Black poplar (Populus nigra) is a medium- to large-sized deciduous tree which can be naturally found in many alluvial European forests. It is a fast-growing tree, with a wide crown which is a common nesting place for different species of birds. Due to the degradation of its natural habitat, black poplar has become an endangered species in certain areas.
I. Appearance and Characteristics
Populus nigra, the black poplar, is a species of cottonwood poplar, the type species of section Aigeiros of the genus Populus. Black poplar has a large distribution area throughout Europe and is also found in northern Africa and central and west Asia. The distribution area extends from the Mediterranean in the south to around 64° latitude in the north and from the British Isles in the west to Kazakhstan and China in the east. The distribution area also includes the Caucasus and large parts of the Middle East.
Black poplars are medium- to large-sized deciduous trees, reaching 20–30 m, and rarely 40 m tall. Their leaves are diamond-shaped to triangular, 5–8 cm long and 6–8 cm broad, and green on both surfaces. Normally, their trunks achieve up to 1.5 m in diameter, but some unusual individual trees in France have grown old enough to have much larger trunks – more than 3 metres DBH (Diameter at Breast Height).
The species is dioecious (male and female flowers are on different plants), with flowers in catkins and pollination achieved by the wind. The black poplar grows in low-lying areas of moist ground. Like most other pioneer species, the tree is characterized by rapid growth and is able to colonize open areas quickly.
Cultivars
Several cultivars have also been selected, these being propagated readily by cuttings:
- ‘Italica’ is the true Lombardy poplar, selected in Lombardy, northern Italy, in the 17th century. The growth is fastigiate (having the branches more or less parallel to the main stem), with a very narrow crown. Coming from the Mediterranean region, it is adapted to hot, dry summers and grows poorly in humid conditions, being short-lived due to fungal diseases. It is a male clone. As a widely selected species chosen by golf architects in the 1960s, it soon became apparent that the poplar’s very invasive roots destroyed land drainage systems. Decades later, the same courses were removing poplar stands wholesale. Around 40 to 50 years, this short-lived variety starts shedding branches and is very likely to be blown over in high winds, each successive tree lost exposing neighbouring trees, creating a domino effect.
- Plantierensis group clones are derived by crossing ‘Italica’ with P. nigra ssp. betulifolia at the Plantières Nursery near Metz in France in 1884; they are similar to ‘Italica’ (and often mistaken for it), but with a slightly broader crown, and better adapted to the cool, humid climate of northwest Europe, where the true Lombardy poplar does not grow well. Both male and female clones are grown. This is the tree most commonly grown in Great Britain and Ireland as Lombardy poplar.
- ‘Manchester’ is a cultivar of P. nigra subsp. Betulifolia is widely planted in northwest England. It is a male clone, and currently seriously threatened by poplar scab disease.
- ‘Gigantea’ is another fastigiate clone, of unknown origin, with a rather broader, more vigorous crown than ‘Italica’. It is a female clone.
- ‘Afghanica’ (syn. ‘Thevestina’): most, if not all, specimens are of a single clone, and many botanists therefore treat it as a cultivar rather than a botanical variety. It is fastigiate, similar to ‘Italica’, but with a striking whitish bark; it also differs from ‘Italica’ in being a female clone. This is the common fastigiate poplar in southwest Asia and southeast Europe (the Balkans), where it was introduced during the Ottoman Empire period.
II. How to Grow and Care
A Lombardy polar tree is a popular choice when you want “living wall” privacy screens or windbreaks in a hurry. It comes at a price though; you can expect a lot of maintenance with this tree, Nurseries often sell only the male trees so you won’t have cottony seeds blowing around. However, the problem with male trees is that they produce abundant pollen, which can be allergenic.
As this tree has shallow, spreading roots, you should plant it away from pipes, septic tanks, lawns, gardens, sidewalks, streets, and foundations.
Sunlight
Black poplar is shade intolerant and needs full sun for its optimal growth. You need to plant it in a place where it can be exposed to sun all day and avoid light being blocked by buildings and trees.
