Continue to water annuals until freezing temperatures kill them. If your annuals are in containers, move them into a garage or other protected space when temperatures are forecast to dip into the 40s overnight. You can do this until daytime temperatures no longer rise above that threshold.
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.
How to Overwinter Annuals by Taking Cuttings. Another way to overwinter annuals—and the only viable method for true annuals—is to take cuttings from your existing plants. This can also be the best method for tender perennials that don't adapt well to transplanting, such as coleus and begonia.
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.
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.
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.
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.
"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.
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.
Your annuals are like a champion boxer – they more you try to knock them down, the tougher they get. If you trim off a quarter of their growth a couple times a year, they come back bigger, stronger, better, and more gorgeous.
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.
Petunias Winter Care in Pots
Getting the potted plants out of cold temperatures and into a basement or garage can protect the roots so that the plants will grow again in the spring. Trim back overgrowth and water when the soil dries out.
You can overwinter potted perennials in an unheated shed or garage. Allow them to naturally go dormant in the fall before moving them inside. Then put them back outside once the weather starts warming back up in late winter or very early spring.
Tender annuals — Tender annuals thrive in warm soil and warm air temperatures. They should only be planted once temperatures reach and stay above 55°F. They can be severely damaged or die if they are exposed to frost or temperatures below 32°F.
To extend the beauty of your garden into autumn and put some color back into your landscape, consider planting some cold-tolerant annuals. Many of these can take temperatures to 20° F. As our seasons change, so can your garden by highlighting these beautiful tough plants in your beds, borders and containers.
Take Special Precautions for Potted Plants
To protect them, you can wrap the pots in an insulating material (think burlap, old blankets, or even bubble wrap), place them close to the foundation of your house, and arrange them close together. You can also put a layer of mulch over them for added protection.
Most potted or hanging plants, like petunias, are fine as long temperatures don't dip below 39 degrees, and especially if the temperature doesn't dip to the freezing mark.
Frost and Freeze Protection in the Spring
Vegetables, annuals, and tropical plants planted outdoors early in the season are the most important plants to protect during a late frost or freeze event in spring. Protecting emerging spring bulbs and perennials is not necessary.
Shape and reduce the size of overgrown and bulky plants by cutting unwanted stems to the base of the plant or where stems meet. Typically, it is good to remove up to one-third of the stems, especially in overcrowded areas where the foliage is beginning to discolor or die.
Annuals typically flower and bloom in the spring and then wither and die around autumn. Unlike perennials, annuals do not regrow the next season—at least not from the same root. Instead, annuals must be replanted each year—or, in some cases, the seeds left behind may successfully sprout new plants.
While there are benefits to waiting till spring for cleanups, there are still some reasons when fall is best. As a general rule, if you are cutting back in the fall, wait until leaves and stems turn brown — this is a sign the plant is dormant and will not send up any tender, new growth before the first frost.
Spring flowering shrubs and trees.
Shrubs and trees like lilacs, azaleas, and others will grow best when they are pruned right after they flower in the spring. Avoid pruning them in the winter as it may stunt their growth.