Himalayan balsam

By Julie Hollobone

 

Although an attractive plant with pretty flowers, this weed spreads quickly by seed and can cause problems by waterways

 

Many gardeners welcome the surprise of unfamiliar seedlings arriving in the garden  and Himalayan balsam (Impatiens glandulifera) is pretty enough to keep rather than weed out. Unfortunately, this plant has now naturalised after it was introduced to the UK over 150 years ago and is becoming a problem in gardens and alongside waterways .

 

Description

This weed is an annual, growing to about 1.8m (6ft) tall on stiff, hollow stems, encircled by pointed leaves.
 
The flowers appear in mid summer and are purplish pink, similar in shape to its cousin the busy Lizzie, but held on long stalks so that they form a slightly drooping flowerhead.
 
   
The green seedpods form quickly, then burst when ripe to shoot  the seed up to 7m (22ft) away.

The weed can be a problem as the numerous seedlings can clog shallow riverbanks, but as the plants mature, although architectural in stature, they can also shade out neighbouring plants.

 

Weed control

Try to stop the weeds seeding, so either pull out the plants when they are still young, or remove the flowerheads in summer before the seed pods swell. A large plant may start to form flower buds further down the stem so it’s best to cut the stem in half to be sure seeds won’t spread.

You could use a glyphosate based weedkiller if the weeds are growing densely over a large area, but there are restrictions on weedkiller use near water courses so this is only suitable for areas of waste ground or gardens away from running water.