Coreopsis or tickseed is a lovely flower, but it can be tricky to grow reliably for many of us. It is particularly frustrating when a variety doesn’t live up to expectations or dies out after just one season. To find out why, I dig into the backstory about why so many cultivars disappoint, and what to do about it.
I love the airy sprays of bright blooms on most coreopsis, but so many cultivars on the market today just don’t seem to last beyond a year or two. Blooming can be inconsistent and plants can die seemingly without warning. Yet I often see coreopsis gracefully thriving in other people’s gardens. Nurseries are full of them, so they are definitely popular despite sporadic performance. Why is that, and what am I missing here?
It turns out there are numerous reasons. Here’s what to know before you shell out for that captivating hybrid at the garden center this spring.
My Experience
I must admit, I was reluctant to plant tickseed at this house because I’ve had such volatile luck with it in the past. Moonbeam, the first commercially successful hybrid, did well for a while before finally dying out. Others I tried flowered unevenly, became diseased or disappeared after one season. So when I designed my gardens at this address, I deliberately left tickseed off the plan.
Recently I decided to take a chance and tried two new cultivars, one of which I put on my side bank. Not only did I forget to record the name, I forgot I planted it! Only by perusing last year’s photos did I discover it. The caption says it bloomed very late, in October. That’s a clue as to what it likely is — probably C. tripteris Gold Standard, a taller rhizomatous variety known for hardiness and disease resistance. I hope it comes back this spring so I comfirm identification.
The other one is Coreopsis rosea, a shorter native species with apricot-pink flowers. I put two on my sunny berm in well-draining loam. They overwintered and flowered nearly continuously last summer. The color works nicely with my existing plantings, and it does a great job hiding leggy roses. It is a bit floppy but easily staked, certainly not a reason to reject it. I like it a lot and plan to get more to better fill out the space.
That is the extent of my experience with tickseed so I did some research.
Confusing Cultivars
Because so many coreopsis are yellow-flowering it’s tempting to assume they bloom at roughly the same time and grow into similarly-sized plants. But that’s not the case. There are markedly different habits and traits among the cultivars but those traits often aren’t apparent on young nursery plants, and many buyers are unaware.
Part of the solution is knowing there are differences and paying attention to what you’re buying. But how?
To help sort out the confusion I turned to a trusted source, the Mt. Cuba Center in Delaware. Mt. Cuba’s mission is to promote native plants and and educate the public on the best cultivars and how they perform under typical growing conditions.
Mt. Cuba Coreopsis Trials
Luckily Mt. Cuba ran an excellent coreopsis garden trial a decade ago involving 13 species and over 50 cultivars. If you have even the slightest interest in growing tickseed, I strongly urge you to view their Coreopsis Trial Summary. Helpful photos and a wealth of information is presented in an easy-to-read format. (Expand the PDF to fill your screen; it’s best viewed on a computer, not a phone or tablet.)
For everyone else, I’ll provide the highlights here.
Top Trial Performers
Let’s start with hardiness, the most important factor.
In general, tickseed hardiness is most influenced by good drainage rather than temperature. The better the drainage, the more likely a given plant will survive the winter regardless of the cold.
There are two forms of perennial tickseeds: rhizomatous and clump-forming. (Hybrids have characteristics of either or both.) The best choices for hardiness in zone 6 are the rhizomatous varieties, with the top three being C. integrifolia, C. palustris and C. tripteris. They are all late-flowering starting in August and continuing into fall. Any cultivar or hybrid of these three is more likely to survive our wet winters.
BEST OVERALL: The top trial performer was a C. palustris cultivar called Summer Sunshine. It has robust bushy foliage with excellent disease resistance and longevity. The abundant and substantial flower coverage is natural looking and long lasting. Its bloom period is late summer into fall. A true winner!
Runners Up
Other top hardy choices include C. latifolia, C. major, C. rosea and C. verticillata. These varieties are all summer flowering starting in June or July. (Rosea is the only pink; the rest are yellow.) They do have a slight susceptibility to disease and may flop somewhat, but are worth trying.
Top performing cultivars in this group include C. tripteris Gold Standard; C. tripteris Flower Tower; C. integrifolia Last Dance; C. verticillata, verticillata Zagreb; and verticillata Golden Gain. All have yellow flowers. While they may look may alike when small they have significantly different mature forms.
