Balsam poplar

How to recognise it

Habit

Large tree of 20–25 m, sometimes taller in its homeland, with a narrow to egg-shaped crown and upswept branches. Bark smooth and grey-green at first, later dark grey and deeply furrowed. Produces root suckers.

Leaves

Alternate, oval to broadly lance-shaped, 7–12 cm, with a long tip and a finely scalloped edge. Glossy dark green above, pale whitish green below, often with rusty brown resin spots. Leaf stalk round, not flattened. Yellow in autumn.

Buds

Large, up to 2.5 cm, pointed, shiny reddish brown and sticky with a yellowish brown resin that has a strong balsam scent.

Flowers

Dioecious: male and female catkins on separate trees, in March–April, before the leaves. Male catkins reddish, female ones green. Wind-pollinated.

Fruit/Seed

Small capsules on long catkins, which split open in May–June and release many seeds with white fluff; only on female trees.

Confusion with

Black poplar and hybrid black poplar: triangular leaves with a flattened leaf stalk and less fragrant buds. Aspen: round leaf with a wavy edge and a flattened stalk. Western balsam poplar: very similar, but with larger leaves and hairy capsules that split into three parts instead of two.

Flowering: March–April · Pruning: July–August

Why grow it?

• The sticky buds smell wonderfully of balsam in April and May, especially after a shower and on warm, still evenings.
• Honeybees collect the resin from the buds to make propolis, the glue they use to seal their hive.
• Poplars are food plants for the caterpillars of, among others, the poplar hawk-moth and the puss moth.
• Grows very fast: within a few years you have shade or a windbreak, even on wet ground where few other trees will grow.
• Woodpeckers easily dig nest holes in the soft wood of older trees, which tits and other hole-nesters use later.
• Fresh yellow autumn colour in October.

Balsam poplar: where does it grow best?

• In the wild: banks of rivers and lakes, floodplains and wet hollows in the northern conifer forest, often with willows and birches.
• Full sun: as a pioneer it tolerates little shade.
• Moist to wet, fertile soil: clay, loam or sand with a high water table. It copes well with short floods; on dry sandy soil it struggles.
• Only for a large garden, a park or a farmyard: keep well away from houses, sewers, drains and ponds, at least as far as the tree will grow tall.
• Good as a windbreak at the edge of a meadow or farmyard, alone or in a row.

Goes well with

• Alder: Likes the same wet ground; in winter siskins eat the seeds from its cones.
• White willow: A fast native partner along ditches and ponds, and food plant for the same caterpillars.
• Elder: A shrub for the edge of the canopy, with flowers for insects and berries for birds.
• Meadowsweet: Fragrant creamy white plumes in summer, on the same moist soil.
• Yellow flag: Yellow flowers at the edge of a nearby pond or ditch.

Balsam poplar: when and how to plant it?

1. Buy a young tree or a whip from a tree nursery. Never take plants or suckers from the wild or from someone else’s planting.
2. Ask the nursery for a male tree: it produces no fluff. Poplars are grown from cuttings, so the sex of a plant is usually known.
3. Plant while dormant, from November to March, when the ground is not frozen; bare-root trees establish best then.
4. Dig a hole well larger than the roots, set the tree at the same depth as before and firm the soil well.
5. For a larger tree, drive in a stake at an angle on the windward side and tie it with a broad strap, never with wire.
6. Water thoroughly straight away and during dry spells in the first year; on wet ground this is rarely needed.

Care

Water

In the first year, water well during dry spells. After that it looks after itself, especially on moist soil.

Feeding

Not needed: it grows fast enough already, and extra fertiliser only makes the wood weaker.

Suckers

Mow over suckers in the lawn; in borders cut them off as young as possible.

Safety

The wood is soft and brittle. Have a large tree checked every few years for dead wood and weak branches, especially next to paths or a patio.

Fluff

Female trees release lots of white fluff in May–June; it can clog pond filters, gutters and air vents.

Tip: When buying, ask specifically for a male tree: its buds are just as fragrant, but it will not send white fluff drifting through your garden in June.

Pruning and mowing

Pruning months: July–August.

When: In July–August, when the tree is in leaf and wounds close quickly. Avoid spring, when the sap is rising.

How:

• Young tree: choose one central leader and remove competing tops.
• Raise the crown gradually: remove a few of the lowest side branches each time, never more than a quarter of the crown in one year.
• Remove dead, broken and rubbing branches just outside the branch collar, without leaving a stub.
• Leave large, old trees to a qualified tree surgeon.

Caution: Large pruning wounds heal poorly and let in rot and canker. Prune a little and often rather than a lot and rarely, and never top the tree.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Hardwood cuttings

Very easy: in January–February cut 20–30 cm lengths of one-year-old shoots and push them two thirds of their length into loose, moist soil. They root by themselves in spring.

Suckers

In winter, dig up a sucker with a piece of root and replant it elsewhere.

Seed

The seed stays viable only briefly. Sow it straight away in May–June on wet, bare soil; it germinates within a few days.

Balsam poplar: how does it get through the winter?

Hardy to −45 °C.

• Deciduous: after its yellow autumn colour it stands bare, with striking, shiny, sticky buds.
• Extremely hardy: in its homeland it survives temperatures of −45 °C and colder.
• On mild days in late winter you can sometimes already smell the balsam scent of the swelling buds.
• Holes in old trees are a winter roost for tits and woodpeckers.

Diseases and pests

• Canker: Cracks, swellings and sunken patches on the trunk and branches, sometimes oozing. Cut out affected branches in summer and clean your tools between cuts.
• Rust and leaf spot: Small orange or brown spots on the leaves in late summer, caused by fungi. Harmless to a healthy tree; clearing up the leaves helps.
• Branch failure: The soft, brittle wood breaks in storms. Have old trees checked and do not plant it next to a house, a car park or a playground.
• Roots: The roots search for water and can grow into sewers and drains or lift paving. Keep a good distance when planting.
• Suckers and fluff: Mow suckers in the lawn; avoid fluff by choosing a male tree.

Through the year

• January: Dormant. Take hardwood cuttings. Plant in mild weather.
• February: Take hardwood cuttings and push them straight into the ground. Planting.
• March: Catkins flower on the bare branches. Last chance to plant bare-root trees.
• April: Leaves unfold; the sticky buds smell strongly of balsam.
• May: Female trees release white fluff. Sow seed straight away.
• June: Last fluff. Cut off suckers. Look for poplar hawk-moth caterpillars.
• July: Pruning: remove dead wood and competing tops.
• August: Pruning still possible. Water young trees in dry weather.
• October: Yellow autumn colour.
• November: Leaf fall. Plant bare-root trees.
• December: Dormant. Plant in mild weather.

Did you know?

• Balsam poplar is one of the most northerly broadleaved trees in North America: it grows up to the tree line in Alaska and northern Canada.
• The species name balsamifera means ‘balsam-bearing’, after the fragrant resin on the buds. In North America the buds are also called ‘balm of Gilead’.
• In its homeland beavers and moose readily eat its bark and twigs.