This perennial dies back to below ground level each year in autumn, then fresh new growth appears again in spring.

• Position: full sun or partial shade
• Soil: light, moderately fertile, humus-rich, moist but well-drained
• Rate of growth: average
• Flowering period: July to September
• Hardiness: fully hardy
  
  Dense and upright in habit, the grey-green foliage contrasts perfectly with the rose-tinted, purple flowers, which are attractive to butterflies and bees. Also, providing it gets plenty of sun (and it's dead-headed regularly) 'Schwellenburg' will continue to flower over a long period - offering lashings of late summer colour.
  
  
• Garden care: To prolong flowering remove the flower spikes as soon they start to fade. Cut back all the stems after they have finished flowering and apply a generous 5-7cm (2-3in) mulch of well-rotted garden compost or manure around the base of the plant in spring.