A seasonal guide to the flora of the Welsh Harp

By William Griffin

Meadows, hedgerows, woodland, marsh, open water and even wasteland at the Welsh Harp all hold thriving plant communities. This seasonal guide covers the more attractive and interesting plants, including some spectacular wetland species that contribute to the Welsh Harp’s status as a Site of Special Scientific Interest (SSSI).


One of the first signs of spring is the appearance of silvery white buds on the Pussy Willow shrubs. These open into pollen-laden catkins, with the leaves forming much later. Crack Willows, which dominate the Northern and Eastern marshes, produce a verdant growth of leaves in April, their yellow male catkins appearing at the same time.

Perennial plants start to emerge along the hedgerows of the Northern shore. The bright green leaves of Dog’s Mercury begin to appear among the Ivy, and the arrow-shaped leaves of Lords and Ladies point upwards, their sheath of orange-red berries not visible for some months to come. On damper soils the flowers of the Lesser Celandine create a carpet of yellow. During May, when the Hawthorn and Blackthorn are in flower, the hedgerows become a mass of white blossom.


The warmth of summer produces rich growth in the marshes which fringe the reservoir. The Yellow Iris blooms along the water’s edge. Bulrush and the more delicate Lesser Bulrush will grow up to a height of two metres. These water-loving plants produce large brown seed heads. Flowering Rush, with its cluster of bright pink flowers, can often be found amongst them. Water Plantain, with its oval leaves and sprays of three-petalled white flowers, also thrives in aquatic conditions.

The sharp scent of the wetlands is that of Water Mint, a parent species of peppermint. A sweeter smell is produced by the cream-coloured flowers of Meadowsweet. Small colonies of the Common Spotted Orchid grow on both banks of the main reservoir and bright pink flower spikes can be seen among the Iris leaves. Gipsywort, with its white flowers arranged along the stem, grows in greater numbers.

Along the pathways low growing plants thrive in the light conditions. Red and White Clover, Daisies, Silverweed and Birdsfoot trefoil bloom throughout Summer.

The Dump — the large area of reclaimed tip by the Northern Marsh — now has an interesting plant community. Thistles and Teasels with their purple flowers are abundant. The small Yellow Snapdragon, also known as Common Toadflax, flowers until October. The notorious Hemlock, a tall relative of Cow Parsley, is easily distinguished by the purple spots on its stems. It is deadly poisonous. Towards the silt bund created by the dredging work lies an area of open grassland where, in a recent Summer, the attractive Bee Orchid appeared.

In the shade of the Easter Marsh, Himalayan Balsam is successful. The pink flowers have a sickly sweet aroma. The seed pods explode if you touch them, scattering the seed several metres. Deep in the marsh, Hop Vines climb the willow trunks. In open areas Rosebay Willowherb’s pink blooms provide attractive decoration. At the end of Summer a mass of white, fluffy seeds are produced.


As autumn arrives only the Michaelmas Daisy flowers with any vigour. Ash and Horse Chestnut trees soon lose their foliage and once the willows drop their leaves, the Welsh Harp begins to gain its bare, wintry appearance.

The Oaks keep their brown leaves until November. On windy days, fluffy seeds from Bulrushes and Thistles drift across the fields and the open water. Autumn is also the best season for seeing fungi. Shaggy Ink Caps, which drip black inky liquid out onto unsuspecting fingers, can be found on disturbed land while Puffballs, the white spherically shaped fungi, appear on lawns near the dam.


Many delicate plants will be beaten down by the first frosts. However, Thistles, Teasel and Burdock remain upright and dry out. Flocks of Goldfinches feed on their seeds throughout the winter. The orange-red berries on the Hawthorns and the Wild Roses provide winter food for Blackbirds and Thrushes.

In the cold marshes the Norfolk Reed stands high despite the ice and frosts. This is Britain’s tallest grass, standing well above head height. On damper nights hoar frost traces ice-crystals around the hardier plants, creating a beautiful visual effect. So even in the depths of winter, there is plant life to be enjoyed at the Welsh Harp.

See also:
Williams L.R. (2002) “Flora” in Birds of Brent Reservoir: The natural history of the Welsh Harp (eds L. Batten, R. Beddard, J. Colmans, A. Self). London: Welsh Harp Conservation Group.
Williams L.R. (2002) “Botanical surveying at Brent Resrvoir” in Birds of Brent Reservoir: The Natural History of the Welsh Harp (eds L. Batten, R. Beddard, J. Colmans, A. Self). London: Welsh Harp Conservation Group.
Williams L.R., Warren C., Hutchinson P.M. (1995). The flora of the Brent Reservoir, Middlesex. London Naturalist 74: 61-75.

© Welsh Harp Conservation Group 2019