Answer: Your rose bush will suffer much less shock if you time your transplanting to coincide with the regular dormant season of the plant. This will be December or January in your gardening region. Begin digging as far out as the canes and stems extend, and about 12" deep. It's better to dig too large a hole than to risk severing important roots. By rocking the plant gently back and forth after removing so soil, you'll be able to decide how much deeper you'll need to dig to get most of the roots out intact.
Be sure to prepare the new planting hole before digging the shrub, and transfer as quickly as possible so the roots are not exposed to the elements any longer than absolutely necessary. Water well after transplanting, to help settle the soil.
Roses in the Pacific Northwest do not generally need any winter protection. If this winter turns out to be unseasonably cold or snowy, you'll want to mulch over the roots and pile straw or pine boughs over the top 12" of canes, then postpone transplanting until late February, just before new buds begin to swell.
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