The skies are blue and the sun is shining, but it’s been a harsh spring and summer for our street trees. As we write, the Met Office is warning of extreme heat for London in the four days from August 11, although temperatures won’t quite reach the intense 40 degrees C seen on July 19. At the same time the ground is parched, with last month the driest on record in the southeast. We’ve now had well below-average rainfall since November, a crucial nine-month period when groundwater levels normally build up and young plants establish themselves.
Climate casualties
As we keep hearing, this is climate change in action, and it’s not kind to trees. If it wasn’t so hot you might think it was autumn, with parched brown leaves in the gutters and on the pavements. Some of the London planes (Platanus x hispanica) are also losing more bark than normal in reaction to heat and drought stress, like the one pictured below on Herne Hill, at the corner of Kestrel Avenue.
Four years ago a big plane on Half Moon Lane, where it meets Ruskin Avenue, lost virtually all its bark during another hot and dry July, with sheets of it peeling off and falling into the road, leaving a pale yellow skeleton behind.
The few common pear trees (Pyrus communis) in the area, on Burbage Road, Ruskin Walk and Warmington Road, have also struggled in the heat, dropping a lot of their fruit as the temperature soared. Red carpets of dried-out flesh appeared on the street below as the rock-hard, shrivelled pears fell to the ground and were crunched underfoot.
Climate survivors
Of course the most vulnerable trees in these conditions are the ones which only went into the ground in June and July, way past the recommended planting season. We gave all six of them a quick health check and most were fine, thanks to timely watering.
The American lime (Tilia americana 'Redmond') on the Delawyk Cresent perimeter road, opposite nos. 98-99, has some browning of the leaves but doesn’t seem to have lost too many. The ones remaining are still firm enough.
The common hornbeam (Carpinus betulus) opposite 105 Stradella Road is in a similar condition. Neither the hornbeam nor the lime looks any worse than when they were first planted.
On Herne Hill, at the top of Casino Avenue, the red horse chestnut (Aesculus x carnea 'Briotii') outside no. 25 also shows some browning but there are fresh new green leaves appearing, which is very encouraging.
And further down the hill, in the front lawn of the Pynnersmead flats, the Japanese pagoda tree (Sophora japonica, nowadays officially called Styphnolobium japonicum) is now doing well and looking fresh after a difficult start. Thanks are due to the staff at St Paul’s church next door who let us use their outside tap for weekly waterings.
It’s probably no coincidence that all four of these trees - the lime, hornbeam, horse chestnut and pagoda tree - are listed by the Forestry Commission’s research arm as being drought-tolerant in varying degrees. That will have to be a top priority in choosing new species to plant in the years ahead.
Over in Elmwood Road, by the junction with Wyneham Road, the tiny hibiscus (Hibiscus 'Resi') has clung on heroically. It’s dropped quite a few leaves, but the surviving ones are green. It’s still flowering and producing new flower buds.
In fact the only latecomer that’s in a poor state is the common medlar (Mespilus germanica) on the big open space on Sunray Avenue, by the pedestrian crossing. Medlars are also moderately tolerant of drought, but this one looked very unhappy from the time it was planted at the end of June. It’s a tall tree and was stressed from the outset, its leaves rapidly browning.
But now that the residents of the square are watering it regularly it’s begun to recover, with a couple of dozen fresh green leaves emerging in the crown.
Drought-resistant trees in colour
Most of our newsletter this month has been about the challenges of living with drought. But here are four drought-resistant trees that have also brought us pleasure in this hot and dry high summer.
The honey locust
The first is a species we haven’t featured before, a gleaming honey locust (Gleditsia triacanthos) at 22 Elmwood Road. This is probably the ‘Inermis’ variety, which fortunately lacks the vicious spines that the parent bears on its trunk.
It’s smaller than the species tree, which can grow to 30 metres tall, but it’s very drought-tolerant and pollution-tolerant too, making it an excellent shade tree for streets wide enough to accommodate it. The leaves are what’s called pinnate, made up of lots of tiny ‘leaflets’ arranged along a central stalk, like an ash, and the fresh growth glows bright yellowish-green, as the picture shows.
It’s not clear what the ‘locust’ in the name refers to but ‘honey’ apparently refers to the sweet pulp inside the seed pods - although you’ll rarely find these on the ‘Inermis’. The name also distinguishes it from the other locust tree, the Robinia pseudoacacia, known more frequently in the UK as the false acacia.
The false acacia also carries spines on its trunk and branches, but they’re harmless compared to the gleditsia. There aren’t any of these trees on the streets of Herne Hill but you can see a couple of big old ones along the driveway to the velodrome on Burbage Road.
Unsurprisingly, the two locusts are related. They’re both members of the pea family, or Leguminosae, trees characterised by their long pea-like seed pods, like the laburnum, the Judas tree and in fact the pagoda tree.
