Each spring drystone walls in gardens in the South West of the UK are covered in attractive daisy flowers belonging to a rather charming, if prolific, alpine plant with the tongue-twisting name of Erigeron karvinskianus. This Mexican native is such an opportunist species that it has colonised extensive areas of walls across the region, but will establish in the suitable cracks and crevices in other areas as well. The foliage of Erigeron karvinskianus is barely noticeable at the best of times, but when the plant is in full flower the clouds of pink and white daisy flowers are extremely attractive; the flowers start off pink and then go white when they mature.
Despite being an enthusiastic coloniser it can be tricky to get Erigeron karvinskianus established. Typically you find this plant sold in small pots on the alpine benches of garden centres and nurseries, but sometimes it’s just not possible to find a suitable hole to plant into. The best option is to plant out young plants at the base of a wall and allow them to seed themselves freely, but success relies on the suitability of the wall itself. Too clean and dry and the seedlings won’t germinate; the ideal wall is one that is old, possibly not carefully maintained, where years of crumbling mortar and plant debris have created perfect damp niches between the stones. Once seedlings have germinated they send thin roots deep into the wall in search of more nutrients and water, and this is where the traditional walls of the South West of England are perfect, providing the perfect balance between soil and rock.
If you don’t have the right wall for this charming little plant then you can establish it between paving or even in well drained borders, basically anywhere which is free draining and not too wet. You could get this species to naturalise amongst Aubretia, Saxifraga, Lewisia and other wall-dwelling alpines, but occasional editing of the Erigeron karvinskianus might be needed to prevent it swamping other plants (but this is easily done). Failing that, just allow the Erigeron karvinskianus to naturalise on its own; be warned though, once this charming little species gets established you’re usually stuck with it!
Erigeron karvinskianus is widely available in the UK.