Lithodora diffusa Alba

The Lithodora diffusa 'Alba' is the white-flowered form of the diffuse gromwell, more commonly known to gardeners as the 'Heavenly Blue' or 'Cambridge Blue' varieties, with intense blue flowers. It is a small evergreen undershrub with a loose habit, forming a carpet of white stars in spring, creating a beautiful contrast with its small, very dark green leaves. It prefers acidic, well-drained, humus-rich, and rather dry soil, and is suitable for sunny borders, rockeries, at the base of conifers, along walls, or even in containers on the terrace.

The Lithodora diffusa (or prostata), formerly known as Lithospermum diffusum, from the boraginaceae family, is native to southern Europe (Pyrenees, Alps, Morocco), where it mostly grows in rocky areas of low mountains, clearings, and along the coast, on non-calcareous and well-drained soils. It is a creeping, prostrate plant with woody stems, not exceeding 15cm (6in) in height but spreading over more than a meter. Its growth is quite rapid once established. The hairy stems bear small linear and rough leaves, with a matte dark green color and prominent midrib, which persist on the plant during winter. Each leaf measures 0.5cm (0in) to 2cm (1in) in length and 0.5cm (0in) in width. The flowering period lasts for at least 2 months, between May and June, starting earlier in favorable climates and continuing until September if the soil remains moist. The flowers are small white blooms, 2cm (1in) in diameter, grouped in clusters of 3 to 4 units. The corolla, with a tube at the base, widens into 5 rounded lobes around a small hairy ring. This nectar-rich and bee-friendly flowering attracts pollinators. After pollination, the flowers produce small, hard seeds enclosed in the calyx.

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On a wall, in a rockery, among small bushes, at the base of a conifer hedge, on slopes, but always in acidic and light soil, this lovely pure white-flowered variety is an ideal companion for heathers, as it has almost the same cultivation requirements. The diffuse gromwell also pairs well with linarias, botanical tulips, or creeping wormwoods, preferably in partial shade or in sunny, poor, and well-drained soils.