“Overwintering” plants usually means deadheading, dividing, pruning, mulching or bringing them indoors to protect them from the cold. Increasingly, though, varieties are being introduced that flower into winter and rebound in spring. They need no special care and deliver more blooms for the buck.
Two noteworthy examples are Ball Horticultural Co.’s Cool Wave petunias and pansies.
“These flowers have more hardiness because they were developed in many different locations, and strains were chosen from breeding stock that did best in temperature extremes,” said Cool Wave plant manager Claire Watson. “Not only are they resistant to cold but they also are more tolerant of heat.”
Some other flower varieties introduced recently to provide color over longer periods of time are bearded iris, daylilies, clematis and shrub roses. Many of those perennials bloom repeatedly through the growing season, unlike earlier editions.
Cool Wave’s extended flowering petunias have been on the market five years, quickly becoming consumer favorites. Pansies were introduced this year.
“They need less maintenance, have large-size flowers and their colors intensify with the cold,” Watson said. “They tolerate several light frosts and simply go dormant after a hard frost. They bloom even in the snow.”
Cool Wave series flowers can be mixed with traditional late-season plants like ornamental cabbage and peppers, kale, mums, lavender and millet. They return in spring to complement such early arriving bulb varieties as daffodils, tulips, hyacinth and crocuses. In short, they display well with others.
These are vigorous flowers, capable of spreading 24 to 30 inches. That makes them a vibrant groundcover. It also means that not as many plants are needed per pot or for filling bare spaces in borders or beds. Their extended bloom ability gives gardeners more versatility for flowerbed design. The new pansies and petunias provide three full seasons of bloom when grown in the South. Those planted in the Snowbelt are capable of surviving Zone 5 conditions (minus-10 to minus-20 degrees Fahrenheit) and will reappear soon after the snow melts.
“They can use a light layer of mulch as wintertime insurance but don’t really require it,” Watson said.
A great deal of breeding work has been done over the past several decades to insert the cold gene into different plant varieties, said Anthony Tesselaar, president and co-founder of Tesselaar Plants in Silvan, Australia.
“Winter gardening is the ultimate challenge in this kind of work,” Tesselaar said. “That’s what we all aspire to.”
Many plants are tested. Few, however, make the cut.
Hybridizers who do upwards of 200,000 plant crosses a year might be lucky to emerge after a couple of seasons with just one to 10 plants that look new or promising enough to bring to market, Tesselaar said.
“On average, anytime you get good genetics in plants it takes 18 to 25 years before you can get comfortable with them or predict their behavior,” Tesselaar said. “They don’t just pop out of the box.”