Blue is a beautiful colour in the garden and I began to think of a herb garden filled with true blue in all its variations from ultramarine to cobalt to aqua. Blue blends perfectly with cool lemons, creams, ivory, sea gull greys and silver. Some lavender blue shadings could also be added. This cool colour combination would be very soothing to the eyes and very relaxing. If something livelier were wanted, perhaps a few strong sparks of clear yellow or softest apricot could be added to the palette.

The fragrance of herb gardens is so important as well as the intimacy they offer. Traditional inward looking herb gardens have always offered a retreat from the world. Whatever their design, a hedge or wall isolates the herb garden from the world. Herbal shrubs that respond well to clipping into formal hedges and fit the colour scheme include sweet myrtle Myrtus communis with spicily fragrant leaves and starry white flowers, sweet bay Laurus nobilis with spicy foliage used in cooking, and orange-blossom scented Pittosporum tobira with its glossy dark foliage and waxy cream flowers.

It is also tempting to create a more informal hedge. In larger gardens with a Mediterranean climate, olive trees can make a perfect, dense, grey-green foliaged hedge. Every breath of wind shivers the foliage into silver and sage. Other possibilities are the tea camellia Camellia sinensis with dark glossy foliage and creamy white flowers, lemon-scented tea-tree Leptospermum petersonii, the elderberry Sambucus niger, and the honey fragrant, heavenly blue Californian lilacs Ceanothus ‘Blue Pacific’, C. arboreus and C. thyrsiflorus. Leadwort Plumbago capensis smothers in sky blue flowers and forms a dense, drought and cold hardy, informal hedge. Philadelphus mexicanus with its intensely fragrant cream flowers would also be ideal. Perhaps the finest choice would be the magnificent double white, very fragrant, 2.0-3.0m tall shrub Rugosa rose ‘Blanc Double de Coubert’.

If support was available, the violet scented double white Lady Banks Rose Rosa banksiae banksiae, the primrose Yellow Banksia Rose R. banksiae lutea, and the treasured, milk white Shakespeare’s Musk Rose R. moschata (grown in herb gardens of the Elizabethan era) would all provide perfect backdrops. Or maybe the fruit-and-tea scented, softest apricot Noisette rose ‘Crepuscule’?

Some of the most beautiful of all blue flowered plants are cultivars of rosemary. ‘Tuscan Blue’ , very upright in habit to 1.5m, has long spikes of exquisite sky blue flowers. ‘Collingwood Ingram’ has a more relaxed form to 1.0m and the most richest heavenly blue flowers which smother the bush.‘Lockwood de Forrest’ is the perfect rosemary to create a rich blue curtain over retaining walls. The lovely, low-growing ‘Prostrate’ rosemary, and the Californian cultivar ‘Santa Barbara’ spill over paths and have clear sky blue flowers. The richly gold variegated, moderate sized ‘Genges Gold’ with blue flowers would also be ideal. For a cushionlike, upright sub-shrub, the blue flowered form of hyssop is a perfect choice with its intensely navy blue flowers and bitter mint foliage. Tough and old-fashioned Tweedia Oxypetalum has starlike flowers the blue of a Siamese cat’s eyes, and the sea hollies Eryngium spp. include some of the bluest flowered and foliaged of all plants.

There are many old-fashioned blue flowered perennial herbs. Monkshood Aconitum is available in exquisite blue cultivars with hooded flowers arranged densely along upright stems. Like foxgloves, monkshood is poisonous and should not be used in gardens where young children have access. Richly blue Delphinium elatum requires full sun in a wind protected position. Jacob’s Ladder Polemonium caeruleum was popular in medieval herb gardens. Its name comes from its compound leaves which were said to resemble the ladder that Jacob climbed to heaven. The ferny foliage forms a dense rosette from which emerges a posy of rich blue flowers. It likes moisture retentive soils and morning sun. The taller growing Spiked Speedwell Veronica spicata also has a number of rich blue forms and thrives in sunshine. A number of cultivars of flag iris Iris germanica are available in sky blue to navy. Columbine Aquilegia was once used as an astringent herb. The Alpine columbine A. alpina has exquisite, large, nodding, heavenly blue flowers. It needs limed soil and regular watering, as well as a fairly sunny position.

