In this blog Herne Hill Tree Watch is doing a little bit of amateur phenology. That's the science of changes that plants and animals undergo from season to season, and how they're affected by factors like the climate. Thousands of citizen scientists across the record events like when trees flower, frogs spawn and birds migrate, and the data is used by professional researchers.
We chose to note down the rough dates, between mid-February and the end of April, when some of our familiar trees blossomed this spring, not as part of any big project but only to give us a benchmark that we might use in future to measure the impact of global heating. If you're interested in doing some phenology yourself you might want to start here.
A few caveats before we begin. First, we use the term 'blossom' a bit loosely. In strict botanical terms, the word only applies to the flowers of trees that bear 'stone fruits', which have a single hard pit or seed inside the flesh. That covers cherries, plums, apricots, peaches and nectarines, as well as almonds, but rules out, for example, apples and pears. They aren't stone fruit, they're 'pomes', with multiple seeds or pips at their core. But what else would you call the gorgeous pink and white flowers that everyone recognises as 'apple blossom'?
Second, we don't aim to cover every tree species in the area, just the most beautiful, the most interesting and the most familiar. And third, this hasn't been a great spring for long days of sunshine so some of the images will look a bit dark and gloomy. If you find any photos like that just use your imagination!
FEBRUARY: cherry plums
The first blossom of 2024, like every other year, belonged to the ever-reliable cherry plums (Prunus cerasifera). By February 19, still officially wintertime, the big purple-leaved cherry plum (Prunus cerasifera 'Pissardii') at 19 Beckwith Road, pictured below left at twilight, was already fully clothed in small white flowers. Over on Burbage Road, outside no. 8, the bright pink blossoms of the black cherry plum (Prunus cerasifera 'Nigra') were only just emerging from their buds and the branches were still lightly clad. But they were a welcome splash of colour after a long, grey winter.
Two and a half weeks later, on March 8, helped by some welcome sunshine, the Burbage tree was richly decorated in pink, and so were its young cousins at the top end of Elfindale Road, at no. 1 (pictured) and no. 15. It's good to see these two doing well, since the cherry plum population in Herne Hill has been dwindling in recent years as older trees have succumbed to disease, decay and storm damage. In fact the tree outside 1 Elfindale was only planted two years ago as a direct replacement for one brought down in Storm Eunice in February 2022. The cherry plum at no. 15 arrived during the previous season.
At this point we should have a few words about the Latin names. The genus Prunus covers all the familiar supermarket stone fruits: cherries, plums, apricots, peaches and nectarines, as well as almonds; and the species cerasifera means 'bearing cherry-like fruits'. As for the cultivars - the features introduced by breeders - 'Pissardii' derives from Ernest François Pissard, the Shah of Persia's head gardener, who first grew the tree in 1880. And the pink cherry plum was called 'black' ('Nigra') because of the blackish-purple leaves and stems.
The English name for the species, cherry plum, also needs a bit of explaining. It's definitely a plum tree, not a cherry, and is in fact an ancestor of our domestic plum (Prunus domestica). Its red, or sometimes yellow, fruits, some 2.5 cm across, are 'cherry-like' not just in their appearance: you can eat them, either straight off the tree or made into jam.
FEBRUARY: Magnolias
By February 19, the magnificent magnolias of Casino Avenue were ready to burst on to the stage. The furry flower buds were all swollen and a few were starting to reveal the tips of their wine red petals.
A return visit on March 9 showed the Magnolia 'Galaxy' at 104-106 Casino in its pomp.
There are now 27 magnolias on this single street, including 10 planted since 2021. The white flowers tend to be smaller than the pinks, and more readily blown away by the wind. The white one in the photo below is probably a 'Merrill' cultivar, but there are also some Magnolia kobus (the northern Japanese magnolia that we featured in October 2021) and maybe other white varieties. We need to get a magnolia expert to come over for the next flowering season to give us some firm IDs for the trees without labels.
Luckily for us, the contractors last year left all the nursery tags on the nine new 'Heaven Scent' magnolias on Casino. They have elegant rose pink flowers with a distinguishing red stripe on the outside of each petal - or more accurately, each 'tepal'. Magnolias are 95 million-year-old primitive tree forms so the blossoms don't have quite the same features as modern trees. The 35 species of magnolias have a botanical family, the Magnoliaceae, almost entirely to themselves apart from two tulip trees (Liriodendron).
