Green roof plant of the week – Common Knapweed

Common Knapweed (Centaurea nigra) is a classic plant of rough grassland, dry meadows and road verges. This makes it ideal for planting on small scale large green roofs. It is also a great plant and is included in my species lists for brown roofs and biodiverse roofs.

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‘Hardheads’ as they are colloquially known have the appearance of delicate thistle yet without the spikes. The base of the follow has a black and green tartan appearance against the deep pink- purple flower heads.

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They flower between June and September and support a range of invertebrates,including butterflies, hoverflies, bumble bees and a day-flying moths. In fact it is one of the most attractive plants for a range of mini-beasts.

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Notable species that it is important for are the Gatekeeper, Large Skipper, Meadow brown, Painted Lady, Peacock, Admiral, Six-spotted and Four-spotted burnet moth and the Lime-specked pugmoth. Honey bees and various Bombus and Andrena species of bees feed its nectar.