Colder weather serves as a reminder to winterize roses
It’s quiet right now on Rose Hill in Manito Park. The recent cold finished off any remaining rose blooms and darkened some of the leaves. The plants are resting and pulling nutrients into their roots, waiting for the garden staff to finish the winterization process.
Our climate makes hardening off and then protecting tender roses a must. The process started back in August when the plants got their last fertilization. The garden staff has kept the plants well watered since then so they don’t go into winter dry, especially since the long-range forecast is for a drier winter.
Now with the onset of colder November weather, the garden staff will start covering the plants with soil and mulch to protect them from the cold. They won’t have to protect all the plants, though.
The old garden, shrub and species roses need little if any winter protection. This includes the Gallica, Damask, Alba, Centifolia, Moss, China, Bourbon, Hybrid Perpetuals and a host of species roses. These plants grow on their own roots and can tolerate the cold. Even if they do die back, they easily regrow new shoots from their roots in the spring. All that needs to be done to get them ready for winter is shape them a bit by trimming back straggly growth and unruly branches.
Grafted tea, floribunda and grandiflora roses are a different story. The part of the rose with the pretty flowers is grafted onto a different rootstock to create a more vigorous plant overall. Unfortunately the tops are often not as hardy as the roots. As a result, the top can be killed by the cold while the rootstock survives and grows in the spring, often producing less-than-stellar flowers
Start the final winterization process in late October by cleaning up dead leaves around the plants and cultivating the soil. This kills or removes places where bugs and disease can hide, ready for next year.
Once we have had two or three good hard frosts (which we have had) and the nighttime temperatures are consistently below freezing, cut long canes back to about two to three feet. Remove any canes smaller than a pencil and any weak, dead or diseased canes. Leave at least five large canes evenly spaced around the plant. Any more pruning can be left until April.
Hill 10 to 12 inches of soil or compost brought in from another part of the garden around and over the graft point. The graft point is the swollen, rough-looking bulge on the lower stem. The compost you pile now can simply be spread out around the plants next spring. After the ground has frozen, top the soil mound with another foot of pine needles, straw or shredded leaves for more insulation. Pine needles and straw drain water away easily. Large, unshredded leaves from maples and chestnuts tend to pack down and not allow water through to the roots. In a dry winter this can be deadly for the plants.