Ilex aquifolium | holly

Understanding the wildlife value of this winter stalwart

Holly tree, ilex aquifolium, with its signature red berries and non-spiky leaves emerging out of the reach of deer (photo by Christopher Lyon Anderson)

Somewhat unfairly, I’ve had a love hate relationship with holly over the years. I’ve always loved seeing the red berries and their association with this time of year as we approach the winter solstice on the 21 December. And I love the shape of each individual leaf. But I’ve never really liked the look of the overall tree, with its dark shiny, curled and spiky leaves.

The shape of the stems and branches, the way they fire out all over the place, can look rangy and odd, while those spiky leaves are a literal pain in the bum, or more often, hands. Those shiny-muted green leaves remind me of dull, smelly, uncomfortable Barbour jackets and Landrovers, a feeling I associate with cold mud and an out-of-touch elite of people who hunt foxes and pheasants for fun (don’t worry if you own a Barbour jacket or Landrover, I’m not tarring everyone with that brush!)

But recently, I’ve decided to reclaim the humble holly in my mind, to look at it fresh. Because on our farm we have a few holly trees that are pretty much the only evergreen plant around us, the rest of the valley and our garden is almost exclusively deciduous. Sensible of them really, to avoid the worst of the winter, which can be very harsh here. Standing strong in the face of the worst weather, those holly trees look beautiful, and I realise it’s because they are trees, not maintained as hedges or shrubs. Allowed to grow into their full natural shape, those hollies have a stature to them I can admire. Then, there is the wildlife value I’ll come onto below.

Need to know information about Ilex aquifolium

Allowed to grow into its natural shape, a common Holly in the UK will grow into a medium sized tree, somewhere between 8 - 10m tall, and about a third less than that wide. It is evergreen, holding onto its leaves year round. Like all evergreens, it does still drop older leaves throughout the year, creating a long lasting groundcover of dead leaves.

Ilex aquifolium is the botanical name of the common holly we know in the UK. This species originates from the western side of Europe, Scandinavia, down to Spain and Northern Africa. There are just under 600 different species of holly around the world, this is only one of them. The specific epithet ‘aquifolium’ means quil-like (aqui) and leaf (folium), so, spiky leaf.

It is now understood, thanks to recent research, that Ilex aquifolium can switch its defensive spikiness on and off depending on responses to attack. This is why you will usually see spiky leaves on the trees lower down, and smoother rounded leaves higher up. It was previously thought this was to do with age, but the trees are able to adjust their chemistry to react in real time. So, in an area where they are being eaten a lot by deer, they will make the lower leaves spikier. And deer do love to eat holly in winter, even when it’s spiky, it’s an important food source for them. This is why your clipped holly hedges remain painfully spiky! They think you are a hungry herbivore.

Holly is dioecious, which means each plant is a specific sex, either male or female. Dio meaning two, so you need two trees. If you want red berries, you need to make sure you have a female tree because male trees only produce the nondescript small white flowers in summer. It is common in nature for many dioecious plants to change sex later in life.

One interesting factoid for you, if you walk around in woods, you’ll often notice holly saplings growing directly out of the roots of other larger trees. This is usually called a mother tree, because it’s protecting the other tree growing beneath it. I don’t know whether this phenomenon, which is particularly true of holly, is because birds or mammals are dropping the seeds beneath the other tree, or because holly is adept at growing in those conditions. Take a look in a woods near you, once you see holly saplings growing from under larger oaks, beech and birch, you’ll see them everywhere! Personally, I think it’s some kind of woodland magic.

How is holly used by wildlife?

One of the reasons I like holly more these days is its vital role for wildlife. The berries ripen later than others in early winter, making them an important food source for birds and small mammals.

The dense spiky nature of its leaves make it excellent shelter for birds of all sizes, to roost and nest within.

Because it is evergreen, it provides important shelter for animals to hide within when it rains or is very windy. I’ve often thought on our farm, that if I had to snuggle deep inside a holly during the worst weather, I’d be so grateful to them.

Many insects rely on holly, the beautiful holly blue butterfly being the most obvious, Celastrina argiolus. Also many moths, including the double striped pug, Gymnoscelis rufifasciata, and yellow-barred brindle, Acasis viretata. Beetles and other insects feed on the leaves.

Sealing the deal for me are the hedgehogs, that like to take shelter in the dry leaf litter, they’re used to spikes after all. Holly acting as a natural umbrella, drier, cosier and safer than many other spots. Which will be true for other small mammals, including mice, weasels, stoats, badgers, foxes and more.

All in all, a holly tree is a good addition to a garden.

Is holly edible?

No, it’s toxic to humans.

How to propagate holly

Holly can be grown from seed by smushing up some berries into the top of a pot of compost in early winter. Leave it outside and in spring, the seeds should germinate.

Alternatively, take hardwood cuttings of young branches about a pencil thick and 20cm long in autumn or winter. Remove the lower two thirds of leaves and stick that bottom end into the soil somewhere or in pots of peat free compost. Leave and they should root.

Cutting are the best way to ensure you have a female berry producing plant, as you can take them from a tree you know produces berries.

Using holly in design

Holly leaves and berries in a natural homemade festive wreath

Personally, I would plonk a holly somewhere it can grow into a tree. They grow happily in full shade or sun, and in any soil as long as it’s not bone dry. Use it as the back bone of a garden with other things in front for most of the year, letting it take centre stage in winter when its berries can be seen. You could use it for shelter to protect other plants from wind.

I would suggest trying to make sure your holly is a female for the berries - you can only tell by seeing it with berries growing on it.

There are lots of cultivars and other species of holly you can investigate, though I find them all much of a muchness and simply like the wild tree.

I wouldn’t personally recommend holly for hedging as it’s so spiky, but like us, certainly include some in a mixed hedge for the wildlife benefits discussed above. Though one of the benefits, as reader Paul Fletcher reminded me, is that because it is a tree, it is one of the plants that can make a high hedge of 3-4m and still be green from top to bottom.

And of course, it’s useful for making festive decorations - personally I don’t celebrate Christmas as I’m not religious but I do like to celebrate the end of the year and all things festive! Homegrown decorations certainly beat anything bought in shops, to me anyway.

p.s. I’m now on the free social media app BlueSky here