Q: What is this shrub? It looks like the Cassia ‘John Ball’ I used to have in my garden, but this one produces masses of seed pods with lots of seed and seems to be becoming a weed around here.
Question from J. Mathieson, Onetangi
A: This looks like Senna septemtrionalis, which has the same common name, buttercup bush, as Cassia ‘John Ball’ whose correct botanical name is now Senna corymbosa ‘John Ball’. Both these plants can set seed and become weeds, though S. septemtrionalis seems to be spreading more in some areas, reaching 3-4m tall or even higher in some situations. In flower they are really quite attractive with large racemes of butter-yellow flowers, giving rise to the less commonly used name of ‘yellow shower’. Traditionally some sennas have been used as medicinal herbs in some countries and in modern medicine provide important ingredients in some laxatives.
While they provide a great splash of colour when in flower, you really should try to control their spread. You could chop the stem off at ground level and treat the freshly cut stump with Vigilant Gel or Cut’n’Paste Gel. Or at the very least cut off the old flower heads before it sets seed.
Answer by Andrw Maloy (The Plant Doctor)