Poplar - Populus: Planting, Growing and Caring

Botany and description

Poplars belong to the Salicaceae family, just like willows. The genus Populus includes 35 species distributed across the northern hemisphere. In addition to the species, humans have created a large number of hybrids and cultivars. Contrary to popular belief, the genus name Populus does not come from the Latin “populus” (people), but rather derives from the Greek “papalein” (to tremble), referring to the characteristic trembling of poplar foliage.

The most common poplar species are:

• Populus alba or White Poplar: this tree grows up to 25 m tall. The foliage has a whitish, downy underside. It tolerates drought, sea spray, and poor, calcareous soil;
• Populus X canescens: a hybrid between the White Poplar and the Aspen. It has a rounded crown and can reach 30 m in height;
• Populus deltoides or Eastern Cottonwood: native to North America, this is a tough tree, but unfortunately short-lived and very brittle in strong winds;
• Populus fremontii: native to North America, it tolerates drought and extreme cold well;
• Populus lasiocarpa: a very attractive poplar with foliage veined in red and light green. It grows more slowly than its cousins and reaches only about 10 m in height;
• Populus maximowiczii: an Asian species whose pubescent young shoots take on a beautiful red hue;
• Populus nigra or Black Poplar: a large poplar (30 m tall or more) with dark bark. Its cultivar ‘Italica’ (synonym ‘Pyramidalis’) is very famous and widely planted;
• Populus tremula or Aspen: a medium-sized poplar (15 m tall), but vigorous and very suckering. Its thin, flattened petioles make the foliage “tremble” at the slightest breeze;
• Populus tremoloides or Quaking Aspen: a North American poplar with finely toothed foliage that also trembles at the slightest breeze;
• Populus trichorpa or Balsam Poplar: a poplar native to the western United States. It tolerates sea spray very well. It is characterised by highly fragrant young wood;
• Populus yunnanensis or Yunnan Poplar: native to Yunnan, this is a very beautiful poplar with reddish-veined foliage. It also resists heat and drought well.

Populus alba – Populus nigra – Populus tremulus

Populus alba – Populus nigra – Populus canescens

The cultivation of poplars is called poplar farming, and foresters who manage poplar plantations are poplar growers. A poplar plantation is called a poplar grove.

Poplars grow very quickly. These trees have therefore been widely planted along roads, canals, or as windbreaks. Poplars do not live very long: an average of 60 years. However, the Black Poplar (Populus nigra) can live for several hundred years. The rapid growth of poplars is sometimes a drawback: the wood is soft and breaks easily in the wind. Never stay near a poplar during a storm! (and, if possible, avoid trees when it’s very windy!).

The root system of poplars is extensive, relatively shallow, but very spreading (like willows). It is therefore best to plant them very far away (at least 30 m) from any buildings or structures, to avoid damage to pipes or foundations. Because the root system is shallow relative to the tree’s height, poplars can fall quickly during a storm. Two good reasons not to plant poplars near houses.

Poplars are large trees, sometimes over 30 m tall. Their habit can be columnar (Populus nigra var. italica) or pyramidal. The foliage is deciduous and consists of simple, alternate, cordate or triangular or ovate and acuminate leaves (ending in a point). The leaves sometimes have a silvery underside. The leaves are attached by a long, flattened petiole. This compression contributes to the trembling of the foliage. The foliage often turns bright yellow in autumn before falling.

Cottony down containing the seeds that will be dispersed by the wind

When young, the bark is pale, almost white sometimes, becoming darker and more fissured with age. The wood is light and is used for making paper, matches, crates, plywood…

Like willows, poplars are dioecious species. This means there are distinct male and female individuals. The flowers appear as pendulous catkins in spring before the leaves. The male catkins are flexible with reddish stamens. The female catkins are stiffer. The pollen from the catkins is slightly allergenic for sensitive individuals.

The fruits follow the female catkins and form two-valved capsules containing cottony seeds. This cottony fluff allows the seeds to be carried by the wind or water. The cottony down from the seed capsules can also be allergenic.

The medicinal use of poplar is very ancient. The bark was used to combat fever. The buds and leaves were known for their diuretic and anti-rheumatic properties.

Poplars tolerate air pollution very well.

Our most beautiful varieties

Populus nigra Italica - Black Poplar

The famous Italian poplar is instantly recognisable by its very slender dark silhouette and almost columnar habit. This large deciduous tree reaches 30m in height with a 5m spread, developing a vertical trunk that continues up to the crown's apex, supported by multiple fine, nearly vertical branches.

• Flowering time April, May
• Height at maturity 30 m

See the product sheet

Populus tremula - Aspen

The Aspen is a large, fast-growing deciduous tree with a fastigiate, light and elegant habit. Its foliage trembles (quivers) at the slightest breeze, revealing the silvery underside of its leaves.

• Flowering time June
• Height at maturity 20 m

See the product sheet

Populus alba Nivea - White Poplar

Populus alba 'Nivea', called White Poplar or Silver Poplar, is a robust medium-sized tree. The underside of mature leaves is downy, while young shoots and leaves are strikingly white, giving the tree a shimmering silvery effect when stirred by the wind.

