Roses that Survive and Thrive in Colorado

After last November’s 77 degree cold plunge to 13 degrees below zero, most roses suffered die-back, some died to the ground and some died completely. But there were roses that had only minimal damage and some that will bounce back with a good show of vigorous growth and generous flowering this year. Here are some observations and conclusions about growing sustainable roses in Colorado.

         Roses are cane shrubs, similar to blackberries and raspberries. Their wood has a pithy center and is not as hard or as strong as a lilac. Consequently roses are more vulnerable to insects, diseases, desiccation and cold, but another consequence is that they can grow and regrow much faster than woody shrubs like lilac and viburnum.

         When a rose dies back by 10%-25%, that is not a big deal if the rose is a repeat-bloomer and blooms on new wood. If, as with wild roses and many heirloom roses, the rose blooms on the previous season’s growth, then a 25% die-back will result in fewer blooms. If that spring bloomer dies to the ground, then there will be no blooms that year.

         If your pink hybrid tea rose dies to the ground and the new canes bloom with red flowers, then it was grafted and the red flowers are from the root stock. This brings up the subject of own-root roses. “Own-root” roses are grown from cuttings, not grafted onto a rootstock. Therefore it is growing on its own root system. This approach produces a rose that is slower to grow the first year, but has several important advantages. Because the graft is the most cold-sensitive part of the plant, an own-root rose is generally more cold hardy. Also a grafted rose develops from a single grafted stem, whereas an own-root rose can send up dozens of new stems from its own root. So an own-root rose can renew itself, and can live much longer. It can also have many more flowers because there are more canes. And if an own-root rose dies to the ground in a bad winter, the rose that grows from the roots will be the rose you bought, not a root stock.

         These advantages are particularly important for less hardy (zones 5 & 6) but very desirable roses like the fragrant and beautiful David Austin English roses, and the uniquely colored Hot Cocao and Cinco de Mayo. A grafted specimen may cost $20-40, but will have to be replaced when it dies to the ground and regrows only the rootstock. Even some Hybrid Tea roses can be found on their own roots, which can help them survive cold winters.

         The own-root approach is also valuable for very hardy roses like the Canadian Shrub roses. Agriculture Canada has its own rose-breeding program to produce roses hardy enough for Canadian winters. Not only did their breeding develop roses hardy to zone 3 (minus 30-40), but they tested and found that the same hardy varieties withstood the winters and rugged conditions better when they were grown on their own roots.

         From our experience growing roses in the rugged and fairly dry conditions at Harlequin’s Gardens, the urban rose garden at the Boulder-Dushanbe Teahouse and at our home garden in Longmont, here are our observations:

Roses that suffered less than 25% die-back: CANADIAN SHRUB ROSES- John Cabot, John Davis, Henry Kelsey, Victorian Memory (aka Isabella Skinner), William Baffin, William Booth, Morden Blush, Morden Centennial, Morden Snowbeauty, Quadra, Emily Carr, Adelaide Hoodless

HEIRLOOM: Alba Suaveolens, Alba Semi-plena, Desiree Parmentier

SHRUB ROSES: Applejack, Lawrence Johnston, Fruhlingsgold, Persian Yellow       SPECIES: Rosa glauca, R. eglanteria, R. setigera

Roses that suffered 50% die-back, but are growing back very strongly:

CANADIAN SHRUB ROSES: Morden Sunrise, Hope For Humanity

HEIRLOOM: Louise Odier, Banshee, Sally Holmes, Baltimore Belle, Broadway Perpetual, Madame Hardy, Cardinal de Richelieu, Tuscany Superb

SHRUB ROSES: Seafoam, The Fawn, The Gift, Night Owl, Sleeping Beauty, Darlow’s Enigma (at Eve’s)

DAVID AUSTIN ROSES: Abraham Darby, Golden Celebration, Winchester Cathedral, Constance Spry

Roses that died to the ground or more than 75%, but are growing back strongly:

HEIRLOOM: William Lobb, Complicata, Rose de Rescht, Stanwell Perpetual

SHRUB ROSES: Iceberg, Darlow’s Enigma (at Harlequin’s), Lady Elsie May, Day Dream, Golden Wings

AUSTIN ROSES: Many own-root will bloom well this year

HYBRID TEAS: Pink Peace and many at Roosevelt Park in Longmont will be strong and bloom this year.

         A word about climbing roses: these are the most difficult roses to maintain without die-back in Colorado. In general, the most successful are the Canadian Climbers. Zone 5 climbers like Blaze can reach 15 feet long and be beautiful for a few years, then one cold winter results in a lot of dead canes that must be removed and a climber that looks like a shrub. And the highly acclaimed sport of Iceberg, Climbing Iceberg, is not successful as a climber here, even though the shrub form performs very well.

         Our recent November cold plunge was an extreme example of how even cold-hardy plants can be damaged by sudden cold, before they have had time to harden-off. Other factors that can affect the amount of die-back include: winter sun exposure, moisture in the ground and in the plant, wind, elevation, micro-climate, and general health and nutrition of the plant.

         The keys to growing sustainable roses in Colorado is to choose hardy varieties, choose own-root roses, feed them with an organic fertilizer (especially in September to store nutrients for the winter), support the soil life, water them at least once a week and before the ground freezes, and protect the less hardy ones with a loose mulch, a wind barrier and an anti-dessicant.