Diamonds Blue Delphinium

Diamonds Blue is a compact, upright delphinium grown for vivid blue flowers and an unusually early display from seed. It can flower in its first year, making it useful for sunny borders, small gardens, and containers where a tall traditional delphinium would be out of scale. The breeder lists a mature height of 16–24 inches and spread of 10–12 inches, with hardiness zones 4a–9b. [PanAmerican Seed’s Diamonds Blue profile](https://www.panamseed.com/Products/022105576000616/delphinium-diamonds-blue/) gives the selection’s size, habit, color, and growing range. ## Growing conditions Choose a sunny site with fertile, well-drained soil. The species profile notes that this delphinium is often grown as an annual or short-lived perennial and flowers in early summer; local timing varies with climate and sowing date. Remove spent flower stems to tidy the planting and encourage continued care through the season. Blue flowers suit a cool-toned border and can be grouped with other sun-loving perennials. ## Maintenance Water during dry spells while plants establish, and avoid leaving roots in waterlogged soil. Deadhead after flowering and cut back tired stems. In colder areas, use the breeder’s zone range as a guide and provide good drainage through winter. [RHS species guidance](https://www.rhs.org.uk/plants/5399/delphinium-grandiflorum/details) describes the species’ sun and soil preferences and post-flowering care.