Winter-Flowering Annuals. It's important to understand that annuals are just what their name implies: Plants that grow, set seed, and die within a year. Although some plants grown in northern gardens are treated as annuals, many are truly tender perennials that simply can't survive the winter cold.
Annuals that do well indoors during the winter are limited to Coleus, Impatiens (including New Guinea), Nasturtium, Pansy Petunia, Verbena, Wax Begonia, Lantana, and Geraniums, with Coleus and Geraniums being the easiest.
Bright reds, soft pinks, sunny yellows –– these colors can still pepper your lawn, even when there's snow. You just need winter flowers that bloom in the cold. Viola, winter jasmine, calendulas, and many plants love cooler temperatures, and they don't hesitate to take advantage of winter's pollinators.
Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation.
You have two options when it comes to winterizing a petunia plant. The first is that you can put the plant into a state of dormancy somewhere that it's protected from frost, such as in a garage. The second is to treat the petunia as a houseplant, and keep it alive in a sunny spot indoors.
Some cool-season annuals can tolerate soil temperatures as low as 45 degrees Fahrenheit; however, most cool-season annuals will grow best in soil temperatures at 65 degrees Fahrenheit or warmer.
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.
Christmas Rose. This evergreen perennial blooms from winter to early spring depending on the selection and where you live (mostly early winter in warmer regions, and as late as February or March where it's very cold).
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.
Temperature And Humidity
Impatiens don't tolerate cold weather and will wilt and die once frost arrives. Don't plant impatiens outdoors until after the last frost of spring; it's best to wait until nighttime temperatures remain at 50 or higher.
Rejuvenating impatiens that have become leggy and overgrown is as simple as a quick pruning. First, in order to keep your plants blooming all summer, pinch off the tops of stems after each flower has bloomed and faded. This deadheading encourages new blooms. You can do this regularly throughout the growing season.
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.
Temperatures below 32 degrees can freeze the leaf tissue of cold-wimpy plants and turn them to mush after just a few hours. Some of the most tender annuals and veggies might not die but suffer cold-induced setbacks even when overnight lows dip below 40.
So what's the solution… Focus on frost hardy annuals. Some of these annuals that can withstand 20 degrees or so, including pansies, snapdragons, dianthus, alyssum, dusty miller, viola, and osteospermum. Keep in mind that flowers may be a bit ragged after such cold but the plants should make it through ok.
Pansies are surprisingly hearty in cold weather, though. They'll survive a frost, bouncing back from even single digit temperatures. If the blooms wither in the cold, the plants will often stay alive to bloom again, which makes them a great flowering plant for fall and early winter color.