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Poplars

Kathrin Hofmeister Kathrin Hofmeister

Everyone of us has probably heard the rustling of poplar leaves. With our tips on planting and care, Poplars will also thrive in your garden.

Origin

Poplars owe their botanical name Populus to the ancient Roman name for poplar. The genus with around 40 species grow in the northern temperate zone and is closely related to the willow tree. Both belong to the willow family (Salicaceae). In the past, Poplars were used to drain swampy areas because the trees, thanks to their extensive roots, can draw a lot of moisture from the ground and quickly evaporate through the mighty crowns. Native species such as the black Poplar (Populus nigra) growing in riparian forests, but also the (Populus tremula) were considered beneficial and used as medicinal plants in ancient times. An anti-inflammatory and analgesic ointment was prepared from the leaf buds. Similar to the willow tree, poplars contain an anti-inflammatory substance that is chemically similar to salicylic acid. Because of their rapid growth, poplars, especially the Canadian poplar (Populus x canadensis), are important for timber production.

Appearance and Growth

Poplars grow fast. Most species and forms develop into large imposing trees between 65.61 and 131.23 feet high. Even the smallest representatives of the aspens reach around 49.21 feet high. They can develop large-domed and broadly spreading crowns like the black and gray poplar (Populus nigra and Populus x canescens) or the narrower crown of a (Populus balsamifera). The columnar shapes remain slim, such as the Lombardy poplar ‘Italica’ (Populus nigra ‘Italica’) or the quaking aspen (Populus tremula).

White Poplar (Populus alba)

The white Poplar (Populus alba) grows into a mighty tree up to 65.61 feet high

A special feature of the genus Populus is the formation of so-called clone colonies. From the roots of a tree, saplings grow in a radius of up to 131.23 feet. Since it is a kind of vegetative propagation, all growing trees around the mother plant have the same traits. Behind the strategy lies an ingenious move by nature: If the tree perishes, for example in a storm or fire, it will continue to grow from the roots. On the other hand, poplars displace other plants easily due to their runners. Keep this in mind when choosing your planting location!

Leaves

Poplars have oval-shaped to triangular, sometimes heart-shaped leaves. Only the quaking aspen (Populus tremula) has rounded leaves. The maple tree leaves resemble the leaves of the white Poplar (Populus alba). It is lobed. Other species such as the black poplar have serrated edges.

The rustling of the Poplars is its distinguishing feature. In the case of the quaking aspen, also known as aspen, the reaction to the slightest breeze is so pronounced that one speaks of "trembling like aspen leaves". Any breeze can flutter poplar leaves so easily because the leaves hang from a long, flattened petiole. The leaf stalk helps to distinguish the native black poplar from the Canadian black poplar hybrids (Populus x canadensis). The hybrids have glands at the transition to the leaf, the black poplar do not. In some species, the underside of the leaf is slightly hairy. This is conspicuous in the white poplar (Populus alba ‘Nivea’), which is white on the underside.

Leaves of the quaking aspen

The leaves of the quaking aspen rustle at the slightest breeze

The winter buds made up of several scales are typical of all poplars. Often these leaf buds are covered in a sticky resin. In some species, like the balsam poplar (Populus balsamifera), it smells intensely balsamic. The active salicin and populin in it, as well as essential oils and tannins, are used in the "poplar ointment" for burns and inflammations. collect the resin and convert it into . They use it to cement their honeycombs to protect them against intruders and diseases. The germicidal and immune-boosting effects are also being researched in medicine. Several native butterfly caterpillars feed on poplar leaves.

Flowers

Poplars bloom in March and April. They have catkin blooms. Although they hang down, the catkins are hardly noticeable because they usually bloom high up in the tree. The female catkins have short-stalked ovaries, are yellowish green and often slightly longer than the male flowers. The male catkins are between 0.78 and 3.93 inches long and, like the black poplar, can be reddish purple in color. The flowers are predominantly dioecious. That is: There are male plants with only male flowers and female plants with only female flowers. The Berlin poplar (Populus x berolinensis), for example, or the Lombardy poplar (Populus nigra ‘Italica’) are purely male. Poplars are usually an important source of nutrients for insects.

