Jeremy Bartlett's LET IT GROW blog

February is catkin season and Hazel catkins – known as lamb’s-tails – are one of the delights of late winter and early spring.

Hazel (a.k.a. Common Hazel), Corylus avellana, truly is a beautiful, adaptable, useful and edible plant.

Beautiful

Hazel is wind pollinated and the catkins are Hazel’s male flowers. Bearing masses of pollen, they shake in the slightest air movement, sending clouds of pollen into the air. They shine out from an otherwise dull background on a sunny day, in woods, hedges, parks or gardens.

The female flowers are on the same plant (Hazel is monoecious) but you need to look a bit closer to see them.  They are very pretty and resemble tiny bright red sea anemones. (Rarely, they can be white – see postscript.) They’re best observed with a hand lens, measuring just 4 mm (0.16 inches) across.

There are around 14 – 18 species of Corylus worldwide (note 1).

Adaptable

Our native species of Hazel is Corylus avellana (sometimes called Common Hazel) and we are fortunate that it is very widespread in the British Isles, occurring in nearly all ten kilometre squares.

Further afield, Corylus avellana is a native of most of Europe. It has also been introduced to Crete, the Azores, Newfoundland and Oregon.

Corylus avellana was one of the first woody plants to recolonise Britain after the last Ice Age, arriving soon after Birch trees (Betula sp.). Birch and Hazel are both in the Betulaceae (Birch family), along with Hornbeams and Alders (note 2).

Hazel is a very adaptable plant. It will grow in damp or dry soils, whether they are slightly acidic, neutral or calcareous, but it is happiest in moist, base-rich conditions. It forms the understorey in many woods  and will also grow along riverbanks, on cliffs and in gullies, including the grykes of limestone pavements. In the west of Scotland it can form entire woods, such as at Ballachuan Hazelwood on the island of Seil. Hazel does best in sunlight, though it is capable of surviving in a leggy and slow-growing form in dense shade.

Hazel leaves are oval with a double toothed, serrated edge, ending in a point. They are hairy, especially on the undersides, and when young they have a beautifully soft texture. They turn yellow in autumn and the display of colour is usually best in early to mid November here in Norfolk.

The Woodland trust document how a Hazel changes throughout the year in a lovely video, “A year in the life of a Hazel tree“.

Useful

Hazel occasionally grows as a single trunked tree but more usually as a suckering shrub, with multiple stems. If a stem damaged or is cut down the Hazel will produce more upright stems from the base. This makes Hazel a very useful plant.

Hazel was often coppiced to provide poles, stakes and other useful materials. Coppicing involves repeatedly cutting down young tree stems every few years, traditionally with a billhook. A chainsaw is usually the preferred tool these days, but a bowsaw works well and is a safer tool in inexperienced hands. (It’s what I use.)

Hazel can be used to make hurdles, fencing, divining rods, pea and bean supports and walking sticks.  Hazel also makes excellent charcoal, formerly for making gunpowder and nowadays for the use of artists. Hazel firewood is excellent: it burns well and is easy to cut and stack.

Wattle and daub buildings are made from a framework of wooden strips (wattle) covered with a sticky material (daub), typically made from clay, animal dung and straw. In the British Isles, split Hazel poles were typically used to make the wattle (note 3). Hazel could also be used to make spars for thatching roofs.

Hazel is tough and pliable and it can be split lengthways, twisted and bent at sharp angles without breaking. Strips of Hazel can even be tied in knots to bind up bundles of cut Hazel poles (known as faggots). Nowadays these bundles are used to strengthen riverbanks and wattle screens have been used as sound screens, to deaden noise from main roads.

The frequency of cutting determines the size of the coppice products that are produced. As Hazel responds by producing more and more stems, each coppice stool becomes bigger. Coppiced trees remain in a juvenile state and can live for many centuries, while a Hazel that isn’t cut usually lives for 80 to 90 years (note 4). By rotating coppice compartments in a wood (i.e. not cutting everything at once) it was possible to have a continuous supply of woodland products.

By the mid twentieth century coppicing had stopped in many British woodlands. This caused a serious decline in species of wildlife that had benefitted from open areas in woodland, such as the Pearl-bordered Fritillary (Boloria euphrosyne). and Small Pearl-bordered Fritillary (Boloria selene).

With its dense growth, coppiced hazel also provides shelter for ground-nesting birds, such as Nightingales, Nightjars, Yellowhammers and Willow Warblers.

Nowadays coppicing is used as an important part of the management of nature reserves and it is sometimes possible to raise funds at the same time by selling poles, pea sticks and firewood.

