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Nature and Weather in South East England

The greening of the trees

Other April pages: Intro and woodland flowersVerge and field flowersBlossom and shrubsBirdsButterflies and insectsWeather

Picture: Ashridge estate. Click here for more April tree photos.

One of the most dramatic changes in the countryside in April is the return of foliage on bushes and trees. They go from a drab brown at the start of the month to glorious fresh greenery at its end. En route, various trees get briefly highlighted in the treescape and woods acquire a lurid bright green look that is quite overpowering on sunny days.

As a rule the leafing moves from shrubs to smaller trees and on to larger trees, but there are exceptions – for example, weeping willows, hornbeams and horse chestnuts, which leaf early. These apart, the typical sequence is greening of the lower, shrubby part of the woodland (the understory) in the first week, a fuzz on smaller trees in the second week, then an explosion of greenery on most remaining trees in the third week. Within an individual species, smaller younger plants or saplings often put out leaves earlier than mature trees - presumably programmed to do so by evolution in order to catch the light reaching the woodland floor before the tree canopy closes.

There is of course variation in these timings from year to year. In 2011 and 2020 the final explosion of greenery happened as early as the second week, while in 2013 and 2015 it was not till the fourth week, and after the cold April of 2012 it did not happen until the first week of May. In 2021 leafing proceeded more or less as normal in the first half of April, but continued cold weather then put it into slow motion and the treescape was not mostly green until the second week of May. In 2018 a cold start to the month and then hot weather mid month meant everything happened in a rush in the third week.

The very first new leaves appear way back in winter. As well as evergreens such as holly and yew, some deciduous plants never entirely lose their foliage - for example privet and buddleia - or start putting out new growth as early as December or January - for example honeysuckle. The new shoots on buddleia grow to about two thirds of their final size during March and then finish the job in the first half of April, adding a bit more new foliage too. Honeysuckle foliage is usually complete by the first or second week of April. Garden privet (the familiar garden hedge plant, which has more rounded leaves) also adds new foliage in March, a process that is usually still finishing in the early part of April. Wild privet (which has narrower leaves and grows in woods and hedgerows) can be at an even earlier stage, and some saplings of it can even be entirely bare at the start of the month: more mature plants generally retain at least some leaves all winter but are not in full leaf until the second half of the month.

Bramble also for the most part also keeps a few leaves over the winter (at least in shadier spots: out in open fields it goes almost entirely bare) and as early as mid March puts out new leaf shoots from the middle of its stems. These new leaf shoots can be quite tentative in the first half of April and they often don't reach full size until the second half of the month. Being so ubiquitous, they contribute a lot to the greening of hedgerows and the understory. A much less common plant that can be mistaken for bramble is raspberry, whose stems grow upright (rather than horizontally, as with bramble) and are only slightly prickly: it grows new foliage from mid March onwards.

Other little noticed contributors to the greening of hedgerows and woodland understory include cherry plum, which leafs once its blossom is over, typically some time in late March, and elder, whose leaves have also been growing slowly since as early as January (and particularly in March) and rapidly grow to full size in the first half of April. Snowberry - a park or garden shrub, but sometimes found in the wild - starts to put out foliage from the second week in March and usually looks in full leaf in the first or second week of April, though its leaves continue to grow and do not reach their full size for another couple of weeks. Wild rose also starts to tentatively put forth leaves in March, but its foliage does not really become big until the second half of April. Dogwood leaves can remain small till the fourth week, but stand out attractively against their maroon branches. In hedgerows the climbing plant traveller's joy has tentative leaves right from the start of the month but is not fully in leaf until the third or fourth week.

Much more obvious is the leafing of hawthorn, which has a huge impact on the appearance of the countryside, covering large swathes of hedgerow and understory with a lovely green fuzz. On some smaller or younger hawthorns this can happen as early as the start of March, but the main wave can be any time from the second half of March to the first half of April (the third week of March in 2007, 2012 and 2014, the fourth week in 2011, 2017, 2019 and 2020, the first week of April in 2008, 2009 and 2010, the second week in 2016, 2018 and 2021, and the end of the second week in 2013 and 2015). The leaves remain small for a week or two, however.

On blackthorn the falling blossom (which can be any time from the first week of April to the first week of May - see April blossom and shrubs) gives way to new foliage, though there can be a short gap between the two. Some smaller blackthorns go straight to leaf without flowering at all, however, or have lower twigs leafing while the upper ones are still in flower.

Moving up in size, hazel tends to have small new leaves at the start of April, having started in mid to late March. They remain very small until the second half, however. At this early stage they look almost identical to those of hornbeam, to which they are related. Only towards the end of the month do they start to take on their final, more rounded shape, and even then they may not attain their full size until some way into May.

