‘A rose is a rose is a rose...’: Why is the flower so hard to grow?

Roses are notoriously difficult to grow but why is this and how can you make it easier, asks Margaret Roach

One way to succeed is to ‘feed the soil, not the plants’ (Getty Images/iStockphoto)

Roses have a reputation for being difficult to grow and disease-prone. But who’s really to blame?

We are, says Peter E Kukielski, a rosarian and the author of Rosa: The Story of the Rose, a new book about the flower’s place in human cultural history. After the genus Rosa had survived some 35 million years on the planet, it took us less than a century to render it less resilient than it had to have been to stick around that long.

“It has to be one tough plant to go through all the climate changes and everything else it’s gone through before we started hybridising roses,” Kukielski says, referring to the human interventions to change the flower’s shape into what became the hybrid tea, achieved at the expense of disease resistance.

So “give them some credit,” he says. And give them some proper companions, too: flowering perennials, annuals and bulbs that foster a healthier rose garden, without chemical intervention. Like the one he designed three years ago for the Royal Botanical Gardens in Ontario – a chemical-free province – that he proudly describes as “3,000 roses and 18,000 perennials chosen as insect-attracting companions.”

He adds: “I don’t mind bad insects. As long as we have the good insects, we will have balance.”

It’s no surprise that Kukielski doesn’t recommend a diet of synthetic fertiliser, or propping roses up with pesticides and fungicides if spider mites or black spot threaten. As a curator at the New York Botanical Garden, he won attention for his work from 2008 to 2014 on the Peggy Rockefeller Rose Garden – an approach that involved planting and trialing roses for disease resistance, using fewer chemicals. That served as research for his first book, Roses Without Chemicals: 150 Disease-Free Varieties That Will Change the Way You Grow Roses.

“When I first did the garden revamp,” he says, “choices of disease-resistant roses were kind of limited.”

But now there are many more roses bred with that intent, he says: “The rose world woke up to the idea that gardeners don’t want to rely on chemicals to grow their favourite flowers.”

Matching roses to regions

That pink rose on the latest catalog cover looks delicious, but wait: how would it fare where you garden, compared to similar-looking varieties?

“A rose is a rose is a rose … not,” Kukielski says. “Choosing the right one for your climate region can make for instant success. But the wrong rose will constantly be diminished, and the home gardener may give up.”

Breeding efforts focused on fragrance may not have the resistance, especially in hot, humid climates, against fungal diseases

Fortunately, he says, more companies are now educating customers about which regions a variety is best suited to: “It’s certainly an advance from where we were even five years ago.”

Breeders (on their wholesale websites) and retailers (on their consumer-focused ones) often make it possible to filter varieties by regional adaptability and disease resistance. So rose-shopping gardeners take note — and do your homework.

Some breeding has focused on cold-hardiness, producing varieties like the Buck roses from Griffith J Buck of Iowa State University or the Easy Elegance roses bred by Ping Lim. Other varieties meet the opposite challenge: The Sunbelt collection from Kordes Roses is selected for strong performance in warmer zones.

Certain trademarked series are marketed for toughness, including Carefree, Knock Out, Drift and Oso Easy, although there may be genetic trade-offs. As Kukielski pointed out, “When a series has been pushed to fill out an entire colour wheel of varieties, some colours – especially yellow – may be less resilient.”

Fragrance may also be diminished.

Yellow tends to be a less resilient colour (Getty/iStock)

“If you want a fragrant garden, depending on where you live there may be some disease issues,” Kukielski says. “Breeding efforts focused on fragrance may not have the resistance, especially in hot, humid climates, against fungal diseases.”

But putting scent back in is on some breeders’ to-do lists, he says. One example is the Parfuma collection from Kordes, a company long focused on disease resistance.

And the winner is…

There is no better proof of a plant’s durability than having data on what happens when it’s put to the test of multiyear garden trials in diverse regions. One programme currently underway is the American Rose Trials for Sustainability, which Kukielski co-founded, taking place at Longwood Gardens, the Scott Arboretum of Swarthmore College, Tucson Botanicals Gardens and university cooperative extension sites around the country, where roses are subjected to the challenge of no-spray environments, and offered no help from pesticides and fungicides.

Another is the American Garden Rose Selections Trials, with testing sites at Queens Botanical Garden, Chicago Botanic Garden and other places in diverse zones.

Both programs publish results and recommended varieties every year.

