Coreopsis — A Top 10 Favorite

• By Pat Chadwick
• /
• July 2016-Vol.2 No.7
• /
• 5 Comments

If asked to name the top 10 perennials likely to be found blooming in my mid-summer ornamental garden, my list would include Coreopsis. Why? There’s something profoundly appealing and upbeat about seeing its masses of yellow blossoms scattered throughout the landscape.  Commonly known as tickseed (because the seeds vaguely resemble ticks), this native plant is one of the best-selling perennials in garden centers.  Its list of attributes is long:  in addition to being very attractive, it tolerates heat, humidity, drought, deer, rabbits, and shallow, rocky soil.  Bees and butterflies love its nectar.  Goldfinches and other small birds love its seeds.  It blooms profusely and has a longer bloom time than most perennials.   It makes a great addition to container gardens and is a long-lasting cut flower in floral arrangements.

There’s only one drawback to Coreopsis:  It tends to be short-lived and unreliably perennial.   Many gardeners complain that it dies out after just two or three years.  Other gardeners note that some selections self-seed all over the garden and pop up in unexpected places every spring.  Despite these issues, this old favorite continues to be well loved and is widely planted or replanted year after year.

Recognizing both the merits and drawbacks of Coreopsis, renowned plantsman Darryl Probst and others instituted a number of hybridization programs to improve the genus.  Results of plant trials, most notably a three-year trial conducted between 2012 and 2014 by the Mt. Cuba Center botanical garden in Delaware, confirm improvements made to the species through these hybridization efforts.

With so many extensively hybridized selections on the market to choose from these days, it helps to step back and gain a basic understanding of Coreopsis types and species.

TYPES OF COREOPSIS 

A member of the Asteraceae (aster or daisy) family, the Coreopsis genus consists of about 100 annual and perennial species.  They are either clump forming or rhizomatous.  Most Coreopsis species fall into the clump forming category.  Unfortunately, these tend to be short lived and some members of this group are best treated as annuals.  The rhizomatous species have greater longevity and are more reliably perennial.

A sampling of the clump forming and rhizomatous species of Coreopsis often found in garden centers throughout the Mid-Atlantic include:

• C. auriculata (Lobed or Mouse-Eared Coreopsis) – This rhizomatous species has orange-yellow blossoms and oval-shaped leaves.  It spreads rapidly by rhizomes as well as seeds and forms creeping clumps that are 2 to 3 feet tall when in bloom.  ‘Nana’, a dwarf cultivar, is half that size and considered one of the best of the genus.  Two popular C. auriculata cultivars, ‘Jethro Tull’ and ‘Zamphir’, have open-ended, fluted ray flowers.

• C. grandiflora (Large-flowered Coreopsis) –   This clump-forming species blooms early in the season and repeat blooms throughout the summer.  Although not reliably perennial, lasting only 2 or 3 years on average, it has a strong tendency to self-seed and may pop up throughout your gardens as a happy surprise.
  

  Coreopsis grandiflora ‘Baby Sun’

  Great for cottage-style gardens, it pairs well with Echinacea, Gaillardia, Liatris, and other “informal” perennials.  Some hybrid selections with C. grandiflora as one of the parents include ‘Early Sunrise’ (which is an All-America Selections Winner), ‘Sunray’, ‘Baby Sun’, and ‘Sundancer’.

• C. lanceolata (Lanceleaf Coreopsis) – This clump-forming species is very similar to C. grandiflora with its large 2-1/2” golden-yellow flowers, but it is a little shorter and has lance-shaped leaves that appear mostly just at the base of
  

  Coreopsis lanceolata

  the plant.  Although it doesn’t produce as many flowers as C. grandiflora, it is a longer lived species. It blooms in late spring, is more reliably perennial than some of its cousins, and is the most common Coreopsis species found growing wild along roadsides.  It readily self-seeds and can form sizable colonies.

• C. rosea (Pink Coreopsis) – This is the oddball of the Coreopsis family.  Whereas its cousins are predominately yellow and prefer average to dry soil, this species has pink flowers with yellow centers and prefers moist soil.  Also, it has a rhizomatous growth habit and is reliably perennial in clay-based soils.  Like its cousins, it is prone to powdery mildew but the disease is not so obvious on its narrow, ferny leaves.  Because of its pink coloration and reliability as a perennial, C .rosea is used extensively by hybridizers to broaden the Coreopsis color palette.

