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.
Your annuals need lots of sunlight in order to survive the winter season, and so placing your plants in the brightest spot of your home will ensure they thrive. A windowsill that receives plenty of bright light will do!
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.
"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.
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.
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.
Remove dead annuals from containers and beds. Like vegetable debris, they could harbor pest issues and the coarse stems make them difficult to compost, so toss it in the yard waste container. Perennial plants are a little trickier when it comes to fall clean-up.
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.
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.
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.
An annual plant completes its life cycle in one year.
The goal of every annual is to set seed and ensure the survival of the species. Once seed matures, the life cycle is complete, and the annual plant dies. Other annuals have their lives cut short before they can set seed because frost arrives.
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.
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.
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.
If you are blessed with a greenhouse or have ample window space, the easiest way to overwinter your annuals is to bring them indoors before they are killed by frost. If, like me, you only have a few windows you can take cuttings of these plants (except for Oxalis) and root them on your windowsills.
While some plants can survive light frosts, others will die as soon as their cells freeze. Depending on their hardiness, some potted plants will respond to the first frost by going dormant just like garden plants do. However, as the temperature continues to drop, their roots might die unless they are protected.
Annuals sprout, bloom, produce seeds, and die all in one growing season–unlike perennials which live for more than two years.
Planters made from modern substances, like fibreglass, fiberstone, and non-porous plastic composites can safely remain outside over winter. Fiberstone planters are made from a mix of limestone and fibreglass, which forms a material that looks like stone but weighs a fraction of the natural material.
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.
All cold tolerant annuals can best handle temperatures below zero (to minus two or three) at night when they are well watered in the day. If it is extremely cold, watering off the frost prior to sunrise will eliminate damage to the plant.
Know Your Frost Dates
In the fall as temperatures start to cool, the first day of the year that a frost occurs is considered the first frost date. As the temperatures continue to cool, the first freeze date of the year will occur (this is what kills most annual plants).
For some plants, such as pansies, stock and snapdragons, stress from summer heat turns off the initiation of flowers. But most flowering annuals are fairly heat tolerant and can be revived with a little pinch of their stems and a sip of nutrients.
Annual flowers grow for one long season, often into the fall, then die with the onset of freezing weather. With perennials, the above-ground portion of the plant dies back in freezing weather, but re-grows from the base and rootstock the following spring to bloom again.