I live in Ottawa, and would like to do some container planting with ornamental grasses, specifically Hakonechloa macra ‘Aureola’ or Golden Variegated Hakone grass.
I have no space to sink the plants into the ground for the winter.
Is there another way to winterize the container or a hardier grass that can stay in the planter all winter?
Winterizing containers can be tricky and some simple tips will help you through to getting a long lasting year round decorative urn. The combination of plants and retrofitting your urns or planters with Styrofoam or winterizing materials can be a trial and error but there are sure ways to help the process of winterizing the urns. You need to select containers that are large enough and have enough volume of good-quality container soil mix to support these grasses. And then be sure to select plant materials that are a zone or two hardier than the zone you live in, which in Ottawa is Zone 4b. Golden hakone grass is hardy in Zone 6, so it likely won’t survive in a container (though there are exceptions to every rule). You would need to choose plants that are zone 2 for your winter urns if you want plant material to survive in them for next spring. Good drainage is also necessary as is making sure they get adequate water up until the soil freezes in the planter. The materials that your planter is made up of has a direct connection to the weatherization of it. Composite plastics, metal, and concrete are the most durable, long lasting, and can resist temperature fluctuations. You then line the inside of the container with a 3″ thick Styrofoam. Leave a two inch space from the top of the container so the Styrofoam doesn’t show when the soil settles around the edge.You can get the Styrofoam from any building supply or hardware store. Cut it to the size of your planter walls and just line them by placing the styrofoam inside. You then back fill with more container soil. Mulching the containers in the fall will also help insulate the plant materials and provide moisture retention. And if possible, for winter, group the containers together in a sheltered spot out of the prevailing wind–especially important on a balcony. You can even wrap them all in bubble wrap to provide additional insulation.
If you google “Grasses for Zone 2” you can find all kinds of suggestions for what might do well, including online catalogues for nurseries that specialize in cold-climate plants. Good luck!