Climbing plants on a pergola

A pergola covered in a climber is the picture many people have in mind. It is also the setting where a light kit frame can struggle most. A mature climber adds weight, holds water against the timber and catches the wind like a sail. None of that is a reason not to plant. It is a reason to choose the frame, the plant and the fixings with care.

What a climber does to a pergola

• Weight. A young plant weighs very little. Some vigorous climbers become heavy and woody over the years, and a wet canopy weighs more than a dry one.
• Wind. An open frame lets wind through. A dense climber turns the top and sides into a solid surface, so the frame and base carry more wind load.
• Moisture. Leaves keep the timber shaded and damp. Stems wrapped round a post trap water against it.
• Movement. Twining stems tighten as they thicken. They can push joints apart, lift a rafter or wrap round fixings.

We do not give safe loads or plant spacings here. They depend on the frame, the plant and the site, and no single figure covers them.

Check the frame before you plant

• Read the maker's instructions. Some kit makers say whether climbers are suitable. If they say nothing, ask them in writing.
• Look at the section sizes. A light timber kit is a different proposition from a heavy-section frame built for a garden walk.
• Check the base. Posts on spikes or light pads are more likely to rock as the plant grows. The wind and snow guide explains why extra surface area matters.
• Roofed pergolas. A climber over a louvred or fixed roof can stop blades closing, block gutters and hide damage. Most makers of those roofs do not expect plants on top. See the roof types guide.

Timber or aluminium

Timber frames are the traditional choice for climbers, but they are the ones most at risk from damp. Aluminium does not rot, though plants can scratch powder coating and trap dirt in the joints. A light aluminium kit may also not be designed for the extra weight. The aluminium or timber guide compares the two materials more broadly.

Plant it so the timber can breathe

• Plant a little away from the post, not hard against it, and lead the stem to the frame.
• Use wires, trellis or ties so the plant climbs a support rather than wrapping the post itself.
• Keep soil, mulch and gravel off the post base, where rot starts.
• Do not water against the post. Water the root area, not the timber.
• Use ties that will not cut in as stems thicken, and loosen them each year.

Keep on top of it

A climber that is left alone for a few years can be hard to bring back without damaging the frame. Once or twice a year:

• cut back growth that wraps round fixings, rafters or joints
• thin out dense growth so air moves through and the timber dries
• look at the post bases and joints for soft timber or movement
• check ties and wires.

The timber pergola maintenance guide has a fuller annual check. If a post base is already soft, see repairing a rotten pergola post.

If you already have a mature climber

Do not cut away a well-established plant in one go without thinking about the frame. Some old pergolas are partly held together by the plant, and cutting it back can show just how much damage is underneath. Look carefully, prop the frame if needed, and get a carpenter's view if the posts or joints are soft.

Which climbers are best for a pergola?

That depends on your soil, the aspect and the frame. A garden centre or a horticultural society can advise on plants for your site. Tell them how strong the frame is, and choose a plant whose vigour suits it.

Will a climber void my pergola guarantee?

It might. Some timber guarantees expect the product to be maintained as instructed, and damage caused by plants may not be covered. Read the terms or ask the maker.

Can I grow a climber up an aluminium pergola?

Often, if the maker allows it. Use ties and supports rather than letting the plant wrap round the frame, and check that it does not interfere with any roof or moving parts.