Native Plant of the Month : Brush Senna

Brush Senna brings sunshine into the garden with its summer-long display of bright yellow flowers.  It is occasionally mistaken for the weedy Cassia (Senna pendula var. glabrata), a South American plant which fell out of favour in gardens because of its tendency to grow too large, too fast, too leggy and too weedy-looking. Cassia is now sadly more common than the native Senna as it has jumped the fence to become an environmental weed. It may come up in your garden whether you want it or not.

The Brush Senna is easily distinguished from the weed Cassia by their flat black seed pods (Cassia has long round pods like green beans). Brush Senna has a longer flowering period. It grows to between waist and shoulder height subject to your pruning of the plant and makes a dense screen.  It will self-seed but is easy to grow from seed using the hot water method (soak in hot water, just off the boil, dry and plant).

The lifespan is somewhere between four and ten years. Plants that are pruned, fertilised and watered once a year after flowering (in autumn) live a long life. They are always aware of the sun, closing their leaves at dusk and reopening in the morning. Sennas are tough, drought hardy plants, tolerating all but the hardest of frosts.

Butterflies like to hang around their host plants – the plants which have the right kind of leaves to feed the young of their particular species – and sennas are hosts to a number of butterfly species. It is a great idea to put in a group of these pretty, sun loving plants, making it easy for butterflies to notice your garden and move in. Some of the butterfly visitors will be the small grass yellow, large grass yellow, lemon migrant and yellow migrant.