Another good idea is to remove annual flowers after a killing frost. In addition, perennials that show signs of disease should be cut back in the fall.
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.
For instance, you could cover the plant with an old comforter and then a sheet of plastic. No matter what you use, it is important to uncover the plant after the threat of frost has passed so the plant can get light as well as to prevent heat build up under the canopy once the sun comes out.
Cover Plants – Protect plants from all but the hardest freeze (28°F for five hours) by covering them with sheets, towels, blankets, cardboard or a tarp. You can also invert baskets, coolers or any container with a solid bottom over plants. Cover plants before dark to trap warmer air.
Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation. Severe or hard freeze - 25° Fahrenheit and colder causes heavy damage to most plants.
Cutting back of dead or dying top growth is the only maintenance that is needed for winter preparation. Cut the stems down to the ground, or to the basal growth if you are gardening in the warmer hardiness zones. Alternatively, the flower stems can be left to cut back in the spring.
Fresh Flowers & Roses should not be placed in either the refrigerator or the freezer! The Refrigerator generally hosts a variety of fruits & vegetables that emit ethylene gases which can shorten the life or even kill your fresh flowers & roses. The Freezer is simply too cold!
Move Containers Indoors
Small container gardens and any plants still in their nursery containers are generally easy to move indoors temporarily. A heated location isn't always necessary. Moving plants to a space like a garden shed or growing plants in a garage will provide enough protection when it gets cold.
Some perennials, like hostas, peonies and daylilies, need to be pruned in fall to avoid winter damage. Plants like these should be pruned after the first few frosts in late fall or early winter. Other perennials like mums and coneflowers are better off being pruned in spring just before new growth comes in.
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.
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.
When Should You Cover Plants? Cover your plants at night and remove them during the day when the temperatures rise above 32 degrees F, so that the soil can warm up again.
Yes – if you secure the plant properly. Garbage bags work to cover plants and protect from frost, but they must not be allowed to touch the plant's surface. Use stakes and supports to create a tent-like structure over the plant, which will retain warm air. Make sure the trash bag goes all the way to the ground.
However, know that even if air temperatures are as high as 38°F, frosts may occur on the ground and on plants. It's better to protect plants just in case!
When the weather forecaster warns of an overnight freeze, cover your plants with burlap, an old sheet or blanket, or clear plastic. Use stakes or another support to keep the covering from directly touching the plants.
Plastic can be used to protect plants from frost, but it's not the best or most effective material. In fact, the horticultural experts here at Green Impressions actually recommend against it. Plastic materials such as vinyl and traditional camping tarps aren't breathable, causing moisture to get trapped inside.