Jeremy Bartlett's LET IT GROW blog

With Christmas approaching, I’ve decided to write about Holly, Ilex aquifolium.

In 2017 I wrote about Ivy, Hedera helix, Holly’s companion in the traditional carol “The Holly and the Ivy” and in 2015 I wrote about Mistletoe, Viscum album, that other favourite festive evergreen. But today it’s Holly’s turn at long last.

Holly, Ilex aquifolium, is a familiar native evergreen tree or shrub. It can exceed ten metres tall (30 feet) – The Trees and Shrubs Online website says “up to 80 ft high” – but more typically it reaches two or three metres (seven to ten feet) in height and spread. Its berries and glossy leaves, often adorned with spiny teeth, make it an attractive midwinter plant and it is often cut used as a Christmas decoration.

Holly in the British Isles

Holly is found almost throughout the British Isles, with a distribution spot in most ten kilometre squares in the BSBI Online Plant Atlas. The exceptions are some islands and upland areas, although Ilex aquifolium is able to grow at an altitude of 600 metres above sea level in the Lake District.

Holly In Gardens

Holly makes an adaptable garden plant. It is tolerant of industrial pollution and can be used for topiary, clipped into formal shapes, as at the National Trust’s Tyntesfield in Somerset. It makes a good hedge, either on its own or mixed with other species that cope with a regular trim, such as Beech (Fagus sylvatica) or a mixture of other wild species.

The Plant Atlas notes that widespread planting has completely obscured the native distribution of Ilex aquifolium and my nearest Holly has been planted in gardens and in the local cemetery.

Holly in Hedges

In the wider countryside, Holly grows in hedges and as isolated roadside trees, usually as the remnants of a hedge.

Why do Holly trees survive when the rest of the hedge has been removed?

In “Flora Britannica” Richard Mabey (note 1) mentions the widespread belief that cutting down a Holly tree will bring bad luck. This may have “a time-lag of as much as forty years” so is difficult to prove. On a more practical level perhaps the tree is considered useful. The outline of a Holly tree could be used as a useful landmark to fix on when ploughing a field in winter.

While it may be unlucky to remove a whole Holly tree, there is a long tradition of bringing cut branches indoors at Christmas and, before that, to celebrate the winter solstice. Holly branches also make nutritious and palatable forage for livestock and have often been cut for that purpose.

Thomas Hale was a fan of Holly hedges: “No hedge is so beautiful; none so strong. When well grown, it appears as a wall rather than a hedge, and is altogether impenetrable by cattle.” (note 2).

Holly at Staverton Thicks

One of my favourite places to see Holly is Staverton Park in Suffolk. A footpath from the main road winds through dark woodland (Staverton Thicks) where large Holly trees grow, sometimes sprouting upwards from fallen trunks.

At Staverton the Holly trees surround ancient oak trees and some have taken root high up in the oaks’ branches. Others over-top them and in “The History of the Countryside” Oliver Rackham describes how “over-shadowed giants moulder in the twilit shade or lean half-fallen against other giants” (note 3).

Further into the Park the path heads out of the Holly trees and on a sunny day the visitor emerges, blinking, to see an expanse of magnificent oaks growing out in the open amongst Bracken (Pteridium aquilinum) (note 4).

Holly Outside the British Isles

Ilex aquifolium is a member of the family Aquifoliaceae. The family contains just one genus, Ilex, of which there are over 570 species worldwide. The specific name aquifolium means “with pointed leaves”.

Outside the British Isles, Ilex aquifolium is native in other European countries (but extinct in Sweden) and in Morocco, Algeria and Tunisia. It typically grows in the shade of oak and Beech trees. Holly often grows in moist places but it can cope with summer drought as well as winter frosts. (The Royal Horticultural Society gives it a hardiness rating of H6, “hardy in all of UK and northern Europe (-20 to -15 Celsius)”.) Holly doesn’t like prolonged frosts or waterlogged soils.

Holly has been introduced into Turkey, Lebanon and Syria, parts of Canada and the United States and New Zealand and parts of Australia. In North America Holly can be very invasive, quickly spreading into native forests and crowding out native species.

Holly seems to be increasing in abundance at the eastern edge of its European range, as well as in eastern England.

Leaves and Berries

Holly is quite slow-growing in the British Isles and has a high tolerance for shade. Each leaf can stay on the plant for three to four years, saving the plant energy.

In a natural setting, where Holly’s lower leaves are prickly to deter browsing herbivores but leaves higher up the plant have fewer prickles. In addition, Holly can adapt to browsing by growing pricklier leaves.

Ilex aquifolium is a dioecious plant, with separate male and female trees. Female trees start to produce berries from about twenty years old. Each scarlet berry contains four seeds and some years are better for berry production than others. Traditionally a year with prolific Holly berries is said to warn of a harsh winter but more likely reason is that the spring lacked a late frost and there was plenty of sunshine in July.

Some garden varieties of Ilex aquifolium are self-fertile (such as ‘J.C. van Tol’) and if you want berries from just the one tree, these are the best option. Beware that some cultivar names are rather confusing and Ilex aquifolium ‘Golden Queen’ is a male variety, while Ilex x altaclerensis ‘Golden King’ is female.

There are varieties of Holly with different shaped leaves and more or less prickles, either all green or variegated. The Gardeners’ World article “10 holly trees to grow” gives some examples. If you prefer yellow berries to the normal scarlet ones, varieties such as Ilex aquifolium ‘Bacciflava’ are available.