On a less scientific note, if you can get close enough for a sniff both the 'Merrill' and the 'Heaven Scent' are supposed to be fragrant.
Magnolias have extended their reach in Herne Hill in the last couple of years, so now there are three 'Heaven Scent' in the lawns of the Hillcrest estate on Sunray Avenue, along the rear wall, and another at 32 Delawyk Crescent. Last November two northern Japanese magnolias arrived on Burbage Road, near the entrance to the velodrome, and this March we welcomed our second Southern magnolia (Magnolia grandiflora), planted at 42 Hollingbourne Road. There's an earlier one in the grounds of Pynnersmead, near the foot of Herne Hill. These evergreen trees produce enormous white flowers that open in late summer and extraordinary fruit.
EARLY MARCH Yoshino cherries
Herne Hill's signature tree, the Yoshino cherry (Prunus x yedoensis), never disappoints. The blossom that draws tree tourists to Winterbrook Road and Stradella Road every spring began to emerge on March 4 and the flowers were fully open four days later.
The little Yoshino at 63 Winterbrook, at the Stradella end of the street, is one of a batch of 10 planted just two years ago and already looked amazing.
The view along the whole length of Winterbrook was fantastic, especially when the sun shone.
A week or so later the brilliant white Yoshino blossom had turned a delicate pink. Here's the same tree at 63 Winterbrook on March 20 and a close-up of the petals at 12-14 Wyneham Road, one of four Yoshinos planted along Wyneham at the end of 2022:
You can see the change in hue in this later panorama of Winterbrook, taken on March 20.
The spectacle was all over for another year by March 23, by which time the Yoshino leaves had unfurled and the blossom had blown away.
EARLY MARCH Chanticleer pears
The fast-growing Chanticleer pears (Pyrus calleryana 'Chanticleer') that were planted on almost every street in Herne Hill in the early 2000s are also early bloomers, although much less showy than the cherries. Here's a photo of the emerging blossom at 77 Elfindale Road, taken on March 9, and one of a fully clothed Chanticleer at 19 Danecroft Road seven days later.
Wyneham Road is a great place to see pear trees in flower. It's got two Chanticleers and two related Redspire pears (Pyrus calleryana 'Redspire'): broader than their cousins, with much darker, glossier leaves and abundant blossom. The sight of the four pears and four Yoshinos all flowering at the same time on this very short street makes Wyneham well worth visiting next March.
MID-MARCH Accolade cherries
Here's a splendid tree that we've overlooked in the past: the Accolade cherry (Prunus 'Accolade'). If you're suffering withdrawal symptoms when the last Yoshino has lost its flowers, head over to 14 Elfindale Road or 54-56 Beckwith Road for a top-up of alcohol-free cherry tonic. The photos were all taken between March 13 and March 19, but one of our tree guides says 'Accolade' can even flower as early as January. And as it gets older, the blossom cover gets thicker and thicker. It's a hybrid between Sargent’s cherry (Prunus sargentii) and the winter-flowering cherry (Prunus subhirtella) and inherits their rich autumn colour too. A great choice for a small tree,
LATE MARCH Sunset Boulevard cherries
Just as the Accolade at the top end of Elfindale began to fade, two Sunset Boulevard cherries made their appearance, one at no. 6 and the other between no. 2 and Herne Hill. The tree shown below, at 6 Elfindale, was photographed on March 20. The autumn colours are good, but the real attraction is the big white flowers, each about 4 cm across. There's a total of five Sunset Boulevards in Herne Hill now: these two, planted three years ago; a third on the grass verge outside 113 Sunray Avenue, just uphill from St Faith's church, also dating from 2020/21; and another pair on Elfindale that arrived in March this year, outside 35-37 and 56-58.
LATE MARCH to EARLY APRIL Wild cherries
The blossom in the right-hand picture above belongs to one of Britain's two native cherry trees, the wild cherry or Prunus avium. There are a few wild cherries dotted around our streets, notably on Burbage Road, between the railway bridge and Half Moon Lane, and two on Hollingbourne, this one at 24-26 and the other at 62. Their flowers, pictured on March 20, are without doubt lovely, each about 2cm in diameter, half the size of the Sunset Boulevard.
For wild cherries in a more natural setting, head over to the big open space on Sunray Avenue, behind the pedestrian crossing to Casino. The two trees there were generously decked in blossom on April 7.
