Winter Container Gardening
Winter is an especially good season to explore the many pleasures of foliage in your garden planters – color, texture and lots of personality.
Planters must be chosen carefully for winter hardiness—clay, ceramic and terracotta planters are not recommended as they tend to crack following frost or freezing. Metal planters can retain the cold more than other materials. Resin, fiberglass, plastic and wood are good choices for a winter container garden.
Container Gardening through the Winter
- Since the planter raises the plant above ground there isn’t any soil blanket to insulate the roots of the plant. It is recommended that plants placed in containers be two zones lower in cold hardiness than the hardiness zone they are to be grown in.
- Slow-growing evergreens can be excellent choices for medium to large garden planters to provide greenery through the winter. Some examples are: Colorado Blue Spruce, Alberta Spruce, Weeping Norway Spruce, Umbrella Pine, Siberian Cypress, Arborvitae and Juniper.
- To help compensate for the moisture stress factor try ‘Soil Moist’…these granules absorb irrigation water and gradually release it as it is needed by the plant.
- Water only in winter when soil is unfrozen and approaching dryness. As winter sets in and the potting medium freezes, you must cease watering.
- In very wet regions, consider using ‘pot feet’ of either terra cotta or cast stone. They elevate the planter allowing it to dry out. This will eliminate or lessen the staining of surfaces by water draining from the planter and pooling at the base.
- The larger the planter, the greater insulation of the potting soil around the plants’ roots. This increases your chances of success and reduces stress on the plants’ roots.
- To extend your large planter display through to the spring, plant spring-flowering bulbs to the recommended depth before adding the other plants.
- Put trailing plants at the edge of the container, remember that plants grow more slowly in winter than summer, so pack them in fairly closely.
- During particularly cold or wet periods, move smaller planters close to buildings for added protection.
Many hardy perennials and ornamental grasses will survive just fine outdoors, or in an unheated space, as long as they are protected from severe cold. The issues facing plants that are left outside through the winter are:
- frost damaging leaves and tender shoots
- a hard freeze killing the entire plant
- freeze/thaw action of soil disturbing the roots or cracking the container
- the weight of snow or ice breaking the plant
Be sure to carefully consider each of these issues when deciding on how to over-winter your planters. The goal of overwintering most hardy perennials is to prevent them from getting too cold—not to keep them warm. A good winter temperature range for most plants is between 32-45F.
The most common approach for protecting plants outside is to wrap your pots with some kind of hay and burlap to insulate them. But if hay is too messy, there are lots of other things you can use: leaves, blankets, bubble wrap, or styrofoam packing peanuts. Any insulating material will work well.
To protect the top part of the plant from frost, place several tall stakes around the rim of the pot and wrap with plastic or cloth. Bubble-wrap is excellent for wrapping around your planters for insulation. If you can move your pots, take advantage of any heat or wind protection close to your house or other out-buildings. Grouping all of your garden planters in one place can make it easier to construct a protective shelter to protect them from strong winds or heavy snow.