Outdoor plants face a significant challenge when seasonal temperatures drop, necessitating winterizing to ensure their survival. The primary threats are direct damage from freezing temperatures and desiccation caused by drying winter winds. Preparing plants for dormancy and protecting their root systems and above-ground structures are necessary steps for a healthy garden when spring arrives. This preparation involves timely actions designed to mitigate cold stress and moisture loss.
Preparing the Garden Bed Before Freezing Temperatures
Late fall is the optimal time to begin preparing the garden landscape, long before the ground completely freezes. A crucial initial step is garden hygiene, which involves removing all dead annual plants, spent vegetable stalks, and any diseased foliage. Disposing of this debris reduces the overwintering sites for pests and fungal spores, promoting a healthier environment for the following season.
Pruning should be minimal, focusing only on removing weak, damaged, or dead branches that are susceptible to breakage under the weight of snow or ice. Avoid heavy pruning, especially on spring-flowering shrubs, as this encourages a flush of tender new growth that will be instantly damaged by frost.
To encourage natural cold-hardiness, gardeners should cease applying high-nitrogen fertilizers by mid-to-late summer. Continued nitrogen feeding promotes soft, active growth, delaying the plant’s natural process of “hardening off” for dormancy. Proper hardening off involves physiological changes, such as thickening cell walls and increasing sugar content in tissues, which lowers the freezing point of the plant’s internal water.
Before the soil freezes solid, deep watering is one of the most effective preparatory measures, particularly for evergreens. Evergreens lose moisture through their leaves all winter, even when dormant. If their roots cannot access frozen soil water, the plant can suffer from desiccation, often referred to as “winter burn,” so they must be fully hydrated beforehand.
Protecting Permanent In-Ground Plantings
Established trees, shrubs, and perennials require insulation to protect their root systems from temperature fluctuations. Applying a thick layer of organic mulch helps to stabilize soil temperature, minimizing the damaging freeze-thaw cycles that can heave shallow-rooted plants out of the ground. This heaving exposes the roots to drying air and cold.
A mulch layer of about four to six inches is recommended, using materials like straw, shredded leaves, or wood chips. It is important to keep the mulch material pulled back a few inches from the plant’s crown or tree trunk to prevent moisture buildup and discourage rodents from gnawing on the bark. This technique ensures the insulation benefits the root zone without causing stem rot.
Tender shrubs and evergreens benefit from wind and sun protection, which guards against winter burn. Erecting a screen made of burlap or similar breathable fabric on the windward side effectively blocks harsh, drying air movement. For smaller specimens, temporary structures like tomato cages wrapped in burlap can create a protective enclosure.
Heavy, wet snow accumulation can cause structural damage by splitting branches, especially on upright evergreens. When snow load is substantial, gently removing it by lightly brushing the branches upward prevents breakage. A light, fluffy layer of snow, however, acts as an additional layer of natural insulation for dormant plants beneath.
Managing Container and Potted Plants
Container-grown plants are uniquely vulnerable because their roots lack the insulating mass of the surrounding earth, making them susceptible to rapid freezing and thawing. Tender plants, or those hardy only for warmer zones, should be moved to an unheated garage, shed, or cold frame to prevent root death.
If a container plant is left outdoors, insulating the pot itself is necessary to protect the root ball. Techniques include wrapping the container with thick materials like bubble wrap, burlap, or straw, which provide an insulating air layer. Grouping several pots tightly together against a protected structure, such as a south-facing wall, further creates a microclimate that buffers temperature extremes.
Even in dormancy, container plants require intermittent watering to prevent the root system from drying out. The soil should be checked periodically, and water applied sparingly when the top inch or two is dry, provided the temperature is above freezing. Overwatering must be avoided, as saturated soil can lead to root rot or cause the pot to crack if the excess water freezes and expands.
For pots made of porous materials like terra cotta, the freeze-thaw cycle poses a risk of cracking. These containers should be emptied and stored upside down in a dry location, or the plant can be transplanted into a more frost-proof material like fiberglass or wood. Placing containers up on pot feet or blocks also helps ensure proper drainage throughout the winter months.