Avoid conditions and timing that would allow rodents to overwinter in the mulch. Grass clippings and leaves do not make good mulching materials. Straw or hay are excellent mulches. Mulch conserves moisture, reduces erosion and leaching, prevents rapid temperature fluctuations, and improves soil structure after it is incorporated. Don't forget spring removal.
Surround shrub containers with insulating mulch.
The amount of soil in containers is not sufficient to buffer the fluctuating extremes of winter weather. Other options would be to place the container into the ground or to store the plant in a sheltered location such as a crawl space or cool garage. Till and turn heavy or compacted soils, then add organics. This allows faster drainage and warming in the spring. More organic material may be added next spring when the soil is prepared for planting.