Poplar flowers

In March and April, poplars form pendent catkins

Fruit

Two to four-lobed fruit capsules form from the female fruit catkins. If the capsules open in May and June, they release woolly white seeds. The wind can carry the seeds, which are equipped with silky hair that assist in being carried by the wind, up to 31 miles.

Location and Soil

Poplars are undemanding when it comes to the planting location and can be planted in sunny to shaded locations. The genus Populus prefers moist, nutrient-rich and well-aerated soil, but all species are very adaptable. The gray poplar can even cope with waterlogged, boggy locations. A white poplar can even adjust to pure sand, if need be, and adapts to the circumstances by growing shrub-like. However, poplars are always in search of water and can damage drainage systems if their roots penetrate drainage pipes.

Populus nigra ‘Italica’

Columnar shapes, Populus nigra ‘Italica’, are often planted on river banks

Planting

As is the case with most woody plants, fall is the best time to plant. Dig out the planting hole at least twice as deep and wide as the size of the root ball. After planting, you need to water the plant well. For stabilization, a support post must be used so that the tree can grow in well.

Care Tips

Black poplars are robust trees that can withstand a lot. They are also particularly hardy.

Pruning

Poplars don't need pruning. However, they can become brittle with age. Then you should check the crown regularly and remove unsteady sections if necessary.

Where to plant

Because of their size, poplars are mainly planted in the open countryside and in parks. In gardening and landscaping, they are used to fortify banks and embankments. As a street and avenue tree, people like to plant columnar shapes such as the Lombard poplar ‘Italica’. The narrow-crowned forms are also used in rows as wind breakers to enclose orchards. The birch poplar (Populus simonii) can sometimes be seen in urban areas. With its long overhanging shoots and glossy green leaves, the species is particularly picturesque. It tolerates heat very well and can withstand the effects of climate change.

Important Species and Varieties

The white poplar ‘Nivea’ (Populus alba) attracts us with its silvery sheen. It is particularly effective in windy conditions because the underside of the leaf is covered with a silvery-white felt. The balsam poplar (Populus balsamifera) catches the eye with its balsamic scent when the leaves are sprouting. A cross between the poplar laurel (Populus laurifolia) and the columnar shape of the black poplar (Populus nigra ‘Italica’) is the Berlin laurel poplar (Populus x berolinensis) with a relatively slender crown. The native black poplar (Populus nigra) is endangered and is protected. It is being displaced, among other things, by black poplar hybrids, which provide even faster-growing timber. The Canadian poplars (Populus x canadensis) are therefore also called timber poplars.

A selection from the crosses between the European black poplar and the American black poplar (Populus deltoides) is the ‘Robusta’ variety with annual growth of one to 3.28 to 4.9 feet when young. The purple poplar ‘Purple Tower’ (Populus deltoides) is a new type of poplar with deep red leaves. It keeps the red leaf color throughout the summer. The large leaf poplar (Populus lasiocarpa) has particularly large leaves. The heart-shaped leaves are 6.69 to 9.84 inches, sometimes even 11.81 inches long. The birch poplar (Populus simonii) impresses with glossy green foliage that is fresh light green very early on. The quaking aspen (Populus tremula) offers a particularly beautiful fall color in apricot colors. But the aspen is not only an attractive deciduous tree at the end of the season. Due to its medium size, it is also suitable for smaller areas. The quaking aspen (Populus tremula ‘Erecta’) is an option if it becomes too expansive. The American counterpart to the native quivering poplar is the American aspen (Populus tremoloides).

Propagation

Poplars and their varieties are best propagated vegetatively using cuttings or runners. Poplars cross easily, so different characteristics may come to light when sown.

Diseases and Pests

Poplars are attacked by predators such as longhorn beetles. For example, the columnar poplar ‘Italica’ is particularly susceptible to the poplar longhorn beetle. Freshly planted, young trees have to be protected against being eaten by grazing animals in the first few years. After several years of infestation, leaf fungus diseases result in shoot tip disease and can lead in the long-term to bark death. The pathogen for bark blight on poplars is Cryptodiaporthe populea. Some species can get bark cancer.

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