Hardy and borderline-hardy deciduous shrubs, small trees and vines
The stems, branches and trunks of these plants persist over winter, but the leaves drop off in the fall. Examples include miniature roses, rose standards, Japanese maples, clematis and dwarf lilacs. The goal is to keep plants dormant and within the range of winter temperatures they would tolerate if grown in the garden.
Use large containers and plants that are at least two zones hardier than recommended for your area. These woody plants have above-ground branches that hold next year’s flower and leaf buds, making them more vulnerable to winter winds than herbaceous perennials.
For the best protection, store them in an unheated garage, against the warmest wall. If practical, place them in a garbage bag loosely filled with dry leaves for even more insulation (leave the top open for air circulation). Keep in a dark part of the garage; light may trigger growth too early. Once a month, check soil to make sure it’s not bone-dry, but do not overwater, as this could cause plants to rot or break dormancy.
Hardy broadleafed and needle evergreens
These types of plants transpire (lose water) during winter, and when temperatures remain below freezing for long periods, root balls freeze solid and water is unavailable to the plant, causing leaf damage or possibly death. Examples include English holly, boxwoods, English ivy, cedars, junipers and yews. The goal is to keep them within their hardiness zone and prevent desiccation from winter winds.
Move pots to an area where they will be protected from strong winter sun and winds, and erect a burlap screen around them (don’t allow burlap to rest on foliage). Keep plants well watered until freeze-up and check frequently throughout the winter to make sure soil is moist. Thorough watering prior to freezing temperatures and again in March and April, when the root balls are most prone to thawing—and drying out—is crucial.
Tip: Don’t forget to assess the winter hardiness of your pots. Soil-filled containers exposed to long-term freezing may expand and crack. Those made of earthenware, ceramic and terracotta (unless designated as frost-resistant) are especially vulnerable; concrete, wood, plastic and metal are more durable, but the last two materials offer little insulation for plant roots.