I had huge, beautiful perennial beds when I lived in NW Montana and the
winters would have been much harsher than yours, I would assume. Other than
my window boxes I didn't plant annuals. I never fertilized the first year I
planted divisions. I amended the spot with screened compost, planted
divisions, watered well, no fertilizing. I also didn't mulch my flower beds.
I'm of the 'survival of the fittest' school. They all seemed to survive just
fine. Perennials establish roots the first year they are in the ground. If
you fertilize for lush top growth they don't put down the heavy root growth
they need, or so I was told during my gardening infancy and that seemed to
always work for me. For established perennials I stopped fertilizing the
last weekend of July no matter what their bloom cycle was. July was also the
month I put down the last compost for the year. I cut back on watering the
end of August. I also never cut any plants back in the fall except the very
tall ones, like hollyhock and delphinium, and those I only cut back by half.
I did cleaning and grooming as soon as the snow melted off and boots didn't
sink knee deep in the Spring thaw mud. Maybe you are being 'too kind' to
your new divisions.

Val

"Eric" wrote in message
. ..
I have a large perennial garden here in zone 5. I am losing many plants
per year over the winter and all varieties are well suited to zone 5. Most
of the divisions I made from larger plants were lost over the winter and
these were large healthy growing plants. This past winter, the winter was
mild here in southern New York and I still lost a lot of plants. Any
ideas?