Hornbeam leaves are usually preceded by a mass of catkins. Typically this happens in the second half of March (not till the second half of April in 2013: in 2020 there were almost no catkins, for some reason). Leaves then start to appear about ten days later - usually the first or second week of April, making hornbeam the first source of greenery in the upper levels of woods. Once the leaves are out, the catkins last another week or so before falling to the ground. While they are still out, one is aware of just how many hornbeams there are in some parts of the south east, for example the Weald. (They are not common elsewhere in the country.) Along with the leaves, the almost invisible female flowers appear, drooping at the end of the twig, and towards the end of the month they morph into thin tassels, the beginnings of the tree's characteristic seed clusters.

Hornbeam is not the first large tree to leaf, however. That honour goes to the weeping willow, which can put out new leaves and catkins as early as the first week in March, and which shines a bright yellowy green in the landscape as a result. This effect usually lasts a little way into April before the leaf colour fades to a more normal green. (In 2018, exceptionally, weeping willow did not leaf until the second week of April and never quite attained its normal brightness.)

In late March and early April horse chestnuts follow, their brown sticky buds expanding into monstrous ovals that look like some weird fruit, and then overnight producing limp bright green leaves. Typically this process starts at the very end of March but does not get far, with the leaves mainly emerging in the first week of April (a week to ten days later in 2006, 2008, 2009, 2013, 2015, 2016 (in places), 2018, and 2021) and taking as much as two weeks to grow to full size. At the very end of April (mid April in 2011 and 2020, the third week in 2017, the second week of May in 2018 and mid May in 2013, 2016 and 2021) the spikes of candle-like flowers start to appear. Squirrels eat the flower buds and discard the leaves around them, which is why you sometimes find fresh horse chestnut leaves on the ground at this time.

At the start of April (not till the second week in 2016 and 2018, and the last ten days of the month in 2013, while in 2019 some started in the last week of March and others were delayed until the second week of April) Norway maple seems to be bursting into bright yellow-green leaves, but on closer inspection is producing flowers, with some leaflets. It remains a striking sight for a couple of weeks. Once the flowers go over, they turn into tiny winged seeds and the leaves come out, and some reject seeds may end up on the ground, though you more normally see this in May. In one cultivar of Norway maple the leaves are a bright red when they emerge.

Larch can be briefly quite noticeable in early April too. The only coniferous tree to lose its needles in winter, it has already started to put out soft tassels of new greenery in the second half of March (not to any degree until the second week of April in 2018 and in the third week of April in 2013). These are often quite small at the start of the month, but explode into a mass of bright green in the second week. Notice also the cone-like pink blooms: these are the female flowers, a floral version of the seed cones they will eventually become. These have also started in March and get gradually bigger as April goes on. The male flowers (seen on the same tree) are yellowish and small, looking like undeveloped buds.

Also at the start of April pussy willows (a collective name taking in goat willow or sallow and grey willow) are at the height of their catkin phase. There are two types of tree – male, which lose their catkins by mid month, and female, which retain green catkins to the end of April. The female trees generally put out leaf shoots fairly soon after the catkins appear, while on male trees this happens after the catkins have fallen. On both trees the leaves can remain quite small for the rest of the month. (In 2007, 2011, 2012 and 2019 the male catkins had all but finished by the end of March. In 2013 pussy willows started to bud in early March but were put in suspension by the cold weather: catkins finally came out in the second week of April and lasted till the fourth week. In 2018 catkins did not appear until the second week.)

Another willow - osier, which grows by rivers - has similar male catkins to pussy willows, though more densely packed on the branches. Once its catkins fall, it puts out dense clusters of its long thin leaves. Much more common in the south east is crack willow, which also often grows by rivers. It puts out catkins and small leaf shoots as early as the start of the month (the third week in 2013 and 2018), the male catkins yellow and sometimes looking like curly caterpillars, the female green. The male ones fall to the ground later in the month but the female ones remain on the tree. The leaves can remain small all month.

The very similar white willow has less glossy and slightly darker leaves than crack willow, with a slightly hairy underside, and its new twigs are brown while those of crack willow are yellowish (though just to confuse matters the two species do interbreed). White willow slowly puts out leaves and catkins during April, both male and female ones looking green at this stage and so being hard to tell apart, the texture of the female ones a bit more like a cluster of seeds. Towards the very end of the month the male catkins may then start to turn yellow. As in crack willow, the leaves remain quite small even at the end of April.

In mid April (right from the start of the month in 2017, 2020 and 2021, from the second week and even earlier in places in 2019, in the fourth week in 2013) the short brown catkins that have hung on birch trees all winter lengthen out, causing big problems to hayfever sufferers (birch pollen is very allergenic). The leaves generally appear at the same time, with the catkins lasting until late in the month or occasionally into May.

