After several hard frosts, remove spent flowers and stems by cutting stems off near the base of the plant, allowing the crown (base of plant) to remain. Bypass pruners are preferred because they make a clean cut through the stem of the plant, whereas anvil pruners crush the stem, leaving more damage behind.
Many pests and diseases will persist in the soil and plant debris over winter, if they're given the opportunity. Removing spent annuals and vegetable plants from the garden, improves our chance of eliminating numerous future pest and diseases that would otherwise survive on that dead plant material.
Wait to prune spring flowering plants right after they bloom. Any of your annuals that are no longer attractive can be either cut off at ground level or pulled out of the ground now. Or you can wait until later in the fall or even next spring. Here is a mix of annuals and perennials in early November.
Remove Most Annuals
In general, these plants are easy to spot because after the first hard frost, many of them, including impatiens, begonias, and coleus, have withered and turned brown. If the spent foliage and blossoms on these plants are free of mold and disease, we put them in the compost pile.
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.
You can put them in a garage or shed that gets cold but doesn't freeze, ever. They will over-winter as live but semi-dormant plants. Keep the soil just moist, not letting the potting medium shrink and pull away from the pot edges.
If you can decide, the best way of determining when to transplant is based on the flowering pattern of each plant. If your perennial blooms in the spring or early summer, it should be transplanted in the fall. If your perennial blooms in the late summer or early fall, transplant it in the spring.
If your flowers or leaves have spots, mold, or fungus, go ahead and discard them in the trash bag. You'll also want to throw out the soil that held these plants. Adding these to your compost could spoil the entire batch. But for any plant that was healthy before it died, add the remains to your compost bag.
Late fall is the best time to winterize perennial plants. A hard frost can be the signal to prep the beds for winter. If below-freezing temperatures are forecasted overnight, or you wake up to frost on the ground, it's likely a good idea to winterize your perennials within the next few weeks.
Cutting back perennials in the fall is not only a great way to keep flowerbeds looking neat and tidy through winter, but it also aids greatly in keeping plants vibrant and blooming the following year. Removing spent foliage and blooms helps a plant focus on recharging it's roots and resources.
Annual cleanup
Remove all of your summer annual flowers, including their seed heads, from your flower beds. (Throw these in your compost bin.) This does more than save you time next spring. Leaving annuals in your beds over the winter will invite pests and disease as the plants decompose.
True annuals and plants that we grow as annuals (considered tender perennials in southern regions) cannot survive cold winter temperatures. But there's no need to say farewell to these plants forever! Many “annuals” can be brought inside, even tender plants that need a winter dormancy period.
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.
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.
Leave Leaves for Wildlife
Fallen leaves also provide wildlife, especially pollinators, with some winter cover. Bees, moths, butterflies, snails, spiders, and dozens of arthropods and pollinators overwinter in dead plant material for protection from cold weather and predators.
Frost-killed annuals and vegetables can be pulled and composted – if they're not diseased. If they are diseased, bag and toss them.
"true" annuals that die at the end of year one after producing new seed. Species such as begonias, coleus, fuchsia, Persian shield and most houseplants will overwinter if you keep them above freezing. A few start to suffer when temperatures drop below 40. So get them inside in the next couple of weeks.
Simply put, annual plants die in the winter season so you must replant them every year, while perennials come back every year so you only plant them once.