Protecting garden plants through the cold months ensures their health and vigor when spring arrives. While many perennials enter natural dormancy, their root systems and above-ground structures remain vulnerable to harsh conditions like intense cold, drying winds, and heavy precipitation. A proactive approach to winterizing minimizes preventable damage. Successful overwintering focuses on providing insulation and mitigating secondary effects, such as desiccation or structural breakage.
Essential Pre-Winter Preparation
Before the first hard frost, foundational tasks boost a plant’s natural resilience. Proper late-season hydration is important, especially for evergreens, which lose moisture throughout the winter. Watering deeply until the ground freezes ensures adequate water reserves to combat winter desiccation when soil water becomes unavailable. Hydrated soil also retains heat better than dry soil, providing insulation for the roots.
Applying a thick layer of organic mulch is another immediate protective measure for in-ground plants. A layer of shredded leaves, straw, or wood chips, typically 2 to 4 inches deep, insulates the soil and helps moderate temperature fluctuations. This shields the root crowns from repeated freeze-thaw cycles that can damage shallow roots. Spread the mulch around the plant’s base but keep it several inches away from the main stem or trunk to prevent moisture buildup and potential rot.
Pruning should be approached cautiously in the fall, as new growth stimulated by cutting live wood is easily damaged by frost. Focus on removing only dead, diseased, or broken branches that could snap off in a winter storm. Leaving the dead foliage on some herbaceous perennials provides insulation and protection for the crown. Major shaping or cutting back should be saved for late winter or early spring when the plant is fully dormant.
Protecting Stationary Outdoor Plants
For plants remaining in the ground, physical barriers defend against windburn and intense cold. Wrapping sensitive shrubs, especially broadleaf evergreens, with breathable material like burlap prevents winter burn. Burlap screens against drying winds and sun, which strip moisture from leaves when the ground is frozen. Creating an enclosure by staking burlap around the plant is more effective than direct wrapping, as it creates an insulating air pocket.
Building temporary windbreaks, such as a lattice or fencing covered with burlap, reduces moisture loss in exposed areas. For plants susceptible to structural damage from heavy snow loads, construct a protective cage. This involves driving stakes around the plant and securing chicken wire or hardware cloth to form a cylinder. These cages can be filled with loose insulating material, such as straw or chopped leaves, for thermal protection, especially for the graft union of roses.
Tying the branches of upright, multi-stemmed shrubs together with twine before a heavy snowfall helps them shed snow. This prevents the branches from splitting or breaking under the weight.
Strategies for Container and Potted Plants
Container plants lack the insulating mass of the surrounding earth, making their root systems highly susceptible to freezing. The most effective strategy for less hardy potted plants is moving them to a cool, sheltered location before the first hard freeze, such as an unheated garage or basement. These areas keep the temperature consistently cold but above freezing, allowing the plant to remain dormant. While indoors, drastically reduce watering to prevent root rot, providing only enough moisture to keep the soil from completely drying out.
For pots that must remain outdoors, insulation protects the roots from lethal temperatures. Grouping containers tightly against a sheltered wall creates a beneficial microclimate and increases their collective thermal mass. Insulate the pots further by wrapping the container walls with materials like bubble wrap or burlap, slowing heat loss from the root zone. Placing the pots on pot feet or bricks elevates the container off the cold ground and ensures drainage holes remain open.
Maintaining good drainage is important for outdoor containers, as standing water will freeze and damage the roots. The soil surface can be covered with a layer of mulch, such as shredded leaves or straw, to help retain soil warmth. Insulating the pot walls and covering the soil significantly reduces the rate at which the root ball freezes.
Addressing Specific Winter Hazards
Plants must contend with specific environmental hazards beyond simple freezing. Winter desiccation, or “winter burn,” occurs primarily in evergreens when leaves lose water but frozen ground prevents roots from replenishing moisture. This leads to the browning and drying of foliage. Deep watering and the use of windbreaks or burlap screens directly address this problem by reducing water loss.
Heavy snow and ice loads pose a physical threat, particularly to upright shrubs. While a blanket of snow provides some insulation, excessive accumulation causes structural damage by bending or breaking branches. Gently brush heavy, wet snow off branches using a broom in an upward motion, taking care not to pull down on the limbs. Ice should not be forcibly removed, as this almost always causes the branches to snap.
Frost heaving is a mechanical hazard that occurs when the repeated freezing and thawing of moist soil pushes shallow-rooted plants out of the ground. When the ground freezes, ice lenses form in the soil, expanding and lifting the plant. To prevent this, a thick layer of mulch applied in late fall keeps the soil temperature stable, minimizing freeze-thaw cycles. If a plant is pushed up, gently replant it and firm the soil around the roots before the next freeze.