Penstemon heterophyllus ‘Heavenly Blue’

This is a firm favourite in our perennial tunnels, and for good reason. From early summer and often right into autumn, it sends up spires of vivid blue flowers, each with a hint of pink or purple inside. The flowers are a magnet for bumblebees. It’s a semi-evergreen, so the narrow, blue-green leaves stick around for much of the year, forming a tidy, low mound.

It’s a compact plant, reaching about 50cm in height and spread. ‘Heavenly Blue’ is happiest in a sunny spot, though it can handle a little light shade. The most important thing is good drainage; it dislikes sitting in wet soil, especially over winter. It will grow well in most soil types, from sandy to loamy, as long as it doesn’t get waterlogged.

To keep the flowers coming, it’s a good idea to deadhead the spent spikes. In spring, once the worst of the frosts are over and you see new shoots at the base, you can cut back the old stems to about 15cm. It’s a great plant for cottage gardens, gravel gardens, or sunny borders.