The foxglove, Digitalis purpurea, is one of the most familiar of our wild flowers and certainly the most distinctive. Its association with man is long and complex.
Digitalin, which is extracted from it, is a powerful poison and an important drugs in the treatment of heart complaints. Yet the tall spires of long tubular bells and clear pink colouring made the step from medicinal hedgerow plant to border decoration inevitable.
Digitalis purpurea is a biennial, seeding freely when happy. Since it does not produce flowers (nor, therefore, seeds) until its second year, you must plant them two years running to have foxgloves every summer.
Seeds can lie dormant for years if conditions are unfavourable – if there is inadequate light or moisture. Occasionally, when an area of commercial woodland has been clear felled, especially when it is on an old site of deciduous trees, the next summer may yield a vast crop of foxgloves.
Whole hillsides become sheets of purple where the seed bank has been exposed and the sudden influx of light and rain enables it to germinate.
Although we associate it with woodland, the foxglove is essentially a hedgerow plant. It thrives best in dappled shade and is perfectly adapted to cope in sites where light varies throughout the day. It is an invaluable asset in a country where most gardens are small and separated from each other by hedges, fences or walls: perimeters are the most awkward areas of the garden but exactly the sort of venue this plant would choose for itself.
Typically, foxgloves are purpley pink and spotted within. Their colour varies subtly and colonies of pure white plants can occasionally be found in the wild. Gertrude Jekyll popularised Digitalis purpurea f. albiflora, which was an essential ingredient in her white planting schemes, and it has become one of the most popular garden plants.
Its immaculate flowers are tinged inside with green and, as with all wild forms, the bells hang from one side of the stem giving the plant grace and elegance.
Man has, of course, tried to improve on nature with the Excelsior hybrids, which produce blockbuster blooms with dense spikes of big bells all around the stems. But other varieties are much worthier garden plants and truly beautiful.
Digitalis purpurea ‘Sutton’s Apricot’ is subtle and graceful, and looks particularly well with bronze foliage. One of its greatest assets is the ability to mingle, a quality particularly important in contemporary gardens where the accent is on informality.
If you want a foxglove that will last more than two years, then Digitalis x mertonensis may fit the bill. A tetraploid species (having four chromosones instead of two) – in this case, the progeny of a mixed marriage between Digitalis purpurea and Digitalis grandiflora – it was raised in 1926 at the John Innes Horticultural Institution in Surrey.
The flowers are the colour of strawberry sorbet made from fresh berries and each bell is slightly squashed and broadened, an inheritance from Digitalis grandiflora. The basal leaves are large with a slight sheen. And it breeds true from seed.
Digitalis grandiflora or D. ambigua has been cultivated here for centuries. Widely distributed from Western Europe to Russia, and naturalised in Kashmir, it forms good rosettes of broad leaves from which rise several stems of creamy-yellow trumpet flowers. It grows in open woodland but is happy in our gardens tucked in the light shade between deciduous shrubs.
Some foxgloves from more southern climes, though originating in woodland conditions, are perfectly happy in full sun in our cooler climate. Their bold architectural spires make a superb vertical contrast to low growing Mediterranean shrubs and soft mounds of grasses. Digitalis ferruginea has small, rusty-brown flowers on long spikes. Digitalis ferruginea ‘Gigantea’ is taller still. Digitalis laevigata makes stiff spikes of tightly clustered, bronze flowers.
The foxglove is almost as striking an ornament when in seed, continuing to add its strong, thrusting uprights into the autumn.
Most foxgloves thrive in light shade. D. purpurea loves to be cool, but Mediterranean species need sun. Although foxgloves prefer lighter soils, they can survive on heavy clay with the addition of good compost to the top few inches of soil. The fibrous roots spread out vertically making vast mats to support the flower spikes, so mulch well to retain moisture.
If you are collecting your own seed, sow immediately when fresh – and thinly, as overcrowded seedlings are prone to fungal diseases. Pot up individually and grow on through the winter to plant out the following spring.
Digitalis ferruginea mixes perfectly with wafty Stipa tenuissima, Californian poppies and eryngiums for a dry sunny feel. Or use D. purpurea f. albiflora in combination with sweet rocket and Ammi majus. Digitalis purpurea is best with ferns and woodlanders.