brown has been lulled into producing a late third brood due to the higher temperatures in the heart of England. This generation perishes before the caterpillars can pupate and overwinter. I had to go to the Pembrokeshire coast, where maritime climate prevents extremes of temperature, to see it again.