The wild cherry flowers hang in charming little bundles:
By the middle of April the wild cherry flowers had gone. The handsome tree at 2 Burbage, captured below on April 8, lost a lot of its blossom in Storm Kathleen, and 10 days later the trees on Sunray Green were already bearing tiny green fruit where the flowers had withered.
EARLY APRIL Quince, pear, apple
As well as the wild cherries, the big green at Sunray is home to several other edible fruit trees. The little conference pear (Pyrus communis 'Conference') in the middle and the common quince (Cydonia oblongo) along the hedge near no. 49 were both in bloom by the end of the first week in April.
One of the two apple trees planted in December 2022 was also flowering by April 7, but the other, further towards the back of the green, didn't blossom until about the 18th. We know one of this pair is a Golden Delicious eating apple (Malus domestica 'Golden Delicious') and one a Bramley cooking apple (Malus domestica 'Bramley's Seedling'), but we won't know for sure which is which until the apples themselves get big enough to distinguish.
There are also three mature apple trees on the green, pictured here in full flower on April 18. A recent pruning by our volunteers, clearing out the tangled branches, should help them return to producing fruit.
EARLY APRIL crab apples
Back on the streets, our crab apples started blossoming around the same time as the eating apples and cookers and their cheerful blossom persisted for about four weeks.
There are a couple of John Downie crabs (Malus 'John Downie') on Burbage, including this vigorous tree at no. 62, pictured on April 17. You can eat the colourful John Downie fruit when they're fully ripe, but they're very tart and best made into jam or jelly.
EARLY APRIL Kanzan cherries
Coming back to purely ornamental trees, starting from the first week of April we had a sensational display from our many shocking pink Kanzan cherries (Prunus 'Kanzan'), one of the most recognisable street trees in springtime. Burbage has eight of these incredible trees, of mixed ages, Stradella Road has four big veterans and one youngster, but Elfindale Road is mounting a serious challenge with the five Kanzans planted there in 2022.
Here is the very distinguished Kanzan quartet on Stradella, lined up very formally between nos. 77 and 97, as they appeared on April 6:
Two days later, on Elfindale, the young Kanzan on the right of the next picture, outside the car park at nos. 83-85, was confidently holding its own against the older tree over the road at no. 90:
The Kanzan below, on the pavement outside 7-14 Royston Court, Burbage Road, clearly shows the distinctive V-shape of the crown, a profile that the trees maintain into old age, like the stately specimen at 81 Stradella. Kanzans develop this characteristic polished brown bark, perforated by rings of pores, known as lenticels, that allow gases to pass in and out.
If you look at Kanzan blossom close up it seems to be bursting with energy and power. The plump double flowers bunch up in delightful bouquets or cluster in big pom-poms at the end of a branch.
Others cling to the branches to create a stunning column of blossom, like a florist's decoration for a wedding.
Let's pause for a moment to explain 'double' flowers, which look like one or more flowers tucked into another. They originated in the wild as genetic mutations, but are now produced and enhanced by horticulturists. The flowers of cultivated ornamental plants come in three versions: single, semi-double and double. Single flowers have only one layer of petals, like the Sunset Boulevard cherry we looked at earlier. Semi-double flowers have two or maybe three layers, but the reproductive parts at the centre of the flower are still visible, like they are in the Accolade cherry
And double flowers like the Kanzan are bred to have multiple levels of petals that are sometimes so profuse that the male stamens and female pistils have been modified into petals and have entirely disappeared. That means there's no nectar for insects to feed on and no pollen to transfer from flower to flower. The trees can't reproduce without intervention by plant growers and have become sterile.
MID-APRIL Double-flowered wild cherries
The wild cherry 'species tree' - plain Prunus avium, without any suffix denoting a variety or cultivar - is undeniably beautiful, especially in its natural woodland setting, where it can grow up to 30 metres high. But for glorious spectacle on a city street in April the double-flowered cultivar, Prunus avium 'Plena', which comes into bloom about three weeks later than the original, is hard to beat. The 'Plena' in the name means 'full' in Latin, signifying that the flower is full of petals.
For comparison, have a look at these images of single wild cherry crowns side by side with doubles. The first picture in the composite shows a single at 62 Hollingbourne Road on March 20 and the second a double at 47-49 Hollingbourne on April 13. The double-flowered cultivar looks much more pumped up.
Seen up close the delicate single flowers on the left, from one of the Sunray Green trees, on April 7, look timid next to the brash and showy doubles at 27 Hollingbourne, pictured on April 12.
