The process of winterizing ornamental shrubs is a preventative measure aimed at mitigating specific environmental stresses that can cause damage or death. Evergreens, in particular, remain metabolically active year-round, making them susceptible to moisture loss when the ground is frozen. Proper covering protects foliage from desiccation, which is commonly known as winter burn, and guards branches against physical breakage from heavy ice and snow loads. This preparation ensures plants retain their structural integrity and moisture balance, leading to a healthier start to the subsequent growing season.
Identifying Vulnerable Bushes and Timing
The shrubs most likely to require winter protection are broadleaf evergreens, such as rhododendrons, boxwoods, and holly, because their foliage continues to lose moisture through transpiration even when roots cannot absorb water from frozen soil. Newly planted shrubs, those at the edge of their cold hardiness zone, and those in exposed locations facing intense sun or wind are also highly susceptible to winter injury. Deciduous bushes, which drop their leaves and enter a deep dormancy, do not need covering for cold protection.
Preparation for winter should begin in late fall, allowing the plants to naturally harden off as temperatures drop. Covers should be installed after the ground has frozen solid or after several hard frosts, usually in late November or early December. Waiting until the plant is fully dormant prevents the development of fungal diseases that thrive in warm, moist, enclosed conditions. Applying covers too early can trap warmth and moisture, encouraging late-season growth easily damaged by cold.
Essential Pre-Winter Preparation
Deep watering should continue up until the soil freezes completely. This ensures the plant’s root ball is fully saturated, providing a reservoir of moisture for the foliage during the winter months. Since water loss occurs throughout winter, a well-hydrated plant is less likely to experience the damaging effects of desiccation.
Applying a fresh layer of organic mulch insulates the roots. A 2-to-4-inch layer of shredded bark or straw maintains a consistent soil temperature, minimizing freeze-thaw cycles that can heave shallow roots out of the ground. Leave a small ring of space around the base of the shrub, ensuring the mulch does not directly contact the stem, which prevents rot and discourages rodent nesting.
For upright or columnar shrubs, like certain arborvitae varieties, preparation is needed to prevent physical damage from heavy snow and ice. Use a soft material, such as cloth strips or canvas strapping, to loosely wrap the shrub in a spiral pattern from the bottom to the top. This gentle bundling holds the branches inward, preventing them from splaying and snapping under the weight of winter precipitation.
Choosing Materials and Covering Methods
The covering material must be breathable to allow for air circulation and moisture escape. Burlap is a widely used, durable, and inexpensive option that effectively blocks wind and sun while remaining porous. Horticultural fleece or polypropylene fabric is another choice, as it is lightweight and designed to insulate without compacting the foliage. Impermeable materials should be avoided as they trap moisture and cause damaging temperature fluctuations.
For sensitive plants, create a rigid, tent-like structure using wooden stakes or a wire cage placed around the shrub. Drive the stakes into the ground outside the branch spread, and drape the fabric over this frame. This technique ensures the material does not touch the foliage, preventing it from freezing to the leaves and allowing the shrub to breathe.
A windbreak shields low-lying shrubs or foundation plantings from drying air currents and sun exposure. Construct this by installing stakes and wrapping them with burlap or snow fencing on the side facing the prevailing winds. When covering a shrub completely, ensure the material extends to the ground to trap residual heat radiating from the soil. Secure the base with ties or weights so wind cannot lift the cover.
Guidelines for Spring Removal
Protective coverings must be removed promptly in the spring to prevent overheating and allow the plant to acclimate to increasing light levels. The time for removal is once the ground has fully thawed and the risk of a hard, late-season freeze has passed. Leaving covers on too long can cause premature budding, which is highly susceptible to injury from subsequent cold snaps.
Removal should be gradual to avoid shocking the foliage, which has been protected from direct sun and wind for months. Remove the coverings on an overcast or cloudy day, or in the late afternoon, to prevent immediate sun scald on the newly exposed leaves. Once the covers are off, remove any excess winter mulch piled near the plant crown to reduce the risk of crown rot as temperatures rise.