2018: The Year of the Coreopsis

Every year, the National Garden Bureau, a non-profit organization promoting the pleasures of home gardening, selects one perennial, one annual, one bulb and one edible plant to celebrate. It’s a great way to discover a new plant or to learn a bit more about a plant you may already be growing.

Here’s the first of 2018’s four plants, the perennial called coreopsis or tickseed (Coreopsis). For information of two other 2018 winners, see 2018: Year of the Calibrachoa and 2018: Year of the Beet.

Origin

The genus Coreopsis is originally from the New World where it comprises some 80 species, about 45 of which are found in North America. They are herbaceous plants of generally modest size (rarely more than 2 ½ feet/75 cm tall), both annuals and perennials.

As is typical in the Asteraceae family (sunflower family), they bear daisylike inflorescences that look like individual flowers but are actual compound ones. They’re made up of a central disc of fertile florets surrounded by eight ray flowers (more in double and semi-double varieties), generally with a distinctly toothed tip. Yellow is the dominate flower color, sometimes with a reddish-brown halo.

The name Coreopsis is from the Greek “like a bug,” a fact that is reflected in the common name, tickseed. It comes from the bug-like appearance of the seeds of certain former species, beggar-ticks, which bear two projections that cling to fur and clothing like a tick. Oddly, beggar ticks were long ago moved to a different genus, Bidens. No current Coreopsis species have “bug-like” seeds!

Only a few species are cultivated, mostly among those that are the hardiest (the vast majority of species are tropical and can’t be grown, other than as annuals, in colder climates), but they still offer plenty of choices to fill out our flower beds. Many coreopsis remain in full flower most of the summer, especially if deadheaded. Coreopsis have long been popular in gardens because of their abundant and long-lasting bloom… they make excellent cut flowers as well.

Meadow Plants

In general, coreopsis are meadow plants, growing out in full sun. They’ll often tolerate partial shade, but still do best in a sunny spot. They adapt to well-drained soils of any type and most are quite drought-tolerant. However, good drainage, especially during the winter months, is vitally important to many species. Clay soils are especially problematic. You’ll find a lot of coreopsis do best in raised beds, as they ensure better drainage. Note too that coreopsis do prefer a soil that is not too rich, because overly fertile soil can lead to weak stems that tend to flop.

In general, deer avoid coreopsis, but pollinating insects (bees, butterflies, hoverflies, etc.) love them and seed-eating birds visit them in fall and winter… if you don’t deadhead, of course!

Spreaders and Clumpers

Perennial coreopsis have two distinct growth habits.

Rhizomatous varieties produce masses of single stems from creeping underground roots. They’re the most long-lived coreopsis, surviving for decades with little care and they’re the ones most tolerant of winter moisture. They’re not necessarily invasive, but may extend beyond their planting area if there are no plants shading them out and thus may be need to be controlled in certain situations.

Clump-forming varieties grow in tufts of multiple stems. They tend to be short-lived, especially in soils that remain moist in the winter, often only surviving only two or three years in the garden. You can, however, keep them growing for decades by starting new plants from divisions or cuttings every two years. As if to compensate for this short life, they are generally very easy to produce by seed, and many will bloom the first year from seed sown indoors, a feat not many perennials can accomplish.

Annual varieties, of course, always live just one year. Most maintain themselves by prolific self-sowing.

A Few Selected Species

Here are the most widely cultivated species:

Mouse-ear Tickseed or Mouse-ear Coreopsis (C. auriculata)

In a genus mostly composed of plants with narrow leaves, this coreopsis native to the southeastern United States surprises by its trifoliate leaves that are quite broad, sometimes even nearly rounded. The two small leaflets at the base of the much larger center leaflet are said to look like mouse ears, hence both the botanical (auriculata means “ear-shaped”) and common names.

The plant forms a low rosette of evergreen leaves and small yellow flowers. It’s a long-lived plant bearing short rhizomes, but is not really invasive. Being a short-day plant, it’s the earliest of the coreopsis to bloom, flowering from spring to early summer (most others are long-day plants, with mid- to late-summer flowers).

Dimensions: 12-24 in x 12 in (30-60 cm x 30 cm). USDA zone 3, AgCan zone 4.

The dwarf cultivar ‘Nana’, only 10 in (25 cm) tall, is the most popular mouse-ear coreopsis, but ‘Zamphir’, 12-24 in x 12 in (30-60 cm x 30 cm), with tubular ray flowers much like trumpets, is also widely grown.

