NOMENCLATURE
All ivies are of the genus Hedera but there are several species, of which Hedera helix is the most common. Within the species there are hundreds of different ivies - whether you call them varieties, cultivars or clones does not matter between friends. In fact the huge choice can be somewhat confusing, which leads to three problems with ivies:
The differences between some of them are only really apparent to the fanatical enthusiast and in some cases the same ivy goes under more than one name.
Many of them have a nasty habit (or wonderful habit if you are an enthusiast) of mutating or reverting.
Even without mutation, the young and old leaves of a clone may look different, they may differ according to the time of the year and will vary according to habitat and treatment.
This inevitably leads to confusion and there is plenty of opportunity for mis-labelling. Also, descriptions in catalogues are not always consistent.
The list given below is a representative selection of the various forms which I have found to be sensibly stable.
BOTANY
All ivies are evergreen but it is also worth noting that they have the odd characteristic of having both juvenile and adult leaf forms. The juvenile form is usually, but not always, lobed. For reasons not entirely understood, when the plant reaches a certain height or age or something, the leaves lose their lobing and take on a more narrow elliptical shape. This process is called dimorphism and marks the point at which flowers and then berries are produced. If cuttings are taken from the adult or arboreal growth they will retain this form and can develop into free standing shrubs.
The berries of almost all ivies are black but a form of helix called poetarum produces orange berries. If you buy one so named it takes a long time to find out whether you have been cheated.
Ivies climb by means of adventitious rootlets which form when young growth touches the support. The tip of the rootlet then forms an adhesive pad. Old growth will not produce rootlets so if a branch falls off a wall you can’t stick it back. The rootlets cannot absorb food or water so if you cut the plant off at the bottom it will die. It follows that ivies are not parasitic, they do not feed off host plants nor off bricks of a wall. The only circumstance in which they damage a structure is if there are cracks and holes filled with a medium conducive to rooting. When ivies are planted on soil then real roots are formed at the leaf nodes and this obviously aids the colonisation of more space.
The species ivies all have the habit known as vining which means they throw out long trails with little branching. In 1921 a mutation from H. helix occurred which had thinner leaves and a very branching habit. Pittsburgh as it was named gave rise to a new race of ivy – those with a self branching habit – which made the use of ivies as pot plants and topiary possible.
Although they do not look hairy, ivies have minute hairs on young shoots and leaf petioles and to a minor degree on the leaves. The significance of these hairs is that they differ between the species and are a great aid to identification.
In Britain, H. helix and many of its clones can be considered hardy but some of the thinner leaved, self branching house plant ivies are less so. How well they survive outdoors depends on location and situation. In the relative warmth of recent years we have not had one die at Brownhill House. The other species are also generally hardy in Britain except for H. canariensis which just about tolerates the southern counties.
CULTIVATION
Ivies are tolerant of a wide range of soil types but prefer neutral or slightly alkaline conditions. The best growth will be obtained with a moist soil but it must not become waterlogged. Ivies are originally woodland plants and prefer shady conditions, however, they will stand rather more sun than is often thought and the variegated clones generally need light to maintain their colour. Nevertheless, sun baked banks and south walls are not the places for ivies.
No special precautions are needed when planting but spring is the best time and there is advantage in planting deeply. Ivies often "sit still" for some time before romping away.
In the garden little or no feeding is necessary in most situations but in containers and baskets a general purpose "balanced" fertiliser is suitable.
Ivies are less prone to pests and diseases than many other plants, and this is another of its virtues. However, they can be attacked by mites, aphids , scale insects and vine weevil and also various leaf spots and mildews. The usual precautions and remedies should be taken.
The shape and size of plants can be readily controlled by clipping or by using secateurs.
Ivies in the juvenile form root fairly readily and the usual mode of propagation for amateurs is either by semi ripe nodal cuttings in June or stem cuttings placed in a cold frame in October. Not surprisingly, layering works well.
USING IVIES
Basically, you can put them almost anywhere. The main situations are to climb walls or any other structure, as ground cover and to trail out of containers. It is of course necessary to select a clone of suitable leaf size, vigour and habit for the particular situation.
"Structures" can include old tree stumps, garden sheds, discarded motor cars, fences and purpose made pillars. When grown on a fence the result is termed a fedge. "Pillars" can be of various shapes and any size, including small structures for indoor plants in pots. By using frames of wire or other convenient material, either stuffed with moss or open, complex topiary can be created, both indoors and out.
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