• Flowering time March, April
• Height at maturity 25 m

See the product sheet

Populus deltoides Purple Tower - Eastern Cottonwood

Populus deltoides 'Purple Tower' boasts remarkable foliage that changes from scarlet red to deep purple-black depending on the season, with contrasting blood-red main veins.

• Height at maturity 20 m

See the product sheet

Planting poplar trees

Where to plant?

The poplar is best planted in full sun.

Poplars thrive in deep, fertile soil that is fairly moist to wet. The White Poplar (Populus alba) tolerates waterlogged or conversely dry soils, whether calcareous or poor. The Aspen Poplar withstands sea spray well and can grow in sandy, poor soil.

When to plant?

In pots: in spring or autumn.

Bare-rooted: between November and December.

How to plant?

• Dig a large hole: about 1 m wide and 60 cm deep;
• Loosen the bottom of the hole well and set aside the excavated soil;
• Soak the rootball if potted or slurry the roots if bare-rooted;
• Place the tree in the centre of the hole;
• Backfill the hole with the excavated soil and firm well around the base;
• Water with 10 litres of water;
• Remember to stake the tree using three stakes arranged in a triangle.

Maintenance

Remember to provide a good watering can of water from time to time when the soil dries out during the first two years of cultivation. Additionally, a good mulch at the base of the tree will help keep the soil relatively moist.

Pruning involves removing dead, diseased or poorly placed wood. Prune the branches of poplars in winter, outside frost periods and before vegetation resumes.

Poplars in autumn

Diseases and Pests

The new poplar cultivars are generally quite resistant to diseases, but some ailments can still occur.

Poplar Canker

Poplar canker mainly appears north of the Loire in spring or autumn. This disease is caused by a fungus, Xanthomonas populi. It thrives in warm, humid conditions. The disease first manifests as whitish, then brownish, sticky oozing at the base of buds or lenticels. Cankerous lesions, forming irregular ridges, later appear on branches.

There are no treatments available. However, you can choose cultivars known for their resistance to the disease. It’s also advisable to prune only in winter and with tools thoroughly disinfected with alcohol.

Rust

Leaves are affected in spring when the weather is warm and humid: they discolour, then dry out and fall. The tree does not die but is weakened until new foliage appears.

→ To learn more about rust and how to get rid of it, follow Pascal’s advice.

Honey Fungus (Armillaria mellea)

Honey fungus is a mushroom that attacks weakened poplars. When symptoms become visible, it signals the tree’s relatively rapid decline.

→ Read our guide on Honey Fungus or root rot to learn more.

The Poplar Admiral Caterpillar (Limenitis populis)

This splendid butterfly was once considered a pest in poplar plantations. The caterpillar feeds on the foliage of the Aspen and other poplar species. However, this butterfly is now in sharp decline, nearly extinct in France and Belgium.

Propagation

The poplar naturally produces suckers from its running roots. It also self-seeds thanks to its multitude of seeds dispersed by the wind.

But the simplest way to propagate poplars remains hardwood cuttings.

• In November-December, take cuttings from the tips of branches (or stem sections) about 30 cm long;
• Plant them directly in the ground (the simplest method), or in a sand bed (moist sand) over winter until the cuttings develop roots;
• For those raised in a sand bed, transplant the cuttings into pots with compost in spring;
• Transplant them into open ground in autumn.

Poplar propagates so easily from cuttings that poplar growers commonly plant poplar poles – large stems of 1.50-2 m, about 20 to 30 mm in diameter. The lower end is trimmed at an angle, and the poles are driven 80 cm into the soil at a rate of 200 young plants per hectare. A few years later, the poplar plantation takes shape.

Association

It is challenging to suggest companion planting ideas for such large trees as poplars. Typically, poplars are planted in rows using the same essential oil.

However, let’s take the example of Populus deltoides ‘Purple Tower’, which could be coppiced annually. Its scarlet-red foliage tinged with purple will pair beautifully with other bushes and perennials featuring similarly toned leaves. Among bushes, a Physocarpus ‘Lady in Red’ as well as a Berberis thunbergii ‘Bagatelle’ would work perfectly. For perennials: a few Heuchera ‘Forever Red’ will thrive under the beneficial shade provided by the bushes and the poplar.

Too red-purple for your taste? Very well! In that case, opt for a striking green-yellow contrast to highlight the foliage of the poplar and other plants. For this role, the Catalpa bignonioides ‘Aurea’ will be ideal with its large green-yellow leaves. The substantial size of its leaves will complement the foliage of the ‘Purple Tower’ poplar splendidly. You can coppice the Catalpa annually as well.

Populus deltoides ‘Purple Tower’, Catalpa bignonioides ‘Aurea’, Berberis ‘Bagatelle’, Heuchera ‘Forever Red’

Anecdotes

• France is the leading exporter of poplar wood and ranks second worldwide;
• It is said that Emperor Napoleon I introduced the Lombardy Poplar to France as a roadside or canal-side tree;
• For the druids, the poplar symbolised old age due to the silvery underside of its leaves;
• Ancient literature (Greek and Roman) regularly mentions poplars.