Large-flowered Tickseed or Large-flowered Coreopsis (C. grandiflora)

This coreopsis was long the most cultivated species in the genus (C. verticillata now has that distinction) and most people simply call it coreopsis.

It’s a clump-former, producing a profusion of leafy stems with rather narrow leaves. The lower leaves are simple; those on the flower stems have 3 to 5 lobes. The inflorescences measure from 1 in to 2 in (2.5 cm to 6 cm) in diameter and are yellow orange, sometimes with a bit of reddish-brown at the base of the deeply toothed ray flowers. It blooms throughout the summer and into fall, especially if you deadhead (remove the faded flowers).

This species is one of the shorter-lived species, very intolerant of moist winter conditions and highly subject to powdery mildew. Keep it going through cuttings and division. Also, it multiplies quickly and easily by seed, blooming the first summer from seed started indoors in March.

In the wild, large-flowered coreopsis reaches up to 36 in (90 cm) in height, but almost all cultivated varieties are fairly compact, in the order of 16 in to 24 in (40 cm to 60 cm) in height. Both the species and cultivars form a clump about 12 in (30 cm) in diameter. It’s a very hardy plant, adapted to USDA and AgCan zone 3 and above.

There are many hybrids, including ‘Early Sunrise’ (double yellow, 16 in x 12 in/40 cm x 30 cm), easy to produce by seed and winner of both an All-America Selections Award and a Fleuroselect Gold Medal in 1989.

Hybrid Coreopsis (C. x hybrida)

These are a fairly new development, most having been launched in the 21^st century, but there are now over 100 cultivars and they are already widely sold in garden centers everywhere.

Most result from crosses between clump-forming species like C. grandiflora and C. lanceolata and rhizomatous species, like C. verticillata and C. rosea, although they often have narrow needle-like leaves of the latter. The color range is vastly improved: almost none are just plain golden yellow. Expect pinks, purples, reds, oranges, creamy white and all possible shades of yellow, with many bicolors, on flowers both single and double. Some have larger flowers that species coreopsis, but others have tiny, dainty flowers.

Winter hardiness is highly variable. Some are essentially subtropical and need to be used as annuals in the north. Most fall into the “limited” hardiness category: USDA zone 6/AgCan zone 7), but others are very hardy, zone 4 or even 3. Do check the hardiness zone on the label before buying to make sure the plant is suitable to your climate or you may regret your purchase. Even when you do plant them in the right hardiness zone, these hybrids are as subject to winter rot at C. grandiflora and will do best in well-drained soils or raised beds.

Although originally designed for flower bed use, hybrid coreopsis are also catching on as container plants, in which case they are usually treated as annuals.

Generally, hybrid coreopsis are fairly compact (18-24 in x 15-36 in/45-60 cm x 40-90 cm) and some are downright dwarf (6-8 in x 12 in /15-20 cm x 30 cm). Note that, unlike so many other coreopsis that are easily grown by seed, these hybrids are usually sterile or, failing that, are not true to type. They must therefore be propagated vegetatively (by cuttings or division).

Lanceleaf Coreopsis (C. lanceolata)

It’s one the most widely distributed species in the wild, from the Atlantic to the Pacific and from Ontario to Mexico. This plant is so similar to large-flowered coreopsis that the two are easily confused, but, as both common and botanical names suggest, it has narrower leaves. Even more distinctively, the large-flowered coreopsis has a leafy flower stems, whereas the upper half of the flower stalk of lanceleaf coreopsis is leafless. Also, it’s a longer-lived plant (4 to 5 years) than the large-flowered coreopsis.

Flowers can be entirely yellow, but most cultivars have flowers have a reddish-brown halo. Dimensions:12-24 in x 24 in (30-60 cm x 60 cm).

This plant sometimes self-sows excessively if you don’t deadhead and has escaped from culture to become a weed in Asia and Africa. USDA and AgCan zones: 3.

Swamp Tickseed or Swamp Coreopsis (C. palustris)

Not a well-known species, this disease-free rhizomatous plant has produced an award-winning cultivar, ‘Summer Sunshine’, that is attracting a lot of attention for its dense bloom and ease of care. ‘Summer Sunshine’ will do fine under most garden conditions, is very tolerant of partial shade and tolerates less-than-perfect drainage. Expect a plant 30 in (75 cm) tall and 40 in (1 m) wide with shiny dark green simple leaves and notch-tipped, brown-centered, golden-yellow flowers very late in the season: September through October. USDA zone 6, AgCan zone 7.

