Pond
Conservation
Sunday 10th September 2006
(We repeated
this again on Tuesday 19th June 2007 to try and get on top of it)
Himalayan
Balsam
Impatiens
glandulifera
Policeman's helmet, Indian
Touch-Me-Not, Ornamental Jewelweed
The Invader |
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Himalayan Balsam (Impatiens glandulifera) |
History
Himalayan Balsam (Impatiens
glandulifera) was first introduced in 1839 to Kew Gardens (in
the UK) from the Asian Himalayas as a greenhouse plant. It is an
attractive annual plant with pretty bright pink flowers and belongs to
the same family as the popular garden annual “Busy Lizzie”.
However unlike the Busy Lizzie it can grow 2 or 3 metres high. By 1855
Himalayan balsam had escaped into the wild and it is now widespread in
England and many other non-native countries where it has become
invasive. |
Conditions
It loves damp conditions
and colonises river banks and other damp areas such as marshland and
woodland. In the country park it can be found around the edges of the
seasonal pond. It grows in dense tall clumps and prevents light from
getting through to the shorter native plants trying to grow underneath
it. It can take over large areas if it is left unchecked. |

Mass of pink flowers around the pond as
we began. |
Invasive
nature
As well as depriving
native plants of light it also produces more nectar than any European
species of plant and therefore lures the pollinating insects, such as
bees, away from the native flowering plants. Scientists have measured
this by placing pots of Himalayan balsam in special experimental areas
where native plants were growing and then counting the number of bee
visits made to the native plants. Fewer visits by pollinating insects
means less pollination and less seed production, which is exactly what
was found to be occurring in the native species.
Large colonies of
Himalayan balsam, in river bank areas, increase the chances of erosion.
As an annual plant it dies back in winter exposing bare soil and with no
roots of native grasses to bind it together, the soil can then easily
get washed away.
A single plant can set
around 800 seeds. The seed pod bursts open at the slightest touch and
seeds can be propelled up to 7 metres away. The 2-3mm black, rounded
seeds float on water and in river bank habitats are carried downstream
thereby establishing colonies in new areas.
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Not a pink
flower in sight as we finished. |
Control
The
main aim in trying to control this plant is to prevent it from producing
seeds. This year in the country park this was done by pulling up the
plants before they flowered in June and then following up again in
September before the majority of them produced their explosive seed
pods. Next year it may be better to bring the second phase forward a
month or so, as we all witnessed first hand the seed pods exploding! The
plant has very small shallow roots and is easily pulled up by hand. Its
seeds cannot remain dormant for very long so if a site is intensively
managed it should be possible to dramatically reduce the population
within 2 or 3 years. |
Let’s see what
happens next summer! |
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