The pride of ‘India’
The next drought champion on our list isn’t yet a Herne Hill street tree, although we’re hoping to get three of them in the next round of planting. It’s the Koelreuteria paniculata, commonly known as the pride of India or golden rain tree (Pride of India might be a bit of a misnomer: it actually originated in China, Korea and Japan).
There is one in Sunray Gardens, though, just behind the gate next to 2 Elmwood Road, and also the one pictured here in the grounds of Judith Kerr Primary School on Half Moon Lane. You can see it in all its glory from just around the corner on Village Way, next to no. 2.
This specimen is more advanced than the Sunray tree, perhaps because it’s in a sunnier position, and its extraordinary, abundant fruit are already brightly tinted in red and amber, compared to the pale creamy-green of the more shaded tree.
These triangular, papery, lantern-like fruits are what’s officially called bladders or even inflated capsules, although neither name really does them poetic justice. Each holds a few black seeds and they last for months, turning bronze in the autumn when the pinnate leaves change to yellow and red.
Where there’s space this is a great tree and we have plans for two on Carver Road, one on each side of the street where it approaches Half Moon Lane. We’re also looking for a Pride of India at the bottom of Ruskin Walk, just south of the driveway to the garages next to no. 76.
The pagoda tree
We’re back briefly to the Sophora japonica that we mentioned above. We’ve got a growing collection of these in Herne Hill, including recent plantings on Carver Road and at Pynnersmead, but the real heartland of SE24 pagoda trees is Holmdene Avenue. There are now nine of these fine trees growing there, including two planted in May, at no. 3 and no. 18. They grow fast and give a cooling shade.
But at this time of year, in hot summers, mature trees also produce bouquets of delicate creamy-white blossom that look from a distance like lily of the valley. The tree pictured below is at 58 Holmdene.
The Persian silk tree
Finally, here’s yet another drought-proof tree with a vaguely oriental common name, the Albizia julibrissin at the opposite corner of Half Moon Lane and Village Way. It’s something of a summertime favourite of ours. The umbrella-shaped crown of mimosa-like leaves that close up in the evenings is lavishly decorated in July and August with unique, feathery, pink and white flowers that wouldn’t look out of place on an exotic coral reef. Being another member of the pea family it also bears seed pods later in the year.
This little silk tree is a bit of a fighter. It’s hardly grown in its four years in this spot, and the spindly trunk is still barely the width of a thumb. It’s no match for its big cousin on the grass verge outside the Crown and Greyhound in Dulwich Village, but it’s fair to say that the neighbouring one outside the pub, now happily flourishing, was also rather pathetic-looking just a year ago.
The silk tree bug attack
The Half Moon Lane silk tree had a bit of a health scare in June, when the still bare branches were suddenly covered with primitive-looking bugs that looked like they might finish the poor thing off. Yet within a couple of weeks they were completely gone.
It turned out that this was an infestation of brown scale (Parthenolecanium corni).
The reddish-brown, tortoise-shaped blobs you can see in the left-hand picture are the insects (or ‘scales’) themselves, females that lay up to 2,000 eggs in May-July. These hatch after a month into tiny, maggot-like ‘crawlers’ that remain under the body of the females for a short time before emerging. The crawlers then depart to feed elsewhere, leaving the dead shells of the females that you can see in the right-hand image.
If you’ve got the stomach for it, there’s a mercifully short video of crawlers wriggling out from the shell on YouTube.
How to speed up watering
Before we leave the topic of drought, here’s a simple tool to speed your watering work - especially if you’re looking after a few trees. It’s a 7-inch wide (18 cm) plastic funnel. Just put it in the slit in the green bag and you can empty your watering can really quickly without worrying about the water spilling over.
We got the idea from a short Southwark council video on Twitter. There are some other simple, helpful tips in this watering guide from Trees for Streets, the new national street tree sponsorship scheme.
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Two losses - and one gain
Finally, some good news and some bad news. The bad news is that we’re about to lose two trees on Ruskin Walk: a purple-leaved plum (Prunus cerasifera 'Pissardii') at no. 52 that’s succumbed to a fungal disease, and a broad-leaved cockspur thorn (Crataegus x prunifolia) at 65 that’s got nothing wrong with it but is loose in the ground and has to come down.
The ganoderma fungus in the first image is the same disease that’s hit so many cherry plums in the neighbourhood recently. These are short-lived trees but they’re popular for their pink or white spring blossom that comes out in February, before any other. The council has already planted a new cherry plum on Elfindale Road this year and we’d like to see another in this same spot on Ruskin.
The second photo shows the berries developing on the Ruskin hawthorn, and rather than see a healthy tree felled the neighbours would like to have it carefully dug up and replanted somewhere else. So the good news is that we’ve persuaded the council to cancel the original notice of removal, scheduled on or after August 5, and instead to relocate the tree to a site in Sunray Gardens.
There’s space near the flowerbed behind the swings and our co-organiser Paul and his team of volunteers from the Friends of Sunray Gardens will make sure their new hawthorn gets the best possible care.
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