Pink Tickweed or Pink Coreopsis (C. rosea)

In a genus where yellow flowers dominate, the pink coreopsis certainly stands out, as its flowers really are pink. They are small, but produced in great quantities on thin stems over needle-like leaves. It differs from other commonly grown coreopsis in that it prefers soil that remains consistently moist at all times. Even so, it won’t tolerate either poorly drained clay soils or drought of any sort. It has the reputation of being a rather temperamental plant, behaving like an annual when the conditions aren’t quite to its liking. Where it’s happy, on the other hand, pink coreopsis will multiply slowly by creeping rhizomes. Do deadhead this one, not only for prolonged bloom, but to prevent self-sowing.

Dimension: 24 in x 24-36 in (60 cm x 60-90 cm). USDA zone 3b, AgCan zone 4b.

Pink coreopsis is widely used in hybridization and indeed, all the new pink, red, purple, etc. shades derive from it. Unfortunately, they also tend to inherit its short lifespan.

Plains Coreopsis, Garden Coreopsis or Calliopsis (C. tinctoria)

This is the most widely grown annual coreopsis. Easy to raise from seeds sown where they are to bloom, it is often used in flower meadows because it comes into flower so rapidly. Blossoms are usually bicolor (yellow and red), but there is a whole range of colors and flower forms.

This coreopsis self-sows readily. The epithet tinctoria means “used for making dye” and indeed, the Zuni Indians used to make a mahogany-red dye from its flowers. This was formerly a fairly tall plant (36 in/90 cm), but most modern strains are well under 24 in (60 cm) tall. Diameter: 12 in (30 cm).

Tall Tickseed or Tall Coreopsis (C. tripteris)

This is the giant of the genus, up to 8 feet (2.5 m) and also has particularly large flowers. Open masses of light-yellow flowers with a brown disc and uncut rays top the plant in late summer and well into fall, depending on your climate, making it one of the later bloomers in the genus as well. Both flowers and foliage give off an anise-like aroma. The stems are strongly upright and almost never need staking. The leaves bear three to (more rarely) five narrow leaflets. This is one of the rare coreopsis that can be invasive through its wandering rhizomes, but it’s also a no-nonsense, long-lived plant that needs next-to-no care. Plant it in an isolated spot where its invasive habit won’t be a problem and just let it do its thing. USDA and AgCan zone 3.

The species tends to be floppy, but selected cultivars are strongly upright and almost never need staking, plus they are denser-growing than the species and therefore not so invasive. Try C. tripteris ‘Gold Standard’ (7 feet/2 m) or C. tripteris ‘Flower Tower’ (8 feet/2.5 m).

Threadleaf Coreopsis (C. verticillata)

Its very finely cut, threadlike foliage makes the bright yellow, daisylike flowers almost seem to float on a fluffy cloud of green. This is a long-lived plant that blooms all summerwithout deadheading and some of its cultivars are very popular with gardeners.

It spreads by short rhizomes, usually without becoming invasive, and seems to adapt to most well-drained soils and from full sun to partial shade. This is certainly the best choice for novice gardeners, as success is nearly assured. It does have one flaw, though: it’s very slow to leaf out in the spring and that may lead you to think it has kicked the bucket. Instead, just trust it will be back and mark its location well so you don’t dig up the apparently empty space to plant something else. 36 in x 24 in (90 cm x 60 cm). USDA zone 3, AgCan zone 4.

This plant has given quite a few excellent cultivars, generally more compact than the species, including ‘Moonbeam’* (lemon-yellow flowers, 16-18 in x 16 in/40-45 cm x 40 cm) and ‘Zagreb’ (yellow flowers, 16-18 in x 16 in/40-45 cm x 40 cm), two classic varieties carried by almost every garden center.

*‘Moonbeam’, although sold as a selection of C. verticillata, is possibly a hybrid with C. rosea.

Be forewarned that hybrid coreopsis (C. x hybrida) with a similar habit to C. verticillata, notably needle-like leaves, are sometimes sold as if they were selections of C. verticillata. However, don’t be followed: they  have nothing near the stamina and the longevity of the species.

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If you’re fascinated by coreopsis, I highly recommend reading the report Coreopsis for the Mid-Atlantic Region by George Coombs of Mt. Cuba Center. Although the conditions the plants were tested under were extremely limited, the information may be of great help in better understanding the habits of these fascinating plants.

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Given the beauty, resilience, and popularity of Coreopsis, it is entirely fitting that the National Garden Bureau has designated 2018 as the Year of the Coreopsis.