They produce extensive root systems that tend to invade drains so they should not be close to buildings.
There are several well-known trees in the genus. P. tremula Award of Garden Merit (AGM) is the woodland tree, aspen, sometimes called the quaking aspen because the leaves quiver in the slightest breeze. Its wood is used to make matches. Then there is P. nigra ‘Italica’ AGM. The outline of the Lombardy poplar is unmistakable with its tall, slender silhouette.
Its parent P. nigra, the black poplar, is facing a fight for survival in the UK. A European native, it suffers from the success of its progeny, which hybridise readily with existing trees, of which there were reported to be only 2,500 in 2010. Of these, only 400 are female trees. They are seen as a nuisance because of their fluffy seeds. Back poplars have a tendency to become chlorotic and can therefore be short lived.
The black poplars and their hybrids may have their problems but they have lovely, coppery
juvenile leaves. The foliage of the balsam poplars produces a pleasing fragrance as it unfurls in the spring. The white poplar has distinctive leaves with attractive white felty undersides and many of the species have long catkins that decorate the bare branches of the trees in spring.
When choosing a poplar, clearly the height and potential size of the root system are the characteristics to consider above all else. They are generally fast-growing, but vary in height.
The tallest is between 20m and 35m (Lombardy poplar and the Western balsam poplar, P. trichocarpa) and the smallest are around 10m (P. alba ‘Raket’ and P. tremula ‘Pendula’).
Several of the poplars produce suckers, so this needs to be considered when planting. The aspen is one of these, so what appears to be a woodland of a hundred trees could be an ancient, original tree surrounded by its numerous suckers. There is such a tree in Chepstow, Wales, which, with its suckers, covers an entire hectare.
Other suckering types include P. balsamifera, P. alba and the not fully hardy P. szechuanica var. tibetica, which can be coppiced to produce attractive purplish-brown young branches, clothed in red-veined and silvery-backed leaves.
They generally thrive in most types of soils, except shallow chalk, and will cope with wet and boggy sites. They are tolerant of air pollution and some do well in coastal areas. But some species and their hybrids are susceptible to canker.
What the specialists say
Mike Glover, managing director, Barcham Trees, Ely
"All the poplars we stock have superb merit but only if they are put in a suitable location. Trees often get a bad press for a series of faults but it is their placement that is usually the problem, not the tree itself. Poplars have aggressive and expansive root systems so they are suited to rural locations, well away from buildings.
"They make superb screening or windbreak trees and will generally thrive in wetter soils where other genera struggle. By default, most landscaping schemes are for urban areas or for beautifying dwellings. Therefore, poplars are rarely suited for this purpose.
"My favoured poplar is P. tremula ‘Erecta’. It’s a fabulous tree with a distinctive architectural habit, great autumn and spring colour and flickering leaves, even on the stillest of summer days, that sound like running water. It will grow pretty much anywhere but is best placed away from buildings due to its vigorous root structure."
Kevin Croucher, managing director, Thornhayes Nursery, Devon
"Poplar is an excellent tree in the right place and can be very attractive. As for the species, P. alba is an attractive tree and useful as shelter on exposed coastal sites. P. × canadensis ‘Aurea’ AGM is a striking, large gold-leaved form for a rich, moist site.
"P. tremula ‘Pendula’ AGM is a splendid large weeping tree with excellent lamb’s tail catkins in
spring and rich gold autumn colour. My favourite is P. trichocarpa ‘Fritzi Pauley’, which is a vigorous, fast-growing canker-resistant balsam poplar that smells wonderful on
the moist spring air when breaking into bud.
"It is important to ensure that poplars have a site with adequate space, as they develop large root systems, and suitable soil. Some will tolerate dry sites, but most need rich, moist, not waterlogged soils."
Robert Player, proprietor, Garden Associates, Central London/Hertfordshire
"We maintain private squares in Kensington and Westminster and we are seeing white poplars in old gardens around Maida Vale that were planted in the late 1800s starting to drop like flies. Poplars are known for not being long-lived and this is probably due to their fast-growing nature and their tissue make-up — after all, they are used for ‘soft’ wood items such as tomato boxes and matches.
"While I would not recommend any of the larger poplars for urban areas, certainly not near buildings, there are a few on the market that could be used in normal suburban gardens. P. × canadensis ‘Aurea’ AGM is a lovely tree. It has cream and green variegated leaves that are often tinged pink.
"Even more exciting is P. deltoides ‘Fuego’. It has large, burgundy-copper leaves and square burgundy stems. It looks to be a good specimen for coppicing. I saw a specimen in the borders at Great Dixter recently, so I think head gardener Fergus Garrett must have the same idea."
Species and varieties
P. alba, or the white poplar, is a large tree with a fairly rounded form. The undersides of its green leaves are felty and silvery-white, and they turn yellow in the autumn. A fast-growing tree that needs space to develop its large root system. Ideal for exposed and coastal positions and on calcareous soil. Height: 20m.
P. alba ‘Raket’ is a smaller than normal poplar, with an upright, narrow habit. Its leaves are dark-green with white undersides and they turn yellow in the autumn. Height: 7m. Spread: 2m.
P. ‘Balsam Spire’ AGM (H4) is considered the best balsam poplar. It is so named because of its fragrant leaves, which smell strongest as they unfurl in the spring. It is a slender, upright tree with thin branches and has large, heart-shaped leaves that have a pale-green underside and turn yellow in autumn. It has a strong suckering habit. Height: 20m.
P. × canadensis ‘Serotina’ was the earliest commercial poplar resulting from a cross between the European and the American black poplars. The name ‘Serotina’ refers to the lateness of the foliage unfurling. It has now been superseded by more productive clones. Height: up to 35m.
P. × canadensis ‘Aurea’ AGM (H4) is the golden poplar. It is fast-growing, becoming a large tree, with a rather uneven crown. Its juvenile leaves have a coppery red colour and it bears catkins with conspicuous red anthers. Recommended as a parkland tree. Height: 25m.
P. nigra, or the black poplar, is now rarely seen in the UK despite being a European native. There are projects in different parts of the country attempting to propagate from existing male and female trees and to bulk up numbers. If found, it is a large, rounded and heavy-branched tree, with a burred trunk and glabrous twigs. A majestic tree in park and woodland settings. Height: 20m.
P. nigra ‘Italica’ AGM (H4), or the Lombardy poplar, is a classic tree used to create windbreaks and screens in rural locations. It is tall, tightly columnar and of uniform habit, making it ideal for avenues. A tough tree that copes well in windy and coastal locations. Height: 20m.
P. tremula AGM (H4) is the common or quaking aspen. It is well-known in UK woodlands and parks with its green, rounded leaves with wavy edges that "quake" in even a light wind. They appear late in spring and hang on late into the autumn when they turn a clear yellow. Height: 15-20m.
P. tremula ‘Erecta’ is a variety that is tightly columnar, so it is like a smaller version of the Lombardy poplar. However, it offers more seasons of interest because its foliage emerges bronze in the spring, following long catkins. Then the leaves turn orangey-yellow in the autumn. Works well in an urban environment because it requires little maintenance. Height: 15-20m.
P. tremula ‘Pendula’ is a graceful weeping form of the common quaking aspen. It produces long purple catkins in February. Its leaves turn a buttery yellow in the autumn and persist on the tree. Height: 10m.
- Thank you to Floramedia, which supplied the images for this article from its photo library