Some breeders are turning their attention back to fragrance (Getty/iStock)

For local information, try asking at garden centres with landscaping businesses, where employees may be able to recommend varieties that perform well for clients near you.

Or talk to the local rose society, Kukielski suggests, and neighbours who garden: “If the person down the street is growing Queen Elizabeth and it looks great, take that as a cue.”

Companion planting

Kukielski’s definition of a modern rose garden at any scale: “Not a monoculture, but a mixed border.”

Into his rose beds he layers a long season of companion plants, using a heavy hand, with emphasis on flower types preferred by beneficial insects (pollinators, predators and parasites alike). Grouping multiple plants of a single variety makes for a more inviting appearance than scattering one-offs around.

Of course, there are the classic rose companions: the chartreuse froth of lady’s mantle (Alchemilla mollis) or catmint (nepeta), with clematis scrambling up the shrubs. A range of allium – from tiny yellow-flowered A moly to towering purple Globemaster – and, later, self-sowing annual Verbena bonariensis (a butterfly favourite) make big statements.

But Kukielski also likes the umbel-shaped flowers of carrot family members, which are attractive to many beneficial insects — including, he hopes, tachinid flies, particularly one species imported in the 1920s as a biological control from Japan, where it is a natural enemy of the Japanese beetle that is a scourge to roses.

But the new hybrids are so resistant, I can put them closer. And as they grow together, the colours really show off – you’re painting with the colours

He is also partial to dill’s yellow umbels, its ferny texture and its inclination to sow around. And he allows coriander to flower and self-sow along garden edges.

Beyond dill and coriander, favourite herb companions include tansy, feverfew, lavender and thyme.

Composite, or daisylike, flowers have wide insect appeal, and Kukielski uses many, including asters, gloriosa daisy (Rudbeckia fulgida), coneflowers (echinacea), cosmos, sneezeweed (helenium) and yarrow (Achillea millefolium).

Native plants are, of course, particular magnets for insects: besides the asters, rudbeckia, helenium and coneflowers, Kukielski favors zizia aptera, wild bergamot (Monarda fistulosa), butterfly weed (Asclepias tuberosa) and cultivars of penstemon, Phlox paniculata and goldenrod (solidago), plus perennial grasses like prairie dropseed (Sporobolus heterolepis) and switch grass (Panicum virgatum).

Feed the soil, not the plants

Think healthy soil, not bagged fertiliser, Kukielski advised. “When I stopped feeding my roses and started feeding the soil,” he said, “the rose garden became a lot easier.”

He was inspired by the Earth-Kind methods promoted by Texas A&M AgriLife Extension. The inspiration for the soil-management practice, as he translates it: “Think forest floor, where nobody fertilises but leaves fall, that then break down and feed plants.”

Roses need plenty of companion plants to thrive (Getty/iStock)

To mimic that process, he puts down three inches of mulch, maybe an inch of which has decomposed into humus by season’s end, benefiting soil health and fertility.

“Just top up the mulch again next spring – but don’t disturb the soil,” he says. “Once we started doing that at NYBG you could just tell that the plants were happier. There was a big difference by year three.”

At his home garden, he also allows fallen tree leaves to remain in place and degrade. He hasn’t fertilised in three or four years, he says, beyond an occasional soil drench of dilute fish emulsion.

By using disease-resistant, regionally appropriate roses, Kukielski has also been able to break the rose-spacing rules established to minimise black spot.

“When I first started on the Peggy Rockefeller garden, I did get comments on that,” he recalls. “‘The plants should be six feet apart,’ people said. But the new hybrids are so resistant, I can put them closer. And as they grow together, the colours really show off – you’re painting with the colours.”

The next challenge: rose rosette disease

Today, rose researchers and breeders face a formidable opponent. Rose rosette disease, a naturally occurring virus, is spread by a tiny, windblown mite that has used the invasive multiflora rose as a host to expand into an increasing territory.

Early symptoms of infection include abnormal growth: excessive thorns, red pigmentation and general disfigurement – even what is known as witch’s broom, growth that resembles birds’ nests.

Industry and university experts have created a website about the disease and ongoing efforts to combat it. But at the moment, only vigilance – including eradicating nearby multiflora roses – and drastic measures are prescribed.

“If the gardener does discover it in the garden, the plant should be removed and destroyed, roots and all,” Kukielski says.

But a new rose can be planted right away, as the virus cannot live in the soil. Or you could just let all those companion plants take up the slack.

© The New York Times