Diadem yarrow

Diadem yarrow is the marketing name for the compact, double-flowered Achillea ptarmica cultivar 'Versdidem', bred by Janus Verschoor. Its rounded clump carries snowy-white pompon flowers over fine-toothed green leaves from summer into early autumn, with another flush possible after light pruning. ## Characteristics The [U.S. plant patent](https://patents.google.com/patent/USPP33484P2/en) records the botanical classification as Achillea ptarmica and the cultivar denomination as 'Versdidem'; it was granted on September 14, 2021. The patent describes medium-green foliage, compact rounded growth, and a highly vigorous growth rate. It reports plants up to about 12 inches tall and 24 inches wide in landscape settings. The [RHS profile](https://www.rhs.org.uk/plants/541502/achillea-ptarmica-versdidem/details) gives broad maximum size ranges and describes narrow, dark-green foliage with fluffy double white flowerheads. The patent reports USDA zones 3–8. ## Garden use Use it in containers, borders, rock or alpine gardens, or as a low groundcover. [Concept Plants](https://conceptplants.com/varieties/achillea-ptarmica-diadem-versdidem/) recommends sun or partial shade and lists containers, flower borders, and groundcover; RHS favors partial shade and also lists rock gardens, pots, and cut flowers. The breeder representative notes that bees and butterflies visit its flowers. ## Growing conditions Provide well-drained soil. Concept Plants describes average soil, while RHS specifies moist but well-drained conditions and says this selection prefers more moisture than many Achillea. Reported mature sizes vary by source and growing conditions; allow room for a low clump to widen. ## Maintenance Lightly prune after flowering to encourage rebloom. Cut back untidy foliage in spring. RHS lists spring division as a propagation method; the patent documents true-to-type propagation by stem cuttings.