By this time attention has switched to the larger trees. A few sycamore - saplings and smaller trees that are not going to flower - may have started leafing in late March, but at the start of April most mature trees are still at budburst stage (with the bud showing green leaf colour). It can take a while for them to go from this to leafing proper, and some trees seem to be faster about it than others. But sometime between the second week (2014, 2017 and 2020), the third week (2012, 2016 and 2018), and the fourth week (2013, 2015 and 2021) leaves are appearing on the more established sycamores, accompanied by tassels of flowers which hang down like bunches of grapes. Some sycamore leaves look brown and tired when they unfold.

Field maple also produces flowers and leaf shoots simultaneously (the flowers initially being more prominent) from as early as the second week (not till the third week in 2018 and 2021): again, this can happen a bit earlier on saplings, which usually only produce leaves.

Poplars - both hybrid black and lombardy types - should have produced their fat red (more orangey on some species) catkins in mid to late March: if not (as in 2015, 2016 and 2018), they do this early in April. Once the catkins fall, the tree puts out leaves - brown ones in some species, yellowy-brown on hybrid black poplars - which slowly turn green.

London plane puts out new globular flowers in the second week (from the start of the month in central London), the larger female ones hanging down from the tip of the twig, and being sometimes quite red but otherwise a sort of rusty brown; the male ones small, green or yellowy-green, and a bit further back on the twig. In each case there can be more than one flower per stalk. Leaves appear at the same time as the flowers, but generally remain small until May (the tree looks a mess while they are in this state). The female flowers slowly get bigger and later in the month or in the first half of May, they turn green (actually green with brown hairs if you look closely), becoming the tree's seed balls. They then remain in this state for the rest of the summer. You also see quite a few of last year's brown seed balls still on the twigs, which may fall and break apart producing piles of silky tassels on the ground, though the timing for this is very variable.

Other trees leafing mid month (in the second week in 2019 and 2020, though not till the end of the third week in 2018 and the end of the month in 2013 and 2016) include alder, lime and rowan, the latter easy to mistake for ash due to its similar foliage. On alders and limes these leaves can remain very small till well into May. Elms are still in flower at the start of the month, and by mid month have bunches of their flat seeds. The ones you see are overhelmingly like to be wych elm, which is in fact our native species, while English elm is generally only a hedgerow shrub due to Dutch Elm Disease. The seeds are joined fairly soon by the leaves, wych elm leaves having a sharply curving point which helps to identify them. By the month's end you may see lots of the seeds on the ground, though plenty can still remain on the tree too. Note also the strange pale leaves of whitebeam, which unfold from an upright centre like tulip petals from the second or third week, and are very prominent in the landscape by virtue of their silvery tinge.

Oak can also be in flower and leaf quite widely by mid month - in 2017 and 2019 some were out as early as the first week and almost all were out in the second week - though in some years this does not happen until the third week and in 2013 it was not until the end of the month. In 2021, a particularly cold April, some were starting to leaf in the third week, but the leaves remained very tentative until the middle of May. Even in a normal year, some oaks seems to lag behind, and it is not unusual to find one only just starting at the end of the month. They produce leaves and yellow-green tassel flowers simultaneously, but the leaves are slow to grow and the flowers dominate to begin with. You have to look closely to see this, however, as from a distance the flowers look like new foliage.

Perhaps the most striking tree when it comes into leaf is beech. While some leaves may be seen from the third week (the first week in 2019), these tend to be on saplings or lower branches: the main wave of new foliage is typically not till the fourth week (as in 2010, 2015, 2017 and 2019) or even early May (2012, 2013, 2016 and 2021). When new, beech leaves hang in limp lines like washing hanging out to dry, and are one of the more breathtaking sights in the woods. Their appearance often coincides with the fullest phase of the bluebell season, the bright green leaves providing a brilliant backdrop to the purple-blue of the flowers.

By this point most of the bare trees you see are ash. It puts out its strange flowers - looking like frizzy lettuce - as early as the start of the month, though this is very variable (in the last ten days of March in 2017, in the first week of April in 2020, in the second week in 2015, 2016 and 2018, variously from the first to the third week in 2021, and in the last week in 2013: in 2014 and 2019 there were no flowers at all). There are in fact two types of flower - the more compact male ones and the female ones which are already flecked with the seeds to come. Within a week or two the male flowers fall to the ground while the female ones lengthen into feathery fans and slowly become more seed-like. From a distance these seed fans can make the tree look as if it is leafing, but it does not actually do so until the very end of April, the first week of May, or - in 2012, 2014, 2016, 2019 and 2021 - the second week. Even in normal years its foliage can remain tentative until late in May. (In 2020, very remarkably, all ashes put out leaves from mid April onwards, though they were still only about half size by the month's end.)

One other laggard is sweet chestnut, which mostly does not leaf till May, though in the second half of April you may see some small leaves, usually on saplings or trees that have been coppiced in the not too distant past.

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