Three good reasons to leave some perennials alone for the winter:
1) I'm lazy.
2) I'm messy.
3) Bizarre mountain micro-climates.
We measure snow in feet, not inches, but that doesn't mean it stays put. Intense mountain sunlight melts the snow in certain parts of my yard. If I leave flower stalks standing tall, more snow drifts around the plant, creating a warm blanket.*
To chop or not to chop....
Beebalm - Birds love the seed heads but this perennial succumbs to mildew very easily.
Lilacs - began working on next year's flowers months ago. Pruning in the fall will break your heart. No fragrant blooms come spring!
Catmint bushes green up very early in spring. Trimming them back clears the way for earlier, more plentiful blooms.
Columbine's dead foliage can stunt their growth the following summer.
Hollyhocks suffer mightily from 'rust,' a fungal disease that overwinters in debris. Plus, they're hell-bent on taking over the world. (Or, at least your garden.) Removing stalks and seeds keeps you in control.
Penstemon & Salvia: Native plants prefer dry soil. Dead winter foliage gets soggy, provides too much moisture and stunts summer growth.
Cheating death in snowy climates.
Snows provide great insulation in winter. (That's why Eskimos invented igloos!)
A Utah study measured January temperatures above and below 3 feet of snow pack.
- Above the snow it was -10 degrees. (F)
- Below the snow pack the temp was +17 degrees (F,) meaning perennials were basking in a comfy zone 7 climate.