Penstemons produce foxglove-like flowers, which look fantastic in informal and cottage garden schemes, and are extremely attractive to bumblebees. Penstemon ‘Sour Grapes’ is a robust, hybrid penstemon, bearing rich purple flowers from July to August. It’s ideal for growing in sunny borders, or in pots on the patio. Plants may need protection in particularly cold areas. Apply a thick mulch of well-rotted manure or compost in autumn to protect the roots.