Hazels in hedgerows are sometimes used to make walking sticks and young shoots can be pegged down to provide the curve in the walking stick handle (note 5).

Hazel is a good hedging plant and its attractiveness and many uses mean that it has been and continues to be planted. Hazel makes a good garden plant and we have a couple of small specimens in our back garden. It is very hardy, down to -15 to -20 degrees Celsius (hardiness H6). Hazel needs a winter chilling period of 800 – 1200 hours below 7 degrees Celsius (45 Fahrenheit) so won’t grow well in tropical or sub tropical climates.

Hazel can sometimes reach 15 metres (49 feet) in height, with 3 – 8 metres (10 – 26 feet) tall being more typical. But regular coppicing or pollarding (cutting higher up, to promote a dense head of foliage and branches) will keep it in check, as well as providing useful poles, sticks or firewood.

I have to admit a dislike of Corkscrew Hazel, Corylus avellana ‘Contorta’, which is often grown in gardens. The twisted stems look fine in winter but the leaves are slightly contorted too and make the plant look sickly or diseased. There is also a form with red leaves and catkins, Corylus ‘Red Majestic’.

Edible

Whether a Hazel grows straight or twisted, delicious hazelnuts form from the pollinated female flowers.

The nuts can be eaten as early as August, before they are fully developed, or when ripe in September. They will store well (in a mouse proof container). They are rich in protein and contain significant amounts of vitamin E, thiamine, and magnesium, though Hazel nuts (and pollen) cause allergic reactions in some people (note 4).

Hazelnuts were a staple food for prehistoric peoples and in Celtic legend they were an emblem of concentrated wisdom: sweet, compact and sustaining.

There’s also an association with mild anarchy, which I like. In the nineteenth century were appreciated by “idle and disorderly Men and Women of bad Character” from Bishop’s Stortford in Hertfordshire, who visited Hatfield Forest in large parties “to gather the Nuts or under pretence of gathering Nuts to loiter about in Crowds… and in the Evening… Drink in the Forest which affords them an opportunity for all sorts of Debauchery” (note 5).

“Nutcracker Night” in November was when stored hazelnuts were first opened. In some parishes there was a custom of bringing nuts into church on the following Sunday to be cracked noisily during the sermon (note 5).

Hazel Dormice and Squirrels are very partial to the nuts, as are Nuthatches and Great Spotted Woodpeckers.

The female Nut Weevil, Curculio nucum, lays her eggs in the developing nuts (one per nut). The larva feeds inside the nut, resulting in a hollowed out nut. Once the nut falls from the tree in late summer the larva makes a hole in the nut, emerges and builds a cell in the soil beneath the Hazel bush. The larva spends one or more winter in the soil before pupating in late summer or autumn and then emerging in the following spring.  Commercial orchards tend to spray insecticides to control the weevil but the main growers of Hazelnuts (Turkey, Italy, France and Spain) are looking at other methods of control, such as nematodes or the fungus Beauveria bassiana, to kill the larvae in the soil.

I planted a Kentish Cobnut (Corylus maxima, see below) on the allotment twenty years ago and in the first few years we had good crops of nuts. In the last ten years more than half the nuts have been eaten by Nut Weevil larvae. I don’t mind sharing – up to a point – but I think the Nut Weevils now have the upper hand. I don’t want to spray; so nowadays the tree is mainly a source of pea sticks and firewood, as well as providing cheer from its catkins in spring and welcome shade in summer.

Deer are partial to young Hazel shoots, meaning that young regrowth from coppicing may need to be protected by a fence or from pieces of cut brash laid on top of the coppice stools.

106 species of insects and mites are associated with Hazel (note 6). One of my favourites is the Hazel Leaf-roller, Apoderus coryli, a beetle with red elytra and a black head which narrows at the rear forming a distinct neck. The adult female cuts and rolls up Hazel leaves to provide a safe place for her larvae to develop (note 7).

Fungi such as Spring Hazelcup (which I wrote about a year ago) and Hazel Woodwart live on dead Hazel branches and the Fiery Milkcap forms a mycorrhizal relationship with living Hazel.

Less happily, pathogenic bacteria Pseudomonas avellana and P. syringae pv. coryli cause bacterial canker in Hazel. In Spain and Poland Hazel is sometimes affected by Apple Mosaic Virus. A mould on the nuts (nut grey necrosis) is caused by the fungus Fusarium lateritium (note 4).

Some Other Hazels

Filbert / Kentish Cob

My Kentish Cobnut is actually a relative of Hazel, Corylus maxima, known as the Filbert. The name ‘Filbert’ comes from St. Philibert’s Day, 20th August, which is when the nuts are supposed to be ripe (note 5).

