Photo: Blackstem Plants
Giant plants from the US prairies, Silphium are very robust perennials with tall stems bearing simple leaves, aromatic when bruised, and loose clusters of yellow, daisy-like flowers in summer and early autumn.
Cups form where the toothed leaves meet the thick stems, birds are said to drink from the water held in the cups hence the common name.
There are 15 species of Silphium but this one is particularly garden worthy with an RHS-AGM. However, a large garden is needed for these as each plant can grow 250cm high by 200cm wide. They are not invasive but set a lot of seed. Unwanted offspring should be pulled out when young before the deep tap root penetrates too far.
Grow in any moisture retentive soil in full sun.
Any, except boggy