An unwanted Alien

Last year we discovered a few plants of the alien Indian or Himalayan Balsam, Impatiens glandulifera, also known as Policeman’s helmet after the shape of the flowers, growing in one of the water courses and on the adjacent allotment. The origin of these plants is not known.

Himalayan balsam is listed under schedule 9 of the Wildlife Act. Himalayan Balsam is regarded as an invasive weed by the Environment Agency of the UK Government. It is legislated under The Wildlife and Natural Environment (Scotland) Act 2012 under section 14 of the Wildlife and Countryside Act 1981nd Countryside Act 1981. It is an offence to plant this species or to cause it to grow in the wild. It was introduced to the UK in 1839 and is now a naturalised plant found mainly on riverbanks.

As an occupier of land –

We must not plant in the wild, or cause to grow in the wild, listed plants which are either non-native, or invasive non-native. This can include moving contaminated soil or plant cuttings. If we do, we can be fined or sent to prison for up to 2 years.

We must not do any of the following with them:

grow, cultivate or permit to reproduce.

The invasive weed can tolerate low light levels and can ‘shade out’ other plants so that it will gradually kill them off due to a lack of light.

Whilst Himalayan Balsam is an annual plant, its high level of seed production and vigorous seed dispersal means that it is highly invasive. Each plant produces at least 500 seeds, which can be propelled up to 7 metres from the parent plant by seed pods that are explosive to touch. Seeds remain viable in the soil for two to three years.

Hand pulling can be a very effective strategy where an infestation is relatively low. To attempt to fully eradicate Himalayan Balsam from a site, a key objective is to exhaust the plant’s seed bank. This is done by repeatedly removing adult plants before they set seed. Last year we managed to pull up and dispose of the plants before they set seed. So far, we have not recorded it again at the original location.

If you see this plant growing anywhere on the allotment, please pull it up and inform the committee of its presence. This should be done carefully to avoid stimulating the explosive release of any seed present. As a responsible Allotment Society, we have an obligation to control Himalayan Balsam populations on our land and help prevent the spread of the non-native invasive species. The photographs below by Bob Gomes illustrate the plant.