Threadleaf Coreopsis or Whorled Tickseed

(Asteraceae [also known as Compositae] - Daisy Family)

Form

• small herbaceous perennial
• maturing on average at 2' tall by 2' wide, but cultivars are often slightly more compact
• initially an upright clump growth habit, becoming radiating and rounded with age, then spreading by underground rhizomes to form a dense colony

Culture

• full sun to partial sun
• performs best in full sun in moist, well-drained soils of average fertility, but is tolerant of various urban stresses, including poor soils, dry soils, thin soils, soils of various pH, heat, and drought
• propagated primarily by crown division
• Daisy Family, with few disease or pest problems
• abundantly available in containers
• often needs division every third year for rejuvenation and to keep it in-bounds
• deadheading after the initial flowering period in mid-Summer will encourage rebloom later in the Summer or early Autumn

Foliage

• medium to dark green, opposite, and without petioles (leaves are sessile on the stems)
• fine-textured and extremely cutleaf, with the simple leaf deeply cut into linear segments, resembling at first glance a pinnately compound leaf or needle-like leaves in a whorled arrangement around the upright stems

Flowers

• shades of lime, yellow, and yellow-orange, depending upon cultivar; the disk and ray flowers are almost the same color
• flowering in July, then either continuously or sporadically for the remainder of the Summer

Fruits

• small fruiting heads, borne at the center of each flower, have many small seeds (supposedly resembling ticks, hence the common name), and are best sheared off after the flush of early Summer bloom, to promote sporadic rebloom later

Twigs

• not applicable

Trunk

• not applicable

ID Summary

• foliage is extremely cutleaf and sessile, appearing as needles in a whorled arrangement around the thin upright stems, while the flowers, profusely blooming in July and sporadically thereafter, range from lemon yellow to orange-yellow, very showy and enveloping the canopy of the upright or spreading perennial
• the shallow and spreading root system, exposed upon pulling back mulch or when dividing the rapidly growing crowns, is yellow in color

USAGE

Function

• beds, borders, mass plantings, entranceways, foundations, raised planters, and naturalized sunny areas

Texture

• ultra-fine texture
• thick density

Assets

• very showy and profuse yellow flowers in early- to mid-Summer, with the potential for sporadic rebloom if deadheaded
• fine-textured cutleaf foliage
• rapid establishment, with high ornamental appeal

Liabilities

• can easily get out-of-bounds within three years when in rich, loose soil due to its shallow, spreading underground stolons

Habitat

• zones 3 to 9
• native to the Southeastern United States

SELECTIONS

Alternates

• Summer-flowering perennials with warm colors (Coreopsis lanceolata, Crocosmia x crocosmiiflora, Helenium autumnale, Heliopsis helianthoides, Hemerocallis, Kniphofia, Rudbeckia nitida, etc.)

Variants

• Coreopsis rosea - formerly listed as Coreopsis verticillata 'Rosea', it has miniature light lavender-pink flowers with yellow centers, to 1' tall and 2' wide
• Coreopsis verticillata 'Golden Showers' - yellow-orange flowers, 2.5' tall by 2.5' wide, generally now replaced by the more compact 'Zagreb'
• Coreopsis verticillata 'Moonbeam' - a very popular cultivar and one of the very best perennials, having light lemon-colored flowers that prolifically rebloom after the intial mid-Summer flush, to 1.5' tall by 2' wide
• Coreopsis verticillata 'Zagreb' - yellow-orange flowers, 1.5' tall by 1.5' wide

NOTES

Translation

• Coreopsis translates as "resembing a bug", referring to the mature seeds that may resemble ticks.
• verticillata translates as "whorled", referring to the oppositely arranged, cutleaf, sessile foliage that appears as many needles in a whorled arrangement around the stems.

Purpose

• Threadleaf Coreopsis is an excellent perennial for profuse Summer flowering in sunny sites.

Summary

• Coreopsis verticillata is a popular perennial that has cutleaf foliage and a relatively long bloom period in Summer, with cultivars having showy flowers in various shades of yellow; it differs from Coreopsis lanceolata (also known as Coreopsis grandiflora) in that the latter has large lance-shaped foliage, slightly larger flowers that are in the gold and orange shades of yellow, and retains a clump-forming growth habit with age.