Monday saw the entire garden team and many of our volunteer gardeners routing through the undergrowth amongst primed stinging nettles and lacerating brambles in the pursuit of Himalayan balsam (Impatiens glandulifera). It has many common names including Indian balsam, jumping jack, policeman's helmet, Indian touch-me-not, ornamental jewel-weed, pink peril and poor man's orchid. This invasive relative of the familiar tender busy Lizzie has become increasingly established along the boundaries of Harlow Carr particularly along the stream which transects the garden. It is a fast growing thug growing to two meters with broad leaves and a high tolerance of shade. It can quickly shade out our native flora and is common throughout Britain particularly along stream and river banks. It is swiftly dealt with by the first frosts but the damage is already done and the prolifically produced seed overwinters readily. The banks of watercourses regularly flood in the winter months but where the soil stabilising native plants have been smothered out the banks are susceptible to erosion. The flowers also produce large amounts of nectar and are popular with many native insects. This may seem like an arguably beneficial attribute but these pollinators are being drawn away from our sometimes less generous native wildflowers which are then unable to set seed.
Himalayan balsam was introduced into the UK in 1839 by one of our more famous botanic gardens where it was cultivated as a tender greenhouse plant before escaping into the wild. It has subsequently become naturalised throughout the British Isles and many other countries. In the UK it is classed as an invasive exotic by the Environment Agency who recommend cutting it down at ground level before the flowering stage in June/July. They warn that cutting down earlier can promote the formation of side shoots which can result in the production of even more seed. At Harlow Carr we weren't taking any chances and have pulled up the roots and all by hand. We expect we may need to repeat the exercise later on in the year and for several years to come before we can make a significant impact on the population size.
Preparing for 2009
This week we have been making plans for well into next year. Designs using biennials and perennials must be formulated and organised well in advance in order to get a flowering display for next year. This week we have been taking tip cuttings of hardy Salvias, Lysimachia clethroides, Nepeta and Aster novae-angliae ‘Andenken an Alma Potschke' in order to produce stock plants for bulking up next year. Self sown seedlings of the beautiful Digitalis x mertonensis, Gillenia trifoliata, Echinaceae and Angelica gigas have been potted up from our main borders for use elsewhere in the garden for next year.
The weather still remains mixed and we're still awaiting those long sunny days to encourage a few more flowers in the garden. The Russian Giant sunflowers next to Betty's Kiosk aren't complaing however and are currently reaching 3m tall with huge dinner plate sized flowers.
Andrew Chapman