No doubt you’ve seen Zagreb– it’s by far the most popular threadleaf tickseed on the market. Its habit is compact and rounded with very even flowering, like a big ball. At just 20 inches tall and wide, it’s also the perfect size for most gardens.
At 8 feet high, Flower Tower is too tall (in my opinion) for suburbia, and it needs other plants around it to hide its considerable stem bulk. But I love the charmingly informal Last Dance and Golden Gain, both of which stagger their flowers at randomly varying heights for a natural looking display. The straight species C. verticillata is also a possibility if you don’t mind its rather stiff-looking countenance.
Like a good roadmap, the trial summary clarifies key differences between the many cultivars trialed. It demonstrates that all coreopsis don’t behave the same, just because they sport similar-looking flowers or foliage.
Reliable Hybrids
In the trial, hybrids Gilded Lace, Center Stage, Full Moon, Moonbeam, Redshift, Route 66, Showstopper and Star Cluster all made the “reliable” cut. They are yellow except Showstopper, which is a brilliant magenta. Redshift is yellow with a dark red center and frilled petals.
Not recommended
The trial’s most unreliable were the clump-forming species C. grandifolia and C. lanceolata, or lanceleaf coreopsis. They are familiar species at garden centers and other plant outlets. They often have frilly or pleated petals in a richer shade of gold than the threadleafs.
If you consider either of these, know there is some risk. At least you’ve been forewarned if they end up being short-lived. My neighbor has a beautiful lanceolata clump that performs well year after year, clearly a case of “right plant, right place”. So success is possible.
By the way, lanceleaf tickseeds benefit from a light deadheading, unlike other tickseeds, extending their flowering period a bit. They are late spring to early summer flowering.
The Dreaded Unreliables
There are at least twenty lanceleaf cultivars and hybrids listed as “unreliable” by Mt. Cuba as a direct result of their trial; I’m not going to name them all here. They do include some commonly offered selections. Reasons vary from poor hardiness in clay to disease prone to weak growth. No wonder gardeners get frustrated.
The point is, some of these would likely do better in amended soil and drier conditions than zone 6 typically experiences. If you can provide well drained sandy loam, by all means try some of these if you wish. Unreliable doesn’t mean impossible! Just know that any failures may have more to do with the cultivar or the soil than your gardening care.
Annual Coreopsis
To muddle things further, there are also annual tickseed varieties on the market. Annuals expand the color range with dramatic bicolors, purples, even reds, and even some hybrids touted as perennial are bicolor. Sometimes it’s not at all obvious which ones are annual, resulting in disappointed gardeners who thought they were getting a perennial.
I’m not going to cover the best/ worst annuals and hybrids here but the Mt. Cuba Trial Summary does. (Of course the trial is 10 years old, and new hybrids have come out since then). Annuals are lovely in their own right; just know what you’re buying to avoid disappointment.
The Keys to Success
Let’s recap what we’ve learned.
- Provide good drainage. Aside from cultivar, according to Mt. Cuba, the best predictor of hardiness is excellent drainage and full sun exposure. Amend heavy clay with sand or loam no matter what you’re planting. Soggy conditions will kill tickseed faster than just about anything else.
- Keep a lookout for disease especially lethal downy mildew. This type of mildew exhibits sandpapery crystalline deposits on the undersides of the leaves, unlike powdery mildew which presents on the tops and is not gritty. If downy mildew is present, destroy the entire plant to stop the spread, as it will die anyway. Treat leaf spot or any other pest issues promptly.
- Don’t overwater tickseeds. Most prefer soil on the dry side with the exception of C. palustra Summer Sunshine and C. rosea, both of which can handle wet conditions and a wide range of soils including heavy clay. Drier conditions help reduce flopping too. If flowering declines, try dividing the plant about every three years.
- Know what you’re buying. Stick to proven, hardy cultivars if you’re worried about die-out. Ask or research its longevity, habit and bloom period. Buy from a reputable source, ideally one that offers a limited guarantee if the plant fails. Knowledge is power after all!
I hope this quick tutorial is helpful, and results in success for you. Don’t forget to check out Mt. Cuba’s trial results, whether for tickseeds or something else. Armed with luck and a little know-how, I’m confident you’ll find a choice that suits your fancy and survives to bring you a bounty of flowers.
