I have just been down the garden to see how things were doing and find that they are getting on. Not so many slugs and snails by a long way, and the new-planted things are growing now; the sweet peas promising well, the peonies in bud, as well as the scarlet poppies.’ We’ve all made similar reports, but this humdrum-seeming statement was the heart of a manifesto that revolutionised Britain’s houses and gardens.

The author is William Morris, designer and architectural conservationist, whose work is celebrated in Devon this summer. He is writing about the garden he created at Kelmscott House, Hammersmith, between 1875 and his death, aged 62, in 1896.

Morris’s passion for plants began in Epping Forest, where he botanised in boyhood. Churches soon joined wildflowers as the objects of his quests. He immersed himself in medieval English poetry, The Arabian Nights and old herbals. By the time he went up to Oxford, he had absorbed the elements of his art: close observation from life, the romance of the Middle Ages, monastic and Arabesque ornamentation, ecclesiastical carvings and woodblock floras.

He had also started gardening, and had decided what a garden should be. He dreamed of a hortus conclusus where roses and holly-hocks mingled with wildflowers ‘that had crept into the garden from without… all growing together in the glorious days of early autumn’. This fantasy became reality.

Begun in the early 1870s, his first major garden, at Kelmscott Manor in Oxfordshire, remains a shrine to him, maintained by the Society of Antiquaries (www.kelmscottmanor.org.uk). Both here and at Kelmscott House, hedges and wattle hurdles created chambers and bowers. For paving and walling, he chose vernacular materials used traditionally. Resembling tapestries and books of hours, the borders were treasuries of plants from times past violets and roses, pinks and columbines, bellflowers and forget-me-nots. Here and there, tiger lilies and acanthus would erupt, spectacular and statuesque.

The lawns recalled the medieval ‘flowery mede’, lush, spangled with fritillaries, ladies-smock and Tulipa sylvestris. Daisies were not only permitted, but petted: after all, Morris’s hero Chaucer had written in praise of them. Wildflower invasions were also welcomed-meadowsweet and water avens in Oxfordshire, willowherb and ox-eye daisies in Hammersmith. The only departure from this live-and-let-live philosophy was a dragon clipped in yew at Kelmscott Manor, inspired by the Icelandic sagas that were almost as important to Morris as the English Middle Ages.

All this was happening at a time when the garden of an educated Englishman with a private income and a thriving business was expected to be a showcase for flamboyant hybrids and fashionable exotics. Morris’s emphasis on native tradition and natural simplicity was shockingly avant-garde. It influenced the gardens of William Robinson and Gertrude Jekyll in much the same way that his design work shaped the Arts-and-Crafts house.

The printed form of his message was more successful than any verbal manifesto. It reached millions, reaches them still. He surrounded and seduced his audience with the fabric and wallpaper designs he made from the 1860s onwards. These two-dimensional gardens were directly inspired by his own. Just as he’d hoped, plants that were scorned or half-forgotten became celebrities via the names and motifs of his designs: Pimpernel, Blackthorn, Honeysuckle, Daffodil, Willow Bough.

Even in such teeming tableaux as Strawberry Thief (1883), where thrushes forage in a frenzy of violets, daisies, sunflowers, fritillaries, and pinks, Morris’s faithfulness to Nature remained paramount. All the plants were his, and all identifiable, however complex the pattern. Their raw materials were also homegrown at first, from the woodblocks on which they were carved to the vegetable dyes in which they were printed.

For a tangible celebration of Morris’s love of plants, it’s well worth visiting the RHS’s Garden at Rosemoor in Devon-its new exhibition, ‘William Morris:  Inspired by Nature’, opens later this week. No matter how familiar these designs have become, given our current preoccupation with indigenous plants and gardening in harmony with Nature, Morris’s vision seems more timely than ever-prophetic, in fact.

‘William Morris: Inspired by Nature’ at the RHS Garden, Rosemoor, Devon, runs July 3
-August 29 (01805 624067; www.rhs.org.uk/rosemoor)