Temperature and Humidity
The Lombardy poplar can be grown in a wide variety of temperate climates, including those where the winter low temperature is far below zero. In hot and humid climates, this tree is even more susceptible to Cytospora canker.
Watering
Black poplar thrives well in soils that are wet to semi-dry. Some species in genus Populus are more responsive to soils that are wet to moist, so water once a week is necessary during hot and dry weather. It is susceptible to pests and diseases in drought conditions. Black poplar is well adapted to regular watering during the initial years of plantation.
Soil
Black poplar doesn’t require special soils. It thrives best in deep, rich, well-drained soils, but can also grow in infertile and sub-irrigated soils. Organic matter is good for its growth while soil type and fertility are less considered when moisture is abundant. The ideal soil pH for it is 6.0-8.0.
Fertilizing
Black poplar responds well to fertilization at planting and during the initial years of its growth. Apply fertilizer with high nitrogen content and organic matter twice a year. Balanced compound fertilizer can also be used, such as 20-20-20(N%-P%-K%).
Planting Instructions
Site preparation is the most critical step as it can remove any rival vegetative cover and enrich soil physical conditions to enable root to grow. Fine tillage can be reached by cleaning up debris, raking and leveling the ground. Its root tends to be well-developed so a deep pit away from the house is needed. The spacing of planting has a great influence on the later growth of black poplar. It is recommended to keep the planting distance of 2 meters. Weed control is required in the first year of planting, as fierce competition can lead to black poplar death. Herbicides can be used before and after planting.
Pruning
Removal of the dead or diseased branches is needed immediately as they are prone to the variety of fungal and bacterial diseases. Winter is considered the best time to prune as black poplar is dormant and is free from mechanical injuries and stress. Pruning when plants are young can help them establish and thrive fast.
Propagation
Propagation of the tree is typically done from hardwood cuttings and not from seeds, which are not commonly available.
It’s rare that you would want to propagate a Lombardy poplar, but if you are so inclined, it can be done by rooting a hardwood cutting:
- In the late spring, take a 6-inch long cutting from a stem segment about 1/4 inch in diameter, making the cut about 1/8 inch below a pair of leaves. Pull off all the leaves on the lower half of the cutting, leaving 4 or 5 leaves at the top.
- Bury the bare end of the cutting into a 6-inch pot filled with a mixture of perlite and coarse sand. Water the pot and pack the mix tightly around the cutting.
- Place the pot in a shaded outdoor location and mist it several times a day to keep the leaves moist. Water the pot whenever the potting mix feels dry.
- After about two weeks, the cutting should be rooted; transplant it into a 6-inch pot and continue growing in a dappled shade location for two or three months until plentiful new growth is present. The sapling can be transplanted into a permanent garden location in the fall.
Potting and Repotting
Because of its vigorous and fast growth, Lombardy poplar is not suitable for container growing.
Overwintering
The tree is hardy to USDA zone 3 and does not need any winter protection.
Pests and Diseases
Common Pests & Plant Diseases
These trees are susceptible to borers, Cytospora canker, and bacterial wet wood, reducing their lifespan. Almost all of these trees develop stem canker disease by the time they are 15 years old. Long before they die, they may be disfigured by these pests and diseases, rendering them unattractive as landscape plants and necessitating their removal.
Common Problems
Lombardy poplars are short-lived, often succumbing within 15 years to a number of pests and diseases. For that reason they are best planted as a temporary solution in combination with a row of longer-lived screening plants such as Colorado blue spruce trees or arborvitae trees.
Removing the trees after they have served their purpose, however, can be problematic because they have an extensive, aggressively growing root system and they keep sending out suckers from their stumps even after they have been cut down.
III. Uses and Benefits
Black poplar is quite rare, particularly when it comes to the garden. The tree is very susceptible to disease and weather damage, making it rather unappealing, difficult to care for, and a litterer, infamous for covering lawns with debris. The black poplar can be used as protection from the wind, however, and provides some shade. It also has some ornamental appeal when planted in rows, though it doesn’t generally do well with other plants.