Several groundcover plants have beautiful blue flowers. Lungwort Pulmonaria was once used medicinally. According to the ancient Doctrine of Signatures the silver spotted leaves, which were fancied to resemble lungs, indicated its value in curing pulmonary diseases. Now a treasured spreading perennial for moist light shade, the nodding flowers are an exquisite blue, often aging to pink. Most violets are purple or lavender, but ‘John Raddenbury’, bred in the early 20th century in Australia, is sky blue as is the lovely ‘Baby Blue’ with its tiny-leafed shiny foliage. Bugle Ajuga is an excellent perennial groundcover herb for moist, fertile soils. It has glossy foliage and, in most forms, spikes of rich blue flowers. Periwinkles or sorcerer’s violets are another ancient herb, once used in love charms and philtres. It has astringent and tonic properties and is finding herbal use in the treatment of symptoms of diabetes The larger flowered Vinca major has masses of rich blue windmill flowers in spring and again in autumn. It makes the perfect groundcover for dry shade, easily controlled by whipper-snipping twice a year. A cream variegated leaf form adds light to dark corners, and the double flowered, heavenly blue V. minor is delightful in pots and hanging baskets.

Among the annual herbs with pure blue flowers are black cumin Nigella sativa, mentioned in the Old Testament and still used as a spice in the Middle East, and Love-in-a-mist L. damascena, particularly in its rich blue, double flowered form ‘Miss Jekyll’. They are treasured not only for for their exquisite blue flowers partly obscured by a mist of fine, threadlike leaves but also for their highly ornamental seedheads used in dried flower arrangements. Few flowers are as perfectly blue as those of borage Borago officinalis. The flowers were floated on punches and stirrup-cups for the Crusaders as they departed for war, as borage was believed to confer courage and dispel melancholy. The starry flowers were embroidered on many medieval tapestries, and on scarves carried by knights into battle. The young cucumber flavoured leaves are also used, finely chopped, in salads. Eccentric though it sounds, lie under a borage plant one day to appreciate the full beauty of its flowers! Forget-me-not Myosotis sylvatica is used in homeopathic medicine for respiratory ailments. In warmer areas, sow the seeds in autumn, in cold areas in spring to provide a carpet of fragrant blue flowers which will tolerate light shade. Salad and root cultivars of chicory allowed to go to seed bear tall stems of china blue daisy flowers before self sowing next spring’s crop.

The exquisite blues of this herb garden can be shaded with lavender blue. The fragrant chaste tree Vitex agnus-castus could be added to the mix used in the informal herbal hedges, and lavenders of various kinds placed in sunny, well drained positions, or in pots, with dolamite added to the soil. Other lavender flowered herbs include Cherry Pie Heliotropium with its delicious, intense vanilla fragrance in the forms ‘Vanilla Icecream’ and ‘Gold’, anise hyssop Agastache foeniculum with its dense spikes of butterfly attracting lavender flowers and anise scented foliage, and the large, wonderfully fragrant, lavender blue ’Bournemouth Gem’ sweet violet. For a lemon counterpoint, the cool coloured ‘Lemon Queen’ form of Milfoil yarrow Achillea millefolium would be perfect, and perhaps ‘Gold Flame’ honeysuckle trained upward on metal posts and grown as standards. For a touch of clear gold, the lacy blue foliaged perennial ‘Jackman’s’ rue with heads of yellow flowers is ideal for sunny positions as are yellow flowered evening primroses Oenothera spp., together with fennel, dill, and yellow pot marigolds Calendula officinalis. The latter two are annuals that can be planted in spring. The perennial lady’s mantle Alchemilla mollis with its pleated, blue-green, cupped leaves that hold raindrops and its cloudy heads of tiny yellow flowers would be an ideal inclusion for cooler gardens.

Ivory and cream selections might include creamy plumed, fern leafed meadowsweet Spiraea ulmaria for moist areas, and the fresh foliaged, cream and green variegated applemint ( also called pineapple mint ). White yarrow, the tall white musk mallow Malva moschata, pyrethrum daisies, and chamomile ( particularly the double Roman chamomile Chamaemelum nobilis var. flore-pleno) provide crisp white contrast notes for mid-summer, and the delicate white flowers of the orris root iris I. germanica ‘Florentina’ would be right for the spring garden. With heavy basaltic soil, I will indulge in a little fakery by growing Lilium longiflorum, but in sandy soils I would choose the glorious and equally fragrant Madonna lily L. candidum, beloved of monastic herb gardens. The silver and grey touches would come from artemisias like wormwood Artemisia absinthum, golden flowered cotton lavender Santolina chamaecyparissus, and from the two curry bushes, both with golden flowers and the strongest scent of roasting curry powder when touched, Helichrysum angustifolia and H. stoechas.