MID-APRIL Flagpole cherries
Here's another semi-double cherry tree, the Prunus 'Amanogawa', bred for its strictly narrow habit as well as its pale pink blossom. It's known in some nurseries as the flagpole tree, and it's easy to see why. Two of these were planted on Hollingbourne Road in March this year and by the second week of April they were showing off a very satisfactory crop of flowers. The tree on the left of the picture is at nos. 39-41, its spears of flowers contrasting with the fronds of the palm in the garden in the background. The pretty blossoms on the right come from up the hill, at 7-9 Hollingbourne.
MID-APRIL Bird cherry
The last cherry on our rounds was the bird cherry (Prunus padus), the second British native after the wild cherry. Unusually for cherries, the small white flowers are crowded on to short stalks called racemes, which can each hold as many as 40. We took the picture on April 17 at 69-71 Holmdene Avenue.
MID-APRIL Whitebeams, rowans and service trees
This wide genus, Sorbus, covers many trees linked by the similarity of their flowers. Without going into technicalities, in shape and in colour the bunches of tiny flowers in springtime, perched on top of the leaves, look from a distance like little cauliflowers, where the individual florets stand proud. See if you agree.
The first local species to bloom this year was the Schouten mountain ash (Sorbus x arnoldiana 'Schouten') at 65 Ruskin Walk. Planted in December 2022, it was in flower by April 17. It's a version of the native rowan, or mountain ash, that "can tolerate the harshest of urban conditions", according to Barchams nursery. That's a good thing in Herne Hill, where almost all the previous rowans planted have failed to thrive.
Next in line was an even more recent arrival, the ascending Swedish whitebeam (Sorbus intermedia 'Brouwers') at 17 Burbage Road, which has been in the ground for just five months. It has branches that rise more steeply than the regular Swedish whitebeam and will eventually produce a pyramid-shaped tree. Its flower buds were still only part-way to opening on April 17.
Both the mountain ash (descended from a rowan, or Sorbus aucuparia) and the Swedish whitebeam are clones: essentially genetic duplicates, artificially propagated, of a particular individual tree found to have unusual but desirable attributes.
A week later than the mountain ash, the fine bastard service tree (Sorbus x thuringiaca) at 41 Casino Avenue, in the upper cul-de-sac, was in flower. The disapproving name, admittedly coined over 100 years ago, suggests this hybrid between Sorbus aria (whitebeam) and Sorbus aucuparia (rowan) was rather frowned upon at the time.
The native whitebeams themselves were the last Sorbus to blossom. The flowers on the tree below, at 66 Ruskin Walk, were hard to find but we eventually snapped some right at the top of the crown in the evening of April 30.
Next to the whitebeam picture are clusters of flowers on a very lovely rowan on the front lawn of the Methodist church hall at 155 Half Moon Lane, near the junction with Beckwith. Strictly speaking this isn't a street tree, but we're including it to show in detail the features of the typical Sorbus flower cluster. The photo was taken on April 25.
In terms of their foliage, the whitebeams have what's known as 'simple' leaves, the rowans are 'pinnate' and the rest are in between, because all Sorbus hybridise easily in the wild and in cultivation. Simple leaves are basically a single leaf on a stem. Their edges (or margins) can be lobed or toothed or parted in some other way but they're never divided into 'leaflets' (smaller leaves). Pinnate leaves, by contrast, have multiple leaflets arranged either side of a central stalk.
The leaves on the Swedish whitebeam are like those on the whitebeam, but with deep lobes around the margin. And the leaves of the bastard service tree are like the Swedish whitebeams, but with separate leaflets nearest the stalk like a rowan. You'll find all sorts of variations among Sorbus leaves as you become more familiar with them.
Whitebeam leaves are remarkable for their colouring. The surface and the underside of the leaves are both coated in long silvery hairs when they first open, giving them a light grey-green appearance. The hairs are soon shed on the topside, which turns mid-green, but they remain at the back, which stays very pale, with prominent veins.
MID- to LATE APRIL Native hawthorns
The hawthorn is commonly called the May for an obvious reason: that's when the tree traditionally is in flower. And it still is, at the time of writing in mid-May. In hedgerows, parks, woods and streets the multitudes of creamy-white flowers of the native common hawthorn (Crataegus monogyna) tumble down the tree in fragrant cascades. And unlike many other symbols of springtime, the hawthorn blossom lasts for weeks.
