Depending upon where you live (zonally), there are ways of winterizing your perennial containers. Folks that have winters in zone's higher than 6 (7,8,9) - you are blessed. Those of us that hover over the mid 5 zonal range or lower (4,3,2), our winters are generally too tough to overwinter perennials in containers.
With my perennial planters, I have a few choices here near the Greater Toronto Area. Depending how close you are to Lake Ontario, (our 5b, 6a zonal situation) and how a severe or mild winter we will have - the overwintering results will vary.
One thing to make sure first before trying to overwinter any pot outdoors is to make sure it's a winter tolerant pot/container. Terra-cotta, some concrete and porous materials will bust from frost expansion.
1. Place your containers on a south facing brick wall and line them up close to each other. This helps to insulate them and allows for a solid freeze when they are touching each other. The brick wall will radiate heat and keep them slightly warmer than a cold corner. Be sure to keep them well watered.
2. Place your perennial filled containers in the garage. I have placed mine on the side of the garage which butts up against the house. This is the warmest wall and the most safe for overwintering. I usually raise them off the floor with upside down buckets or rubbermaid containers. This just keeps them off of the cold floor and gives them a chance to be well drained before going dormant. I don't water them as often. Only when they are bone dry. Reason: they can rot otherwise.
3. Group several containers together. Water these containers if they remain outside. Most containers freeze and thaw several times before winter arrives. This causes whatever plants are left to desiccate and also the soil left to dry out. I usually soak my containers well before switching the outside water off completely. I also in a pinch, take snow (without salt) and heap it over my containers when I see they are dry.
4. This is my method this year: I dissemble the perennials and plant them back in the garden to overwinter. I usually do this in late September for sensitive perennials, like some astilbe's. This just prevents certain loss if you are unsure. Come spring you can transplant them back in your pot, knowing they have overwintered well in your garden beds.
|Here, I just cut back all the bulky, dry stems from the Rudbeckia and Astilbe. This makes it easier to seperate.|
|I made 3 sharp cuts into the pot with my trowel and this Astilbe popped out with ease.|
|These are the 4 perennials I wish to overwinter in my garden. Rudbeckia fulgida 'Goldstrum', Hosta 'Hideout', Hosta sieboldii and Astilbe chin. 'Visions in Pink'.|
The finished container:
The 4 perennials, I tucked back into areas of my backyard and watered them well. They will pop back up in spring to either be part of my perennial planter again, or moved to their new home elsewhere.
One sure perennial that seems to winter over, no matter how severe the winter - is my Lamium. They are tough as nails. I will leave both types of Lamium in my container and I am sure I will see their return in the spring again.