Name: Coreopsis

Common name: Tickseed

Hardiness: Zone 5

Mature height: 18 inches

Mature spread: 30 to 36 inches

Classification: Perennial

Landscape Use: Perennial and mixed borders and beds; en masse

Ornamental Characteristics: New and unusual colors for tickseed. Brilliant, apricot-orange, cherry-red, plum-purple, white or bi-colored blooms atop strong stems. Extended bloom period offers reliable color all season long.

Recently I had the privilege of visiting Darrell Probst’s Coreopsis test fields. The summertime display of the coreopsis fields is a sight that will be forever alive in my memory. More than 20,000 hybrids, in an astonishing diversity of flower colors and forms, were creating fireworks! It’s no wonder that the cultivars developed so far are referred to collectively as the “Big Bang Series.”

The test fields at a central Massachusetts farm where Darrell grows his seedlings represent over 10 years of hybridization efforts in hardy Coreopsis. These improved perennial forms are being evaluated for hardiness, extended flowering, distinctive flower forms, improved disease resistance, vigor and improved plant habit. The future of Coreopsis introductions looks as bright as the flowers themselves.

We always wanted to have a perennial plant that blooms like an annual – and now we actually do. To accomplish this, Darrell selected hybrids that have sterile flowers, which have few or no seeds. Sterile flowers will try to produce more flowers in order to set seed, which is wonderful for ornamental purposes as blooms continue from June through October. Another advantage of sterile flowers is that they’re not likely to reproduce, nor will they interbreed with other forms. You won’t find Darrell’s new hybrids sprouting up in other places in the garden where you don’t want them.

In the past you had a choice of one pink-flowering coreopsis (C. rosea) and several gold-flowering selections. But now the color range has extended to apricot-orange, cherry-red, plum-purple, white and many bi-colors. All of these colors will come in many shades from light pastels to some that are deeply saturated. There is now a Coreopsis for every color scheme.

The majority of coreopsis flowers form a single row of eight petals. Double flowers that resemble a double marigold will soon be available in many more colors besides gold. Even more unusual, there will soon be more flowers with fluted petals – petals that curl to form a tube or flute. There are even some novel forms that have cone-shaped petals that look like a cluster of megaphones.

Also new is an improved resistance to disease. Coreopsis verticillata is very prone to mildew. Several other coreopsis species can get leaf spot. By crossing and selecting the most disease-resistant forms, Darrell has developed new hybrids that are healthy and robust plants, making gardening easier and chemical sprays unnecessary.

An improvement of the plant’s form is a welcome change: Most wild forms of Coreopsis are about two feet tall and have a lax habit. They were best planted in groups or with grasses to help support them. Coreopsis verticillata always needed some pruning early in the season to develop a bushy form. Now we will have coreopsis that branch more easily, with stronger stems that won’t flop. Forget staking!

Out of 20,000 plants in Darrell’s test plot, 100 were picked to evaluate for possible introduction to the marketplace. Then out of 55 plants selected for possible introduction this year, only one has actually been released – a red-flowering coreopsis called ‘Mercury Rising’. Aptly named: This one’s going to be hot!

Courtesy of Steve Taylor

A truly hardy red coreopsis has been the Holy Grail of breeding for some time. The red color of ‘Mercury Rising’ comes from Coreopsis rosea, a perennial hardy through Nova Scotia, and not Coreopsis tinctoria. C. tinctoria is an annual and the parent of other red-colored varieties that are neither hardy in Zone 5 nor are long-lived perennials in warmer zones. Fortunately, ‘Mercury Rising’ is truly perennial. It’s been grown in central Massachusetts in Zone 5 for three years and has thrived in sub-zero temperatures. Slightly taller than C. rosea, ‘Mercury Rising’ grows 18 inches tall and spreads 30 to 36 inches wide. Like the rest in the Big Bang Series, it branches well, has excellent disease resistance and flowers from June through October. You won’t be disappointed!

Steve Taylor
Sunny Border Nurseries Inc.