Cowslips (Primula veris) have clusters of yellow, nodding flowers, borne on tall stems. They can be seen on green roofs from mid march. In London, probably due to the Urban Heat Island, they have been seen to flower in early MarchA delightful plant they are quite robust and can grow on very harsh green roofs in terms of nutrients. On the Laban Dance Centre, which is essentially crushed concrete there is a small population. They first appeared in 2009 and are gradually spreading. They are generally found on well drained soils, making them ideal for green roofs.
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There is a wonderful green roof at the the Wildlflower Centre in Liverpool, which has a wonderful display of Cowslips from late March to mid May.
In the UK Cowslips declined in the last century due to changes in farming practice. Ensuring that they are included in planting specifications and designs for extensive green roofs for biodiveristy, whether they be brown roofs or biodiverse roofs is important in supporting there gradually comeback.
They are also a very important nectar and pollen plant for bees, butterflies and other invertebrates. This is especially important in early to late spring, when sources of food are relatively limited.
A wonderful addition to a green roof and one that will give a great deal of visual pleasure.
There are a number of green roofs in London where Cowslips grow including two roofs above St. James Tube Station and the Laban Dance Centre.