• C. tripteris (Tall Coreopsis) – Just as its common name suggests, this rhizomatous species is much taller than other members of the genus.  Ranging from 4 to 8 feet in height, it produces clear yellow flowers from mid-summer through early fall.  It tolerates dry soil but grows taller in moist soil.  This aggressive seed sower has a tendency to sprawl and is best used in a wildflower or prairie-style garden setting.

• C. verticillata (Threadleaf Coreopsis) —  Referred to in Armitage’s Garden Perennials as “the tough guy of the group,” this rhizomatous species, also called whorled tickseed, has very fine,
  

  Coreopsis verticillata ‘Zagreb’

  ferny-looking foliage and strong stems and sports profuse clusters of delicately hued flowers.  It typically grows in a dense, bushy 1 to 3 foot tall clump and is reliably perennial even in our clay soils.  Award-winning ‘Moonbeam’, ‘Crème Brulee’, and ‘Zagreb’ are included in the long list of cultivars with C. verticillata as a parent.

If you go into any garden center in pursuit of Coreopsis, you’ll likely be confronted with a huge array of hybridized plants that belong to series or sets.   A few of the series are described below.  Coincidentally, these four were all developed by master Coreopsis breeder Darryl Probst:

• ‘Big Bang’ Series — The ‘Big Bang’ series sets little, if any, seed. They put all of their energy into producing flowers.   Some of the plants belonging to this series grow to 24” or taller, including: ‘Cosmic Evolution’ (creamy white flowers suffused with magenta), ‘Cosmic Eye’ (deep red with golden yellow edges), ‘Mercury Rising’ (large single red flowers), and ‘Galaxy’ (semi-double yellow).

• 

  Coreopsis Li’l Bang ‘Daybreak’

  ‘Li’l Bang’ Series – This is a sub-series of the Big Bang series and expands the color palette with hues ranging from brilliant white to rosy pink. Members of this series bloom earlier than the Big Bang series.

• ‘Ka-Pow’ series – This series is similar in appearance to the Big Bang series but more compact (up to 20” tall). The large 2-1/2” flowers change colors with the seasons.  ‘Ivory’ (cream color flowers blush with magenta in cooler temperatures), ‘Lemon’ (yellow flowers blush red in fall), and ‘Cerise’ (burgundy flowers with paler edges).   All have good resistance to powdery mildew.

• ‘Leading Lady’ Series – This mildew-resistant series consists of three cultivars:  ‘Charlize’, ‘Sophia’, and ‘Lauren’.  The blossoms are sterile, which means the plants will bloom all summer on 10” to 12” stems and don’t need to be deadheaded.   All three bloom in a color that is more true yellow than the species.

In addition to the perennial form of Coreopsis, there’s an annual form, C. tinctoria, which is commonly known as plains coreopsis or golden tickseed.  This is a charming wildflower with yellow and red bicolor flowers.  Originally native to the Great Plains and the southern U.S., it has naturalized throughout much of the eastern U.S. and is frequently included in wild flower seed mixes.

Coreopsis tinctoria

Like its perennial cousins, the annual form of Coreopsis has also been hybridized to produce plants that are more compact, floriferous, and colorful than its wild parent.  Two particularly charming hybrids are ‘Salsa’, a compact 15” tall selection with yellow and red bicolor flowers, and ‘Jive’, a compact selection with bicolor blossoms that have dark red centers and white edges on the petals.

USES FOR COREOPSIS IN THE LANDSCAPE

Coreopsis is a versatile plant suited to beds and borders, cottage gardens, and naturalized areas.

• Scatter them throughout the ornamental garden for bright punctuations of color.
• Team them with the spikier shapes of Veronica, Liatris, and Salvia to add texture to your landscape.
• Pair the bright, cheerful yellow selections with contrasting blues or purples for a classic color combination.
• Combine with Echinacea (coneflower), Hemerocallis (daylily), Monarda (beebalm), Achillea (yarrow), and Gaillardia (blanket flower) in an informal meadow setting.
• Plant in masses or drifts for blocks of color.
• Use the airy threadleaf species to soften the appearance of bold-leaved plants.
• Combine the annual species with tall spiky accent plants and trailing “spillers” in a seasonal container garden.
• Plant in butterfly gardens to attract skippers, buckeyes, painted ladies and the occasional monarch.