Like Hazel, the Filbert forms a multi-stemmed shrub. The nuts of Corylus maxima are larger and longer than those of Corylus avellana. The bracts, which surround the nut, extend beyond the end of the nut, whereas those of Corylus avellana don’t.

In the early twentieth century there were some three thousand hectares (just over 7400 acres) of Cobnut plantings in Kent but barely 100 hectares remain, many of which are derelict (note 8).

Hybrids occur between the two species but their distribution is confused by planted larger-fruited varieties of Corylus avellana (note 9).

Turkish Hazel

If you see a Hazel with a single trunk with flaky grey-brown bark, it is likely to be a Turkish Hazel, Cornus colurna. It is a native of the Balkans, northern Turkey, northern Iran and the western Himalayas. The first trees were probably introduced to the British Isles by John Rea around 1665 (note 10). It doesn’t produce sideshoots like Corylus avellana and Corylus maxima.

Turkish Hazel makes a good street tree because of its growth habit – a single trunk and narrow crown – and tolerance of air pollution, drought and having its roots covered in paving or tarmac. it is just as hardy as Corylus avellana. It can provide a rootstock for Corylus avellana, creating a Hazel that won’t sucker.

There are lots of Turkish Hazel trees in Norwich, planted as street trees and in parks. In Earlham Cemetery they have been planted as single specimens and form an avenue east of South Lodge, to replace a previous avenue of Elms that died from Dutch Elm Disease in the 1970s and 1980s.

The nuts are edible but smaller and tougher-shelled than those of Corylus avellana. They grow in clusters and each nut is surrounded by curly laciniate bracts. In Earlham Cemetery the Grey Squirrels love them.

Notes

If you’d like to read more about Hazel, I recommend John Grace’s blog post, Plant of the Week, 6th March 2023 – Hazel – Corylus avellana.

Note 1 – There is some debate over the number of species of Corylus in eastern Asia.

Note 2 – The Betulaceae also contains Hop-Hornbeams (Ostrya, native to southern Europe, southwest and eastern Asia, and North and Central America.) and Hazel-Hornbeams (Ostryopsis, from China). The former are sometimes planted as ornamental trees in the British Isles.

Britain has three native species of Birch: Silver Birch (Betula pendula), Downy Birch (Betula pubescens) and Dwarf Birch (Betula nana). Downy Birch favours wetter and more peaty soils and Dwarf Birch is confined to moors and bogs in the north.

Note 3 – The wattle and daub building technique dates back at least 6,000 years. The materials used vary according to what is available locally. In Australia, for example, early European settles used Acacia rather than Hazel.

Note 4 – Enescu C.M., Durrant T.H., de Rigo, D., Caudullo, G., “Corylus avellana in Europe: distribution, habitat, usage and threats” in “European Atlas of Forest Tree Species” (Publication Office of the European Union, Luxembourg, 2016). Available to download as a PDF.

Note 5 – From pages 88 – 91 of Richard Mabey’s “Flora Britannica” (Sinclair-Stevenson, 1996). Well worth a read, it is packed with information about Hazel, its uses and folklore.

Note 6 – From page 53 of “The Tree Book” by  J. Edward Milner (Collins & Brown, London, 1992).

Note 7 – Most British records of Apoderus coryli are from England and Wales. A similar species – Oak Leaf-roller, Attelabus nitens – does the same with Oak leaves.

Note 8 – From pages 230 – 235 of “The New Sylva: A Discourse of Forest and Orchard Trees for the Twenty-First Century”  by Gabriel Hemery and Sarah Simblet (Bloomsbury, London, 2021).

Note 9 – Pages 318 – 319 of “New Flora of the British Isles“ by Clive Stace (Fourth Edition, 2019).

Note 10 – From pages 220 – 222 of “Alan Mitchell’s Trees of Britain” by Alan Mitchell (Harper Collins, 1996).

Postscript, 27th February 2023 – White Flowers

Many thanks to Iris Millar, who has just sent me photos of white female flowers on a couple of Hazel trees in Carnfunnock Country Park near Larne, County Antrim.

One tree had completely white flowers and a second one had white flowers with a hint of pink at the end. She tells me: “One of the trees had been planted by a local school in 2012. The other tree was probably the same vintage. There was quite a line of planted trees, all of which had been chopped to a height of around 5 feet, as well as many original hazels throughout the park. Of all the trees I looked at, only two of the planted ones had some white flowers.”

I will keep a look out for more examples.