Threadleaf coreopsis (also commonly called whorled coreopsis) is a rhizomatous perennial which typically grows in dense, bushy clumps to 1-3′ tall. ‘Zagreb’ is more compact (to 1.5′ tall) and features bright yellow, daisy-like flowers (1-2″ diameter) with untoothed rays and darker yellow center disks. Flowers appear singly in loose clusters (cymes) in a lengthy late spring to late summer bloom period which sometimes extends to first frost. Shearing plants in mid-summer (early August) when bloom usually tapers down will encourage a fall rebloom. Palmately 3-parted leaves with thread-like segments lend a fine-textured and airy appearance to the plant. Plants in the genus Coreopsis are sometimes commonly called tickseed in reference to the resemblance of the seeds to ticks.