Tips & Techniques to Overwinter Perennials in Containers
I garden in Zone 5 and love container gardening with perennials. There are a number of great garden plants for containers including the likes of Hostas, Heuchera, and ornamental grasses for shade. In sunnier spots, I love to mix and match different groundcover like Sedums and Delosperma. But by the time the killing frosts have knocked my perennials dormant, it is time to tuck away my favorite perennial pots for the winter to insure their welcomed return next spring.
Overwintering fact: Your overwintering success with container perennials is dependent on the ability to insulate the roots (containers). Plants grown in containers are exposed to colder temperatures than those grown in the ground and are considered at least two zones colder. I live in Zone 5 which would make my pots a Zone 3.
How I've Overwintered Perennials in Containers
I’ve gambled and left pots out all winter and some made it and some did not. So what do I need to do to make sure my potted perennials come back next year? I do recommend (particularly in colder zones) to consider the following:
This is an old nurseryman’s technique for overwintering pots and bare root plants. I dig a trench deep enough so my tallest container is level with the soil line. I group all my pots together in this trench and fill it in with the leaves I haven’t raked up yet. Burying your pots will help insulate the roots
No time to dig? – so again I’ve grouped all my pots tight together and covered them with either a thick layer of leaves or potting soil.
Knock ‘em over
Knock 'em over on their sides. Here, you are keeping your roots warmer by laying them down You will want to group them together. You can also cover them with leaves for some extra insulation. I find this is especially helpful with Hostas pots. I have lost potted Hostas not so much to the cold, but to late winter when the snow melts and creates a freeze/thaw effect which kills new emerging eyes. Simply laying pots on their sides minimizes this problem.
Bring ‘em on in
You will want to bring inside anything grown in a ceramic pot, or it will truly go to pot next spring cracking into hundreds of pieces. I have stored numerous containers against a wall in my garage (a cellar would work). The important thing to remember here is that plants do dry out and you will need to give them a drink by January or February and monitor them thereafter.
You might have your own methods of overwintering that have worked for you. (please drop us a line - we'd love to hear about it)
Please visit our section on Garden Plants for Containers for additional ideas for your perennial container garden.