Pergolas, made from timber uprights with crossbeams and laterals at the top, form an open-topped canopy for an outdoor eating area or walkway. When planted with vigorous, flowering climbers they make attractive structures in the garden, offering height, shade and additional colour.
Suitable plants for a pergola
Any rambler or strongly-growing climbing rose will be a good choice for a pergola. Rambling roses are particularly well suited since their long and flexible stems are easy to train up and over the structure.
Clematis that require little or no pruning and other vigorous, scrambling climbers such as summer-flowering honeysuckles are also a good choice.
Below are some suitable roses and climbers for pergolas;
‘Albéric Barbier’ AGM
‘Danse du Feu’
‘Easlea’s Golden Rambler’ AGM
‘Félicité Perpétue’ AGM
‘Francois Juranville’ AGM
‘Golden Showers’ AGM
‘Madame Alfred Carrière’ AGM
‘Madame Grégoire Staechelin’ AGM
‘New Dawn’ AGM
‘Phyllis Bide’ AGM
‘Sanders’ White Rambler’ AGM
Clematis macropetala (and cultivars)
Clematis montana (and cultivars)
Clematis tangutica (and cultivars)
Clematis tibetana subsp. vernayi (syn. orientalis hort.)
Clematis viticella (and cultivars)
Clematis of the Lanuginosa Group
Lonicera caprifolium AGM
Lonicera x italica AGM (syn. Lonicera x americana AGM)
Lonicera periclymenum 'Belgica'
Lonicera periclymenum 'Graham Thomas' AGM
Lonicera periclymenum 'Serotina' AGM
Celastrus orbiculatus Hermaphrodite Group AGM
Jasminum nudiflorum AGM
Jasminum officinale AGM
Jasminum x stephanense
Solanum crispum 'Glasnevin' AGM (in sheltered, milder gardens)
Solanum laxum ‘Album’ AGM (syn. S jasminoides ‘Album’ (in sheltered, milder gardens)
Vitis 'Brandt' AGM
Vitis vinifera 'Purpurea' AGM
Wisteria floribunda (and cultivars: 'Multijuga' AGM has the longest racemes)
Wisteria sinensis AGM (and cultivars)
How to build a pergola
Measurements for the uprights of a pergola should be around 2.7m (9ft) from ground level so that climbers can trail down to some degree without impeding passage.
The width across the path between the uprights should be approx. the same as the height to achieve a degree of balance. The space between posts within each of the two parallel rows can vary from 0.9–3.7m (3–12ft).
The best types of timber are larch, Douglas fir or oak. Pine is sometimes used, but tends to rot more quickly than other timbers.
Vertical supporting columns may need to be set 45–60cm (18in–2ft) into the soil. Treat their bases with a wood preservative and extend their life span further by placing 5–7cm (2–3in) of course gravel at the base of the hole, then setting the post inside a large drainpipe with the rim just above soil level, filling around with gravel and capping with cement.
Pergolas need to be of quite solid construction as they may be required to support a considerable weight of foliage, and when in open situations, withstand considerable wind buffeting. Upright should therefore be a minimum of 5x5cm (2x2in) and ideally 8x8cm (3½x3½in). The latter size would support crossbeams of up to 15x5cm (6x2in) and laterals of up to 5x2½cm (2x1in) at a spacing of around 60cm (2ft) apart.
How to plant and train climbers on a pergola
With larger pergolas a common practice is to plant two climbers near the base of each pillar, for example, a strong-growing climbing rose with a less vigorous clematis or honeysuckle, the rose providing additional support for the other climber. Strong-growing climbers such as Clematis montana ‘Rubens’ or wisteria will, in time, cover cross-beams and probably need some restriction.
Improve the soil at the base of the upright by forking in some garden compost or well-rotted manure. Plant clematis a little deeper than in the pot. Thoroughly water in. Cut back spindly stems to within 15cm (6in) of the ground to encourage shooting from the base.
When planting, angle the climber towards the support, using small canes if necessary to bridge the gap. Secure vertical wires or wire mesh up the pillar and tie in shoots to these as they grow. To cover the canopy quickly, train the shoots straight up the posts. Or, for flowering on the pillars, spiral the shoots around the posts. Continue to tie new shoots to the crossbeams and laterals until the pergola is well covered. Cut back overlong shoots with long-handled loppers.
Pillars may become bare at the base. To help overcome this, spiral any new shoots around the post rather than allowing them to go straight up. If there is no new growth to tie in, cut back one or two of the main stems in early spring to stimulate basal growth.
Overgrown plants on pergolas should be renovated in early spring.
Climbers that become dry at the roots will be susceptible to powdery mildew, especially honeysuckle and clematis. Keep young plants well watered in summer and mulch established plants with garden compost or leafmould each spring.
Large-leaved and evergreen climbers may suffer scorch from drying winds. These types of climber should be avoided if the pergola is in an exposed position.