We will soon be heading into winter, with its potential for plant-damaging cold temperatures. Many homeowners have ornamental plants in above-ground containers. These plants may be more subject to cold injury, compared to the same species planted in the ground.

If you have plants like this, you may want to consider giving them a little extra protection this winter. The roots of plants in above-ground containers are obviously not as protected when the cold winds blow around your yard, compared to its siblings safely planted directly in the ground. The problem is even worse if the planter is on a deck, where the winds can sweep under the plant as well. To overcome these less-than-ideal conditions we have forced upon the plant, a little extra help is recommended.

To begin with, make sure that the plant is hardy enough to survive outdoors when planted normally. If it isn't, you will probably need to move it indoors or some place where the temperatures are modified.

For plants that are safe outdoors, make sure that the soil is moist before freezing weather arrives. You don't want the soil to dry out during the winter. This could be a problem if the plant is under the overhangs of your house, for example. If the moisture level is ok, then add a mulch to the planter. Several inches of shredded bark would be good. This not only slows winter drying, but adds some insulation as well. If you can somehow insulate the sides of the container, this will help. Home insulation or bales of straw will work.

There is one major precaution about mulch. It provides a great winter home for mice. If mice take up residence in your mulch, they may also want to chew on your plant, and may kill it in the process. A good example would be potted tree seedlings. If you use mulch around them, don’t put it right next to the trunk. Try to keep it away from the tree at least one foot. You might even consider burying the container in the soil, and limiting the use of mulch. The trick is to apply mulch around the container, and keep it away from the tree itself.

If you can move the planter, take it to a protected location, if possible. If the plant is not extremely hardy, a cold garage may be ideal, after the leaves fall off and the plant is dormant. This is especially true for small containers, where the roots are especially subject to cold temperature damage.

For planters that can't be moved easily, be sure to select plants that are hardy. Examples of plants with good winter durability include crab apples, juniper varieties, spirea, potentilla, dwarf cranberry, bush viburnum, and dwarf forsythia. Genetic dwarf fruit trees can be grown in containers, but be sure to protect them as much as possible to improve their survival. Some plants, such as tree roses, should be brought indoors to a cold room if they are growing in containers. The cold room is important for many plants that you choose to bring indoors, because they may have chilling requirements that have to be met in order to break dormancy. Chilling requirements are usually met at temperatures between 36 and 42 degrees.

It goes without saying that tropical plants will need special treatment. Many of them will not stand any chilling at all, and may be damaged at temperatures of 50 degrees and colder. Chilling injury is an interesting topic, since damage occurs well above freezing. But it won't be interesting for you if it happens to your tropical plant. I once had a call from someone in Southeast Missouri who wanted to dig up their rather tall banana and store it for the winter. This can be done, but it must be protected from cold and from drying out. The ideal site for tropical plants would be a sunny window or a greenhouse. If that is not available, do the best you can, keeping in mind the temperature and light requirements.

The containers themselves may have special requirements as well. Small containers made of plastic, clay, or metal are more susceptible to damage than wooden ones when they contain soil. The best use of these types of containers is to grow annuals, discarding the plant and soil before winter arrives. If you cannot store the containers indoors, place them so that water doesn't collect in them and break them by freezing. Leave the soil in wooden planters. If you remove the soil, it will allow the wood to dry out, which causes shrinkage and possible damage.