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Not every plant needs a cover, and protection does not always address the same problem. Sometimes container roots need protection; elsewhere young bark needs guarding from rodents, or an evergreen crown needs shelter from wind and bright sun. Before buying material, identify exactly what risk you intend to address.
Consider age and location
An established plant in a sheltered courtyard and a fresh sapling on a windy plot face different conditions. Cultivar hardiness matters but does not describe every risk. Moisture, thaws, snow cover and root condition also affect the result.
List vulnerable plantings rather than provide identical covers for the entire garden. Note containers separately: their roots experience greater temperature fluctuations than roots in the ground. Choose a wintering location and protection suited to the crop.
Separate root protection from crown protection
Loose mulch can moderate conditions in the root zone but must not be piled indiscriminately against trunks and shoot bases. Use suitable bark guards with room for growth. They should prevent damage rather than cause it through rubbing or constriction.
A free-standing wind and sun screen may be more useful for young evergreens in exposed positions than tightly wrapped material. Main types of winter injury and protection are discussed by University of Minnesota Extension.
Retain airflow and access for inspection
For sensitive shrubs, use a frame and breathable covering appropriate to the crop. Material must not break branches or lie as a heavy wet layer on shoots. Do not seal a plant in plastic without ventilation.
Choose the final method and timing according to weather: insulation applied too early during warmth can create dampness and overheating. If uncertain, follow advice for the particular species and local conditions rather than one temperature threshold for the whole garden.
Check after weather changes
Inspect fittings after wind, loading after wet snow and moisture during thaws. Do not let a cover gradually become a wet shell lying on the shrub. Remove protection in stages in spring, allowing for returning cold and sun.
Photograph the result after winter. If a method repeatedly leads to damp-related damage or broken branches, reconsider it. Good protection fits a particular risk and leaves the plant alive and stable rather than merely hiding it until spring.