This spring we planted maiden grass graziella in many containers around our patio. We know that this is a perennial that would normally return every year if planted in the ground. Our experience last year was that the grasses didn’t survive the winter. Is there a way we can save the plants? If we remove them from the containers now in October, and place them in the ground, would they survive winter? Or should I dig out the root balls and put them in containers and bring them in the house? Would that work? Thanks for your help.
I am sorry to hear that you lost your grasses last year. Maiden grass Graziella (Miscanthus sinensis ‘Graziella’ ) is lovely, and many gardeners happily treat these grasses as annuals, leaving them in containers over the winter, where they remain attractive throughout the season – then discarding them in the spring.
The main challenge with overwintering perennials – including grasses – in containers is that plants may not survive temperature fluctuations (freeze/thaw) that occur throughout the season. Perennials planted directly in gardens are not subject to these vast temperature changes, as the soil is a more even temperature.
I suggest the following as the best options for you:
- The best bet is to move the grasses into a hole in a sheltered area of your garden. You can bury the entire pot or just the plant itself. Mulch with leaves to keep the plants protected for the winter season. Then in the early spring dig them out and place them in a lovely container. You should move the plants shortly (it is October 24)
- Alternatively, after the first hard frost, move the pots into the basement, garage or other cool area. Although it’s not necessary, if you wish, you can give the grass a haircut – leave just a couple of inches above the crown. [You may want to save some of the grass stalks for indoor decoration]. Inspect the plant and remove damaged stalks. Ideally, there should be moderate light in the room (but not too much as you don’t want the plants to break dormancy), and water the plants sparingly to keep them evenly moist – just don’t let the soil dry out completely. In the spring, start hardening the plants off over several days.
And if you someday want to try and overwinter the grasses outside in their containers, here are a few pointers:
- Consider the “2-zone reserve” rule in selecting hardier grasses that have the best chance of surviving outside in winter. This rule provides that, although it is not possible to be certain that grasses will overwinter successfully in containers, if you select plants that are hardy to two zones colder than your area, they should nearly always survive outdoors in containers over the winter. For example, your Miscanthus is hardy to zone 5 (in the ground). In a container, it should endure zone 7 winters (i.e., unfortunately, not Ontario winters!).
- Use pots that require a large volume of soil. With all that soil, the plants (and their roots) will have a better chance of avoiding the freeze/thaw cycle and might pull through.
- Water thoroughly right before the ground freezes, to provide a supply of water the plants can use when the soil thaws. Mulch with leaves and add a few handfuls of snow from time to time; the latter will act as mulch and provide water during thaws. If you wish, you could wrap the pots in an insulating material, to give extra protection.
- Containerized perennials often get too much water throughout the winter season, as a thaw may not reach the drainage holes, and roots can end up sitting in water (and then ice). To get around this issue, overwinter the containers under a covered area so they won’t receive excess rain/snow. If you have a few containers, group them close together in a sheltered area (not on pavement or above-ground deck). Placing them under eaves by the east or south side of your house would be ideal.
- See the Toronto Master Gardeners’ Winterize ornamental grass in container for additional information, including the container materials to select for the best chance of overwintering your plants. Cornell University’s Winter Containers contains a lot of helpful information for overwintering plants in containers.
We have had a couple of additional questions on this issue in the past, that may be of interest to you – see Ask a Master Gardener: