I now live in the city with only a balcony to grow plants. I greatly miss the peonies I used to grow in my country garden. The soil was a mixture of clay and loam.
I never lost a single one and they didn’t protest when I transplanted them. Winter temperature sometimes went below 30 degrees.
What would happen if I planted one in a deep pot, following the rule to keep the root near the surface and tried to winter it. On the balcony I use a loose potting soil which would not work for peonies. What soil should I try or is this a completely idiotic idea anyway?
Thank-you for contacting Toronto Master Gardeners with your question about growing herbacious peonies (Paeonia lactiflora) in containers. This is not an idiotic idea!
The most important consideration will be pot size. It has to be large. Most sources recommend at least 18 inches tall and wide, preferably even larger. The potting medium is also important. Peonies are tough plants but they do need good drainage or they can succumb to rotting of the tubers/roots. A mix of 2/3 topsoil and 1/3 perlite or vermiculite should give you the drainage you need. Make sure your pot has several drainage holes. As you note, planting depth is crucial to ensure blooming (ie. eyes no more than 1 1/2 inches below the soil surface). You will also need to fertilize your peony in the pot. Any balanced perennial flower fertilizer should work.
I am assuming that your balcony receives a reasonable amount of sun. As you know from your experience with peonies in the garden, they do need sun. The sources I consulted, however, suggest a dappled sun or part day of sun is better than a full sun exposure with potted peonies.
A final issue to consider is over-wintering your potted peony. While peonies do require a cold period for flowering, and your potted plant should be able to withstand a fair amount of frost and cold, it may need some protection from a deep freeze. You could place it in a corner, away from the wind, and wrap the pot for some additional insulation.
Here are some general resources on growing peonies in containers:
https://www.gardeningknowhow.com/ornamental/flowers/peony/growing-peony-in-container.htm
https://homeguides.sfgate.com/grow-peony-pot-41756.html
Good luck with your balcony peony!