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Herbaceous plant · Balsam family (Balsaminaceae)
Himalayan balsam
Impatiens glandulifera
In other languages: Reuzenbalsemien (Nederlands) · Balsamine de l’Himalaya (Français)
Grows wild in Belgium.
Himalayan balsam is a tall annual from the Himalayas that came to Europe as a garden plant in the 19th century and is now widely naturalised in Belgium along streams, rivers and ditches, in damp woods and on rough ground. It grows 1–2.5 m tall, with thick, translucent, reddish stems, lance-shaped leaves in whorls of three and pink to purple, helmet-shaped flowers from July to October. Ripe seed pods burst open at the slightest touch and fling the seeds several metres. It is an invasive alien species on the EU list: it forms dense, tall stands that crowd out native bankside plants. So never plant or sow it, and pull it up before it sets seed.
Caution: Invasive alien species on the EU list: never plant, sow or spread it, and never pass on seed. Pull it up before the pods ripen and dispose of plants with flowers or seed in a sealed bag with household waste, not on the compost heap.
Light
Sun or partial shade
preferably some sun
Moisture
Normal to wet
must not dry out
Hardiness
down to 0 °C
protect in harsh winters
Size
2 m
tall, 0.5 m wide
Flowering
July–October
| Pruning months | May–August |
|---|---|
| Height | 2 m |
| Native to Belgium | No, an invasive alien species |
| Flowering | July–October |
Identify
How to recognise it
- Habit
- Annual of 1–2.5 m, with a straight, thick stem and a shallow root system.
- Leaf
- Lance-shaped, 10–20 cm, finely toothed, opposite or in whorls of three, with small red glands at the base of the blade.
- Flower
- Pink, purple or sometimes white, 2.5–4 cm, helmet-shaped with a short spur, in clusters on long stalks in the leaf axils; sweet scent.
- Fruit/Seed
- Club-shaped seed pods of 2–3 cm which, when ripe, burst at the slightest touch and fling the seeds up to several metres.
- Stem
- Hollow, translucent and succulent, reddish, up to 3 cm thick, with roots at the lowest nodes.
- Confusion with
- Touch-me-not balsam is native, smaller (30–80 cm), with yellow flowers and alternate leaves. Small balsam has small, pale yellow flowers. Purple loosestrife has purple flower spikes and no helmet-shaped flowers.
Flowering: July–October · Pruning: May–August
In your garden
What you need to know
- Recognising it pays off: the earlier you pull it up, the less work you have later.
- It is on the EU list of invasive alien species: never plant or spread it.
- Dense stands crowd out native plants on banks and in damp woods.
- In winter it dies back and leaves bare banks that erode more easily.
- Its rich nectar can lure bumblebees away from nearby native plants.
- Fortunately it is easy to pull up: the roots are shallow and the seed stays viable for only a few years.
Himalayan balsam: where does it grow best?
- In the wild: banks of streams and rivers, ditches, damp woods, rough ground and wet verges.
- Grows in sun and partial shade, on damp, fertile soil.
- It does not belong in the garden: if it appears, pull it up straight away.
- Be watchful in gardens along a stream: seeds arrive with high water or with soil brought in.
Plant these instead
- Purple loosestrife: Native alternative: purple spikes at the water’s edge from July to September, rich in nectar for bees.
- Hemp-agrimony: Native alternative: pink flower heads in July–August, a butterfly magnet by the water.
- Meadowsweet: Native alternative: fragrant, creamy plumes in summer on wet ground.
- Yellow iris: Native alternative: yellow flowers in May–June at the water’s edge.
Maintenance
How to remove it
- Never plant or sow Himalayan balsam and never pass on seed: it is on the EU list of invasive alien species.
- Pull plants up from May to August, before the seed pods ripen. This is easy, as the roots are shallow.
- If pulling is not possible, mow or cut the stems below the lowest node, as low as possible; otherwise they regrow.
- Pile pulled plants without flowers or pods in a dry spot, roots upwards, so they cannot root again. Plants with flowers or pods go in a sealed bag with general household waste.
- Work from upstream to downstream and check again after 2–3 weeks for missed or late plants.
- Repeat for at least two to three years, until no more seedlings appear, and never carry ripe pods away on your clothes.
Control
- Pulling
- The best method: from May to August, pull up the whole plant with its roots, before the pods ripen.
- Mowing
- Mow large stands before flowering, as low as possible, below the lowest node. Mowing too high produces new side shoots that still flower.
- Disposal
- Plants without seed can dry out in a dry spot; plants with flowers or seed go in a sealed bag with household waste.
- Follow-up
- Come back after 2–3 weeks: late seedlings and missed plants flower into October.
- Native sowing
- After clearing, sow or plant native bankside plants so the bare ground is quickly covered.
Tip: Pull up Himalayan balsam in June, just before flowering: the plants are then big enough to spot them all, but they have no seed yet.
Pruning and mowing
Pruning months: May–August.
When: Pull up or mow from May to August, before the seed pods ripen.
How:
- Pull plants up, roots and all; they come out easily.
- Mow or cut below the lowest node, as close to the ground as possible.
- Snap or break pulled stems so they cannot root again on damp soil.
- Come back after 2–3 weeks for late plants.
Caution: Do not wait until the pods are ripe: at the slightest touch they fling the seeds metres away and you end up spreading it.
How it spreads
- Seed
- Each plant produces hundreds to thousands of seeds, which the exploding pods fling up to several metres.
- Along water
- Seeds float and are carried far by the current; that is why it grows mainly along streams and rivers.
- Stems and soil
- Broken stems can root again on damp soil, and seeds travel with moved soil, footwear and mowing machines.
Himalayan balsam: how does it get through the winter?
Hardy to 0 °C: protect in harsh winters.
- Annual: the plant dies at the first frost and disappears completely.
- Only the seeds overwinter in the soil; they germinate en masse in March–April.
- On banks it dominated, bare soil is left in winter that washes away easily.
Diseases and pests
- Dense stands: They crowd out native plants. Pull them up every year before flowering until the seed reserve in the soil runs out.
- New arrivals: Seeds wash in from banks upstream. Work together with neighbours and report large stands to your local council.
- Regrowth after mowing: Stems cut too high regrow from the nodes. Mow below the lowest node.
- Bare banks: After removal the soil lies bare. Sow or plant native bankside plants against erosion and new germination.
Through the year
- March: Mass germination along the water’s edge.
- April: Spot the seedlings; they are still small.
- May: Pull up young plants; they come out very easily now.
- June: Pull up before flowering. Start upstream.
- July: First flowers. Pull up or mow low before pods ripen.
- August: Look for missed plants. Remove plants with pods in a sealed bag.
- September: Late flowering. Check again.
- October: First frost: the plants die. Note the spots for next year.
You and this species
Did you know?
- Impatiens means ‘impatient’: the ripe seed pods burst open at the slightest touch.
- In English it is also called policeman’s helmet, after the shape of the flower, which resembles a British police helmet.
- It is one of the largest annual plants in Europe: in a single season it grows from a seed into a plant of 2 m or more.