The annual reproduction of the Himalayan balsam occurs in the summer, when the flowers are pollinated by insects. The insects may transfer pollen between flowers of conspecifics or from the same plant. The large amount of nectar produced by this species attracts a multitude of pollinators, including bees, wasps and moths. In an ideal environment, a single plant can produce up to 2,500 seeds, which are enclosed in capsules (3). Once mature, these capsules explode when touched (3) (5), throwing the seeds up to seven metres from the parent plant (2) (3) (5). The seeds are also distributed by animals and along water courses (3), although purposeful human dispersal is the main reason for the Himalayan balsam’s widespread distribution. A high proportion of seeds will be dormant throughout the winter, before germinating in spring (2). An abrupt seasonal temperature change usually determines when a seed breaks its dormancy and begins to germinate (3).
After germinating, the seedling has a period of rapid growth and begins to flower between July and October, although this is dependent on the amount of shade in the area (2). Flowering usually begins in July and may continue into October in certain areas (2) (3) (4) (6). Over winter, the mature Himalayan balsam plants decay, which gives the seedlings the chance to become established (3).