Ivy on Walls

Harm to historic masonry and buildings

Ivy growing on or into a wall can cause problems. These include:

• Dislodging masonry, mortars and pointing
• Lifting copings and slates
• Blocking gutters and downpipes
• Growing into windows and roof spaces
• Masking buildings and hiding architectural features
• Concealing underlying problems, such as damp
• Hindering maintenance works
• Swamping smaller structures, such as grave monuments
• Destabilising the upper parts of vulnerable structures, such as ruined or free-standing walls, owing to additional weight and wind action
• Harbouring pests, such as mice

Climbing and rooting of ivy

Ivy climbs structures to gain more sunlight, using the surface as a climbing frame. It has 2 types of woody stems: creeping and climbing stems, and flowering stems. The creeping and climbing stems grow aerial attachment roots. The flowering stems, usually high up on the plant, are non-clinging and may grow to more than 3 metres long. The evergreen leaves are either the 5-lobed juvenile leaves on the creeping and climbing stems, or the unlobed heart-shaped adult leaves on flowering stems.

How do aerial roots attach to walls?

Research published by the Royal Society shows that the attachment process is complex. As ivy begins to climb, it is triggered to adapt its aerial roots (also called attachment or adventitious roots) to fit the surface and increase their contact with the wall. Tiny hairs grow on the aerial roots, and they secrete a chemical to help them stick to the surface. Attachment is further strengthened by hook-like growths on the root hairs. These root hairs then dry out into spiral shapes, which lock the ivy onto the wall.

Although the attachment is remarkably strong, it is entirely superficial. The attachment roots do not penetrate the masonry material or extract moisture or nutrients from it. However, ivy will often grow along eroded mortar joints, probably to seek protection against desiccating winds.

The attachment system continues to work even when ivy is dead. If you cut ivy at the base, and leave it to die, the wall surface will still be marked when you pull the ivy away. Cutting ivy at ground level in an attempt to kill it off is not recommended. It may lead to rooting-in problems higher up the wall.

How does ivy root into walls?

The small aerial roots that grow on ivy stems attach the plant to the surface of the wall only. They do not root into the wall, or grow bigger with time.

In some circumstances, 'proper' roots are produced, usually at leaf nodes. This may occur if the base of the plant is cut, if a wall is very damp or if there is organic matter, like leaf litter, from which ivy can extract nutrients. These roots can penetrate the structure via any small crack or hole. Under suitable conditions, the roots will grow in size and number, and may disrupt masonry. They can spread deep within the structure causing physical and mechanical damage over time.

Where a stem of ivy has formed proper roots and grown up through existing cracks or holes in the structure, damage will worsen as the ivy increases in girth each year. When properly rooted ivy is like any other tree or shrub growing in a wall, and damage will escalate until it is removed.

When is heavy ivy growth a problem?

If ivy reaches the top of a structure and starts to produce arboreal or flowering growth, it will become increasingly large and heavy, especially when wet. It can act as a sail in windy conditions and destabilise sections of masonry. Cutting back the flowering stems can reduce the problem, although these will regrow unless spot-treated with herbicide.

Further information