Ivy

Ivy (Hedera helix s.l.) - A plant that does the job of ten others.

Why we might grow ivy instead!

I know. Ivy isn’t that sexy.

It doesn’t have flamboyant flowers. It doesn’t scream for attention. It just gets on with it. But if we’re serious about asking what a plant actually does ecologically, ivy deserves a closer look.

When I talk about ivy here, I’m talking about Hedera helix sensu lato - ivy in the broad sense - which includes the two native plants, common ivy (Hedera helix) and Atlantic ivy (Hedera hibernica). Because in the field, and subsequent recording, they’re difficult to tell apart conclusively without microscopic examination - the leaf hairs are different. They do have some traits that can get us some way there though: Atlantic (also called Irish) ivy can have 5 to 7 lobed, broader and shorter leaves where common ivy usually has 3 to 5. In its native range Atlantic ivy is a plant of western Britain, also it is more vigorous, less dark and has less tendency to climb - its leaf hairs, by the way, lay flat where common ivy’s stand up. Ecologically speaking though, they behave in much the same way.

Ivy supports 206 recorded insect interactions.

That’s made up of:

• 106 phytophagous (larval / plant-eating) insects

• 100 pollinators

For metamorphosing insects ivy feeds at two crucial stages of their lives.

As larvae, insects consume the tissues of the plant, the plant itself - its leaves, stems, roots, buds and even flowers. And those larval insects include: 

3 butterfly species’ caterpillars, including the holly blue - of which it is the primary food plant along with holly (Ilex aquifolium). Holly feeds mainly the spring brood and ivy the summer.. 

60 macro-moth caterpillars with names as extraordinary as their markings and habits such as: Merveille du Jour, Green-brindled Crescent and Bloxworth Snout. 

Alongside them are 43 other plant-eating insects - leaf-mining flies, caterpillar-like sawflies, micro-moths caterpillars, and beetle grubs, that mine, bore, gall, graze and suck, often living within the plant as well as feeding on it. 

Plant-eating isn’t exclusive to larvae, though. Many insects that undergo incomplete metamorphosis, such as true bugs, hatching as smaller, wingless versions of the adult and gradually moulting into maturity, feed on plant sap throughout their lives. Certain beetles chew leaves, seeds or flowers in both stages.

Others, as adults, use its flowers as a nectar and pollen resource. What we call pollinators.

And ivy’s late flowers - opening from September through to November, support:

100 pollinating species:

18 bees, including solitary bees such as the ivy bee Colletes hederae that, as adult and larvae, feed almost exclusively on ivy pollen and 12 plus bumblebees. 

30 hoverflies, 9 micro-moths, 4 butterflies, and 39 other insect groups

That ivy flowers late, means it's in bloom when almost nothing else is

Then there is structure.

Ivy is heteroblastic - it has two life stages. The juvenile phase climbs and reaches, clinging by aerial roots. And when we say roots in this sense, we're not talking about roots that go into the ground to sustain the plant. We're talking about adventitious roots that just cling on, literally glueing themselves to the surface of a tree or wall. Ivy, like most plants, gets its water and nutrients from roots in the ground.

In the adult stage, usually after 5 to 10 years, it becomes much more like a normal shrub not having the aerial roots, so not clinging on anymore. Forming more oval leaves, flowering and fruiting. So is in its reproductive stage. 

Actually not dissimilar to the metamorphosis of a butterfly or moth or other insect. Where we have the caterpillar stage which is just feeding, feeding, feeding, with no sexual reproductive organs, and then we have the adult stage where it reproduces. 

So if we cut ivy back before it matures, we remove the very pollen, nectar and berries that are so much of the value to wildlife that ivy offers..

The problem probably comes with ivy if it finds a crack, for instance in a building it will send shoots into that crack or the same in a tree and the growth in its adult stage can be pretty heavy and quite a lot of it. So if you get a storm it will possibly topple the tree over.

Where it’s found a good position and is doing no structural harm it really then comes into its own, forming the dense evergreen growth that creates overwintering shelter for brimstone and comma butterflies, lacewings, spiders and countless others. 

Its berries ripen in late winter, providing high-fat, high energy food for blackbirds, thrushes and starlings. Its tangled framework offers nesting cover and bat roosting habitat. It forms ground cover, vertical habitat, shrub layer and woodland edge and tree form all in one plant.

It is, quite simply, ecological infrastructure that would require maybe ten other plants to equal.

And yet when we choose climbing plants, we often reach for appearance first.

Virginia creeper.
Boston ivy.
Climbing hydrangea.

Virginia creeper — Parthenocissus quinquefolia
Native to North America. Introduced 1629.
Supports 2 phytophagous insects and no recorded pollinators. It is listed under Schedule 9 of the Wildlife & Countryside Act, meaning it is ‘illegal to plant or cause this species to grow in the wild’ yet we can buy or specify it to plant in any private or public space. Simply madness.

Boston ivy — Parthenocissus tricuspidata
Native to China and Japan. Introduced 1862.
Supports 1 phytophagous insect.

Climbing hydrangea — Hydrangea petiolaris
Native to East Asia. Introduced 1835.
No recorded insect interactions.

They are chosen mainly for autumn colour and ornamental effect. But functionally, they are almost silent.

These plants aren’t bad, in and of themselves, in fact, they I’m sure, are fantastic where they are native and contributing to their own complex set of insects and other creatures. They just don’t really pay their way, ecologically speaking, when removed and transplanted into an entirely different environment. 

What’s more, plants like Virginia creeper can actually be putting more pressure on an already stressed ecosystem.

Pretty, perhaps, but in my opinion, not beautiful.

I feel a caveat is necessary. The data referenced here has been collated from respected sources, but it is not infallible. There will undoubtedly be unrecorded interactions. So, it is best understood as a barometer, helping us steer an ecological course, rather than the final word.

Even so, the pattern is clear.

If our aim is to create landscapes that genuinely work for nature - feeding insects at multiple life stages, offering shelter through winter, linking birds and bats into the system - then ivy is not something to casually replace. But to keep it, buy it and specify it for projects, you’d have to look hard to find a good reason why you wouldn’t use it.

Keep it off roofs for sure. But let it mature. Let it flower. Let it fruit.

You can watch the accompanying film here:
https://youtu.be/PMkF3CGjXx4

Andy.