Birds such as Blackbirds and Mistle Thrushes enjoy Holly berries but the berries are mildly toxic to humans. Symptoms of poisoning include diarrhoea, vomiting and stupor, but only when consuming large quantities. The Plants for a Future site mentions using the leaves of Ilex aquifolium as a tea substitute and the related Ilex paraguariensis is used to make yerba-maté (note 5).

Holly and Wildlife

As well as eating the berries, birds appreciate the dense shelter that Holly provides and insects can use Holly’s protection too.

Only a small number of insects eat Holly leaves but the mines of the Holly Leaf-miner, Phytomyza ilicis (an Agromyzid fly) are found on practically all Holly trees, in my experience.

The Holly Tortrix moth, Rhopobota naevana, also feeds on Holly.

Holly flowers – remember, they are normally male and female on separate trees – are white and come in small bunches (note 6). They are produced from May to August and the flower buds, berries and terminal leaves are used as a foodplant by caterpillars of the spring brood of the Holly Blue butterfly, Celastrina argiolus. The summer brood of the butterfly uses Ivy, Hedera helix.

Both foodplants occur in churchyards and cemeteries, as well as in larger, established gardens, all of which are good places to look for the butterfly.

Numbers of Holly Blues fluctuate from year to year. Holly Blue numbers are controlled by the butterfly’s parasite, the solitary wasp Listrodromus nycthemerus. 

Holly and Fungi

In mid-winter dead, fallen Holly leaves usually have a dark speckling on their upper surface, caused by Holly Speckle, Trochila ilicina. This fungus feeds on dead leaves rather than living Holly trees.

In 1989 Holly Leaf Blight, Phytophthora ilicis (note 7), was accidentally introduced into the British Isles from North America. It causes Holly leaves to blacken and drop. It is very disfiguring  but can be controlled, at least to some extent, by improving air flow around the plant and removal of diseased leaves and branches. I’ve seen it a few times in Norfolk in shady churchyards or damp woods but so far most Hollies seem unaffected.

The Holly Parachute, Marasmius hudsonii, is a scarce, near mythical tiny mushroom that grows on dead, moist Holly leaves. I have never seen it but the First Nature website has some lovely photographs. There are currently just two records of the fungus in Norfolk, at Swanton Novers in October 2003 and at Wheatfen in September 2005.

Holly Timber

Holly timber has a tendency to warp, so must be dried slowly and carefully. The wood is white and it is strong, resistant to impact and can be given a fine surface. It can be used as a veneer and is prized as an inlay by cabinet makers. It has been used for handles of tools and riding whips.

Holly also makes a good firewood because it has a high oil content and will burn when green as well as when seasoned (note 8).

Holly Place Names

“Flora Britannica” gives examples of several places in the British Isles named after Holly.

These include Hollington in Derbyshire, Hollingworth in Cheshire and, nearer to home, Hulver in Suffolk. (“Hulver” is the Middle English name for Holly.) Less obvious perhaps is Cullen on the Moray coast, said to be derived from the Gaelic  word for Holly (note 1).

In his book “The New Forest”, Colin Tubbs mentions that the cultivation of Holly as a fodder crop was widespread in England and Wales from the 13th to 18th centuries and probably before that too. Stands of Holly in the New Forest were known as “holms” and “hats” and these words survive in names such as Standing Hat and Holm Hill. In the Pennines, Cumbria and Welsh Marches Holly has resulted in a number of “hollin” place names (note 9). Richard Mabey gives examples such as Hollinroyd (Holly clearing), Hollin Hall and Hollingreave Farm, as well as Hollington in Derbyshire and Hollingworth in Cheshire (note 1).

New Forest ponies love the nutritious, evergreen Holly, which forms an important part of their winter diet (note 9). They are able to bite off and chew whole stems of prickly gorse and Holly.

As you can see, Holly, like Ivy, isn’t just for Christmas.

Notes

Note 1 – Richard Mabey, pp 244 – 251, “Flora Britannica”. Sinclair-Stevenson, 1996.

“Scottish Hill and Mountain Names” by Peter Drummond (Scottish Mountaineering Trust, 1992) gives “cuilionn” as the Gaelic word for Holly.

Note 2 – Quoted in John Wright, “A Natural History of the Hedgerow”. Profile Books, 2017.

Note 3 – Oliver Rackham, page 145, “The History of the Countryside”. J. M. Dent & Sons Ltd, London, 1986.

Note 4 – One of these trees held the Magpies’ treasure in the third series of “Detectorists“.

Note 5 – I tried yerba-maté a few years ago and I found it far too bitter and won’t bother to repeat the experience. I much prefer “proper” tea made with Camellia sinensis.

Note 6 – See the Wildflower Finder website for some lovely pictures of Holly, including its flowers.

Note 7 – Phytophthora ilicis is a type of oomycete. Oomycetes are filamentous eukaryotic organisms and are now considered to be Stramenopiles rather than fungi.

Note 8 – From pages 275 – 277 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 – Colin R. Tubbs, “The New Forest”. New Naturalist series, Collins, 1986.

Page 126: Studies of the diet of New Forest ponies showed a definite seasonal pattern, with grass forming most of their diet in May, June and July. Between September and May gorse, tree leaves and twigs (notably Holly), moss and heather were more important, along with Bracken fronds in August and September.