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.
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.
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.
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.
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. Here's a rundown of annual versus perennial.
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.
Generally speaking, the annual plants you want to protect or propagate should be brought indoors as the growing season begins to wane and before cold weather threatens to kill them.
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.
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.
CORVALLIS, Ore. – As fall approaches, consider letting some of your annuals go to seed. If the winter isn't too harsh, they may pop up next spring. Annual plants are inherently programmed to set seed and die in one year.
Be Sure to Harden Annuals Before Placing Them Outside
Any annual planted outdoors should be properly hardened to acclimate them to cooler temperatures. Those annuals that are hardened are more likely to survive a frost or light freeze with little to no damage than those that are not hardened.
Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation.
Steps To Care For Petunias in Winter
The plant will need to be brought inside in the winter in colder regions. Petunias can be allowed to go dormant, or you can try to keep the plant actively growing, but be aware that it can be hard to prevent dormancy.
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.
A few start to suffer when temperatures drop below 40. So get them inside in the next couple of weeks. True annuals such as vinca, zinnias and marigolds are eventually going to croak even if you try to milk them through winter.
After zinnias flower, cut off the old flowers (a process called “deadheading”) to encourage more flowers to form. Zinnias are annuals and will die with the first hard frost of fall. If you want them to reseed, let the last flowers of the season mature fully and scatter their seeds.
Winter Protection Techniques
If possible, find an area in the garden that you can dig up, and sink the pots into the ground so their roots will be insulated by the surrounding soil; then mulch heavily with straw, shredded bark, or leaves as you would other plants.
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.
Provide Additional Shelter. In addition to clustering your plants together, you can also cover the pots with a tarp, straw, or another insulating material. Doing so will moderate the temperature swings and increase the likelihood of your perennials surviving the winter.