Giant hogweed is an impressive plant and can reach heights of up to 5-6 metres. It is therefore much taller and has altogether larger dimensions than any related native plant. The plant is not native to the UK, and was introduced from south-west Asia in 1893 as an ornamental plant. The hollow stems are green with reddish-purple blotches, and up to 100 mm across. The leaves are dark green and jagged, ending in a spike, and arranged in rosettes around the stem. The many small white flowers appear in June or July and form an umbrella-shaped head (umbel) up to 500 mm across. It can take up to four years for a Giant hogweed to flower, but each plant can produce 50 – 80,000 seeds
Giant hogweed grows well where the soil has been disturbed, such as wasteground, roadsides and riverbanks. Here they will shade out native vegetation. The seeds are easily dispersed by water, so it is often seen spreading along watercourses. It is widespread in Norfolk with ‘hot-spots’ to the south and east of Norwich. After flowering, the whole plant dies off. This can cause problems with soil erosion if large areas of riverbanks are left bare over the winter.
NOTE: Giant hogweed is a toxic plant and a public health hazard. The stems, edges and undersides of the leaves have small hairs which contain poisonous sap. The slightest touch causes the skin to become photo-sensitive, so that exposure to sunlight causes severe burns and blistering. For this reason, protective clothing must be worn when dealing with this species.