We first spotted the emerging flowers on April 10, on a wild bush along Greendale, and eight days later the hawthorn in the grounds of the Cassinghurst flats on Red Post Hill, near the P4 and 42 bus stop, was blooming freely.
There's a good hawthorn in flower at the end of Elmwood Road, pictured here on April 18 spilling over the railings from its home in Sunray Gardens. It's pretty big for its type, about seven or eight metres tall. And on Gallery Road in Dulwich Village, in the hedge just opposite the Dulwich Estate offices, stands this rare and beautiful pink-flowered hawthorn, spotted on April 27.
The only genuine common hawthorn street tree that we know of in the area is on Burbage Road, outside no. 94. It's a good shape for this species, which is usually tangled and scruffy. If it weren't for the odd stray branch you could say it's shaped like a cocktail glass, but that's a bit of a stretch.
There's another common hawthorn on grass at Delawyk Crescent. Go down the perimeter road opposite Ruskin Walk, past the blocks of garages and you'll see it on the right at the back of house no. 28. You'll also find a wild one at the end of Nairne Grove, by the fence to the playing fields.
The Midland hawthorn (Crataegus laevigata) is the second British native thorn. It's got similar foliage to the common hawthorn but darker and shinier. It's given rise to several popular cultivars, of which the most frequently planted is 'Paul's Scarlet', famous for its double flowers that look almost as if they're made of silk. The first picture, taken on April 18, shows a tree at 122 Casino Avenue, the second, on April 25, is of a 'Paul's Scarlet' in a garden on Ruskin Walk peeking out from behind a whitebeam at no. 66.
MID- to LATE APRIL Horse chestnuts
Our well-loved conker trees, the common horse chestnuts (Aesculus hippocastanum), are always the first big trees into leaf but by the time they blossom they're among the also-rans. The evocative white 'candles', or panicles, of flowers on this pair outside 53 Casino Avenue took until the third week of April to reach their best.
Many of our oldest horse chestnuts have been felled in recent years, usually due to the many pests and diseases that attack them, but they've been replaced by more resilient species, including red horse chestnuts (Aesculus x carnea) like the one in the left-hand photo below. You'll find it on the side lawn at Denesmead, Herne Hill, right next to St Paul's church.
Next to it is another more sustainable species, the Indian horse chestnut (Aesculus indica). We've got quite a few of these very attractive trees, at 18 Sunray Avenue, 13-15 Casino Avenue and 105 Stradella Road, but none of their bare flower spikes had blossomed by the end of April. Keep an eye out for them.
LATE APRIL to EARLY MAY Grignon's thorns and broad-leaved cockspur thorns
We've covered the rare Grignon's thorns (Crataegus x grignonensis) of Ruskin Walk a few times, including May 2022 and March 2023. The reason we keep coming back to them is their amazing berries, which hang on the tree throughout the winter. This spring there were fewer haws (the common name for hawthorn fruit) than before, perhaps because the birds were hungrier. But they still made a pretty picture amid the white blossom at no. 40 on April 25.
The broad-leaved cockspur thorn (Crataegus x prunifolia) is a genuinely four-season hawthorn, with its glossy leaves in summer, crimson berries in autumn, elegant silhouette in winter and pure white flowers in spring. But the blossom didn't appear this year by the time April came to a close, so below is the best-known prunifolia in Herne Hill on the 28th - outside 35-37 Half Moon Lane - still keeping its flowers tightly hidden.
It's the one you have to walk under if you're coming from Herne Hill station, and our volunteers recently pruned the lower branches so you don't have to duck for thorns any more. Since the council planted five of these great little trees in 2022/23 we now have a total of eight in the area.
LATE APRIL to EARLY MAY Medlars
The flowers on our two excellent common medlars (Mespilus germanica) fortunately opened up just before our end of April deadline. You might remember that the tree on the green space off Sunray Avenue, just by the zebra crossing, was planted just as the cruel summer drought and heatwave struck two years ago. It suffered badly and didn't fully recover until this spring, when the milder, wetter days encouraged its long, crinkled leaves and big white flowers, which grow up to 6 cm across. They're pretty but unpretentious.
The other medlar, growing fast between 70 Hollingbourne and 15 Warmington Road, was correctly planted six months later than its poor relative on Sunray, in December 2022, and has been generously watered by its neighbours on either side. We look forward to a good crop of fruit from both this coming autumn.
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