Dictamnus albus - Fraxinelle, Buisson ardent, Dictame blanc, Dictame des boutiques, Fraxinelle blanche, Petit Frêne

Dictamnus albus, the dittany, is an uncommon aromatic perennial that forms a large, very floriferous clump in late spring. Its sturdy stems bear long clusters of pale pink flowers veined with purple. In hot weather, its foliage releases an aromatic oil with a lemony, resinous scent. Slow to establish, this plant then lives for many years with little care. Once well rooted, it tolerates dry summers remarkably well. It fits perfectly into herbaceous borders as well as dry gardens on stony, chalky soils.

This species belongs to the Rutaceae family, the same as citrus trees. It is a herbaceous perennial with a woody base: its leafy stems die back in autumn and regrow from the stump in spring. Its natural distribution range includes southern, central and eastern Europe, then extends towards the Caucasus, western and central Asia, as far as south-western Siberia and the western Himalayas. This botanical species is present in some French regions. It grows in clearings, open woodland, dry grasslands and rocky terrain, with a preference for chalky soils. The name dittany refers to its compound leaves, which resemble those of the ash tree in miniature. The plant develops a deep, thick, fleshy root. This allows it to draw water from deep soil layers, but also explains why an established plant resents being moved or divided. In the first few years, growth remains modest and flowering may be slow to appear. Once established, the clump persists for many years and gradually becomes more floriferous. The foliage reaches 60 to 70 cm in height. The flowering stems, stiff and upright, rise to 80 or 100 cm; the clump spreads 50 to 60 cm across. This plant bears leaves divided into oval to lanceolate leaflets, slightly toothed, leathery and glossy. The flowers, 2.5 to 3 cm wide, are gathered in long terminal clusters. Each has five irregularly arranged petals, the lower petal curving downwards, as well as ten long arched stamens. The petals are most often very pale pink, almost white, traversed by purplish-pink veins. The colour can vary from white to light mauve. Flowering begins in May in warm regions and occurs mainly in June and July in cooler climates. It is followed by the formation of five-pointed capsules that open in a star shape at maturity. The leaves, flowers and fruits bear glands that release volatile oils with a lemony, resinous scent. On a very hot, still evening, these vapours can produce a brief flame; they do not ignite spontaneously. This peculiarity also explains its nickname of burning bush. Dittany also contains photosensitising substances: contact with the plant followed by exposure to sunlight can cause a skin reaction. Its hardiness reaches -20 °C and it shows little susceptibility to diseases or pests. In regions with very hot, dry summers, the foliage may yellow after flowering and die back earlier.

Dittany is planted in the middle of a sunny border or in a dry garden. It can be paired with the smoky purple clusters of Baptisia 'Purple Smoke', the purple spikes of Linaria purpurea and Perovskia 'Little Spire', which flowers lavender-blue in summer, and Nepeta 'Walker's Low' for the same reasons. All these plants have a similar size and enjoy sun as well as well-drained soil that dries out in summer. Plant dittany away from paths to avoid contact with its foliage.