Any cold-hardy plant should be planted in the ground as soon as possible after purchase. That way, it has more time to establish roots before the ground starts to freeze. Air temperatures don't have much bearing on planting time as it does for frost-tender annuals and non-hardy perennials. The ground will remain warmer than the air temperature for some time into late fall, but even so, you want to give the roots as much time as possible to anchor the plant against frost heave (cold periods that can push a poorly-rooted plant out of the ground, killing roots) and to grow extensively enough to supply the buds on the branches and any leaves (for evergreens) with enough moisture. When cold alone isn't responsible for killing a plant over the winter, insufficient soil moisture often is. Any plant kept in a container over the winter will be at much greater risk of having root damage due to freeze-thaw cycles (pots change temperature much faster than soil in the ground), and it will also dry out faster than an in-ground plant and need more attention to watering.

If a potted plant can't be planted in the ground quickly enough, such as the location is not yet vacated by another plant or there will be yard work like construction or utility work getting in the way, then try to heel it in. Heeling-in is simply planting a plant with the container still in place, rather than removing it. The goal is to insulate the root ball by having it surrounded by soil in the ground, not more vulnerable to above-ground temperature swings and drier conditions. Then, in spring, the pot can be pulled up and the plant either moved to where you want to display it (for longer-term potted plant displays) or the area it will be planted in is prepared (if needed).

If you have not yet purchased certain plants you wanted to grow, then you might want to wait until spring, especially since nurseries are rapidly running low on inventory as we approach late fall. (This is partly because they have limited space to overwinter the leftover stock in a way that both keeps them cool for dormancy but insulates them from the brunt of the weather.) Nurseries do tend to put excess stock on sale in late fall, so that can be a handy way to stock up on desired plants, but in that case, we suggest getting them planted in the ground rapidly so they can start to root-out. Mulch late plantings well, with up to 3 inches depth of mulch over the root zone (don't smother the crown, especially for perennials), which will slow soil temperature changes and the loss of moisture.

Miri