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If your garden is in a cold area, we suggest that you bury the bud union by a couple of inches to give added protection during cold weather. If a spell of unusually cold weather is expected, or if your garden is in a colder microclimate, some winter protection is recommended. Protect the stems by covering them with about ten inches of partly-composted shredded bark or compost. In extremely harsh winters, a waterproof covering may be necessary.
Winter hardiness is affected by many different elements. These include:
Snow cover
Roses and other plants can withstand cold spells much more easily when they are insulated from the worst of the cold by a thick covering of snow.
Planting depths
When growing roses in colder areas, including zones 5 or below, we recommend that you plant the bud union at least two inches below the surface of the soil. A thick layer of mulch (around 10 inches of compost or partially composted, shredded bark) will give some protection if unusually cold weather is expected. Many gardeners also use a pile of conifer branches to provide extra protection.
Strong, cold winds
When the soil is frozen, very strong winds can cause the rose to become dehydrated. A great natural way to provide protection is to mound up the soil at the base of the plant and cover the rose with a thick layer of conifer branches. Alternatively, use a material such as burlap or hessian.
Spring and autumn temperature variations
Roses that are normally very winter hardy may experience problems when they are grown in microclimates where spells of extreme cold regularly alternate with spells of warmth. This can create challenging conditions for any type of plant which produces soft young growth.
Long warm spells in winter or early spring may trick the plant into thinking that the winter is over and it is time to start to grow again. When the next cold spell comes, the new, soft growth will be cut back by the frost. The frost can expand and split the soft stems, which may make the plant more susceptible to disease. Winter protection is very important in these areas once the young growth has started. If the growth is damaged, we suggest that the rose is given a final pruning after the last frost of the year.
Growing climbing roses in cold zones
Climbing roses grown in relatively sheltered positions against a warm wall will be significantly less exposed to the cold than roses grown on an arch in the middle of the garden. Extreme cold will tend to cut back the growth so it is always wise to protect at least the bottom stems with conifer branches or burlap sacking. Exposed climbers grown on an arch in zone four should be totally covered by tieing conifer branches around the arch.
Tree roses
The bud union or graft is the most tender place on a rose. In a tree rose, the three grafts are exposed to the worst of the cold. If you are gardening in a very cold area, extra protection can be provided by taking any or all of the following measures:
* Mound up the soil around the base of the tree rose.
* Prune the rose stems back.
* Bring the outer stems up and tie them loosely together using a loop of string.
* Place a sack upside down over the head of the tree rose and tie it firmly in place around the stem.
* Tie conifer branches or burlap sacking around the stem of the tree rose.
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