Advice for overwintering perennials in containers?
We have many different perennials in containers we'd like to overwinter for next year. These include herbs, such as mint, thyme, nepitella, rosemary, etc. We also have hummingbird sage and salvia in a couple of pots. We don't have any sunny spots indoors. Is there a way to keep them going through the Winter months?
Prince George's County Maryland
There are a couple of general guidelines and options for overwintering perennials in containers. A good rule of thumb is that you can overwinter perennials that are winter hardy in two zones colder. So, for example, if you are in USDA hardiness zone 7, you want to have perennials that are hardy to the colder zone 5. (You can find your hardiness zone here, https://planthardiness.ars.usda.gov/PHZMWeb/). A plant such as hummingbird sage (Salvia spathacea) is winter hardy in the warmer zones 8-11. It will grow here in the summer but is not likely to survive in the winter (in the ground or a container) -- unless we have an unusually warm winter (possible, but not predictable). The perennial herbs should overwinter in containers. Rosemary can be a little tricky; it does not do well over winter if the soil stays too moist.
There are several ways to provide winter protection for container plants:
- Place them in an unheated garage or shed after the hard freeze (check on their moisture periodically)
- Group your pots together in a sheltered area away from prevailing winds and cover them with evergreen branches or put bagged leaves or mulch around the base for insulation
- Put the containers temporarily into a pit in the ground to insulate the roots and add mulch around them for extra insulation
- Wrap the base of your containers in bubble wrap or thermal blanket material.