Perennials NOT to Cut Back
Also, do not cut back hardy perennials like garden mums (Chrysanthemum spp.), anise hyssop (Agastache foeniculum), red-hot poker (Kniphofia uvaria), and Montauk daisy (Nipponanthemum nipponicum). Leave the foliage. It's important to protect the root crowns over winter.
I usually go through and lightly rake my flower beds at least once in the fall and that cuts down on the amount of clean up I have to do in the spring. If you have a problem with rotting perennials or rotting bulbs, it's especially important to get as much leaf debris off your flower beds.
While many gardeners believe that fall cleanup is the only way to go, there are actually several benefits to leaving a majority of cleanup for the spring. Since many animals and insects are adapted to use plants for winter survival, it makes for a healthier garden to keep their needs in mind.
Unlike perennials, annuals do not come back from season to season so there is no reason to leave these in the ground. Pull them up, roots and all, and add them to your compost pile. Remove weeds and leaf debris. These are common places for diseases and pests over winter.
Mulching Tender Perennials
As with extra mulch, place the protective layer late in the fall season and remove it in early spring. A 6- to 8-inch-layer should be adequate for most perennials.
We suggest waiting to clean up your yard until most of the leaves have fallen; otherwise, you'll have to do it multiple times throughout the season.
When To Clean Up The Garden In The Fall. The best time to start your fall garden preparation is after the first few freezing nights have killed back much of the flowers and foliage on the plants. Of course, you can start earlier than that if you want to. But be careful starting too early.
Some species of native pollinators, like this docile leaf cutter bee, overwinter in hollow plant stems. Again, waiting as long as possible to rake leaves out of perennial beds is the best idea. Hold off on your spring garden clean up until daytime temperatures consistently reach the 50s, if possible.
It's important to cut back foliage in the fall to protect flowering plants from disease and give them a clean start for regrowth as winter starts to turn into spring. However, there are some plants you can keep around through the winter since they benefit wildlife and still offer visual interest for your home.
Don't shear the branches of spring flowering shrubs (Forsythia, Lilac, New Mexico Privet, Spirea, Flowering Quince, and others). These shrubs produce flowers on last year's wood, so removing old growth will reduce or prevent flowering. These plants should be pruned immediately after they are done blooming.
The Birds:
Not cleaning up the garden means there will be more protein-rich insects available to them during the coldest part of the year. These birds are quite good at gleaning “hibernating” insects off of dead plant stems and branches, and out of leaf litter.
Excessive leaf matter on your lawn going into winter is bad for several reasons. First, it will smother the grass and if not removed very soon in the spring it will inhibit growth. Second, it can promote the snow mold diseases. And finally, turf damage from critters (voles, mice) can be more extensive in the spring.
If you don't rake them, your grass will smother, invite pests, and breed fungus that can spread to the whole lawn and garden. Removing the leaves gives your lawn a chance to soak up the sun and warmth before the grey winter season.
Fallen leaves, as an additional physical layer of organic materials above ground, provide food, shelter, and nesting or bedding materials to a variety of wildlife, as well as overwintering protection for a number of insects, all of which work together to contribute to a healthy yard.
If self-sowers play a large role in your plantings, skip fall mulching. That fresh layer could interfere with seed germination in spring. The biggest challenge with fall mulch is that you need to squeeze the job in on weekends, especially in areas that practice daylight saving time.
If you smother a perennial in mulch, you upset the plant's biology and run the very real risk of keeping the crown wet during winter dormancy, and it will rot. I avoid organic mulches on perennials that need free drainage and good air circulation, such as bearded irises, lavenders, rosemary and sages.
Fall mulching saves time and energy in the spring because it cuts down on the need to weed. It also saves you the labor of spreading new soil and mulch after winter snows. You may also save money too. Mulched perennials are likely to last the winter, reducing your outlay on new blooms.