CARE AND MAINTENANCE OF COREOPSIS

• Light:  Coreopsis prefers full sun (six or more hours of direct sun per day).   While it can thrive in part shade, it won’t flower as well.
• Water requirements:  Keep newly planted Coreopsis watered while it is getting established. Once established, it is drought tolerant although it will appreciate a drink of water during really hot, dry weather.  C. rosea is an exception, preferring consistently moist soil.
• Fertilizer:  Fertilizer is generally not required and, in fact, may cause the plant to look spindly.  If you fertilize at all, apply a light application of a balanced granular 10-10-10 formula in early spring.
• Soil Preparation:  Research indicates that a sandy, well-drained soil is ideal for Coreopsis. However, it will tolerate most soil conditions as long as the soil is well drained.  This is absolutely critical in winter when our heavy, clay-based Virginia soils retains moisture.  To solve the problem, add compost to flower beds to improve drainage and slightly mound the planting site so that the soil will drain faster.
• Deadheading:  Deadheading may not be your preferred way to spend your spare time, but the practice does promote more Coreopsis blooms well into the growing season.  It also helps prevent the plant from expending all its energy into setting seeds.  As you deadhead, remove both the spent flower and the flower stalk.  By cutting the stalks back to the foliage, you will have a much tidier looking plant.
• Shearing:   As flowering slows down in mid-summer, shear the plants by 25% to 50% to encourage re-blooming. Shearing will sacrifice some of the flowers and buds in addition to spent blooms, but the plant should be in full bloom again within a couple of weeks.
• Dividing:  To maintain vigor, divide every two or three years in spring or early fall. Water newly transplanted specimens regularly until they become established.
• Late Summer Care:  Coreopsis produces so many flowers that it simply wears itself out. To help prevent this, cut the plants back by half or more in late summer.  This may help improve its chances of surviving winter.
• End of Season Care:   The lazy gardener will be glad to know that it’s not necessary to cut Coreopsis back in the fall.  In fact, the stems help protect the crowns in the winter.  If, on the other hand, you like your garden nice and tidy, then cut the stems back part way, but leave 6 to 8 inches of stems in place. Clean dead leaves and other debris that can harbor pests away from the crown and apply a layer of compost around the plant.  A light layer of mulch applied in late fall around but not over the crown will help protect the roots from extremes in winter temperature.

PROPAGATION

Coreopsis may be propagated by seed, division and cuttings.

• Seed — Most species Coreopsis may be grown easily from seed, which germinates quickly and results in plants that are generally true to type.  Many of the hybrids are sterile and do not produce seed. Coreopsis selections with sterile flowers must be propagated vegetatively (either by division or by cuttings) in order to obtain plants that are true to type.
• Division — Divide plants in early spring before the foliage emerges.  This method works for both the straight species and for cultivars.
• Cuttings — C. grandiflora selections may be propagated vegetatively by stem cuttings.  They are easy to root, provided you can get enough of the plant material to do a stem cutting.

PESTS AND DISEASES

In ideal growing conditions (full sun and well-drained soil), Coreopsis is mostly trouble free.  Powdery mildew is its biggest problem, though it is often not serious enough to warrant treatment.  Consistently damp weather may cause a variety of problems for this plant, including slug or snail damage and fungal spots in addition to powdery mildew.  Poor drainage can cause crown and root rot.

SUMMARY

Accept the fact that, for the most part, Coreopsis tends to be a short-lived species.  This is particularly true of C. grandiflora.  However, many promising new hybrids have been developed with the goal of improving its reliability.  Also, changing the conditions under which we grow this plant can prolong its life and prepare it for winter survivability.  These include amending and slightly mounding soil to improve drainage, deadheading regularly, dividing the plant every two or three years, and leaving the foliage in place over winter to protect the crown from freezing temperatures.  In addition, keep in mind that rhizomatous species are generally better adapted to withstand extremes in soil moisture than clumping species.

SOURCES

Armitage’s Garden Perennials, Second Edition (Armitage, Allan M., 2011)

“Coreopsis for the Mid-Atlantic Region,” mtcubacenter.org/horticultural-research

Flora of Virginia (Weakley, Alan S., Ludwig, J. Christopher, Townsend, John F., 2012)

Herbaceous Perennial Plants, A Treatise on their Identification, Culture, and Garden Attributes, Third Edition, (Armitage, Allan M., 2008)

Lady Bird Johnson Wild Flower Center, The University of Texas at Austin, Native Plants Database, www.wildflower.org/plants

The Perennial Care Manual (Ondra, Nancy J., 2009)

The Well-Tended Perennial Garden (DiSabato-Aust, Tracy, 2006)

USDA Native Plants Database, plants.usda.gov