Some plants can overwinter as houseplants. The most successful are: geraniums, Boston ferns, and tropical plants such as begonia, caladium, coleus, and hibiscus. For these plants, the general rule is to give them as much light and humidity as possible; keep away from heat ducts. Some will benefit from artificial light.
Many of the best plants for overwintering in a garage or basement have bulbous roots designed to store nutrients and moisture through a dormant period. Amaryllis, oxalis, cannas, dahlias, and tuberous begonias hold moisture in their fleshy bulbs, tubers and corms, so very little supplemental water is needed.
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.
1. In order to overwinter a perennial or shrub in a container outside, it needs to be two zones hardier than the zone you live in. 2. Perennials and shrubs that are in your zone or one colder can be overwintered in an unheated garage, buried in the ground, or transplanted.
An excellent way for home gardeners to over-winter container-grown perennials is to dig holes in a garden area and set the pots in the ground. After the plants have been placed in the holes, place soil around the pots as if planting them. Soil is a good insulator and will protect the plant's roots from extreme cold.
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.
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.
If it is not going to rain before the freezing temperatures arrive, you should water plants thoroughly. This is because moist ground stays warmer than dry ground. Watering the night before the freeze arrives will insulate the root structure of the grass and plants, decreasing the potential for cold injury.
On woody plants, the leaves will yellow and drop off. Keep the dormant plants dry, but not so dry that the soil becomes powdery. Check soil moisture often and if very dry, lightly water. In most situations, light watering will be needed every two to four weeks.
Overwintering Techniques
The general consensus seems to be that the best way to overwinter containerized perennials is to take the entire pot and bury it in the ground. This way, the roots are protected like they would be if the plants were actually planted in the garden.
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.
Annual Plants
Crabgrass, petunias, and snapdragons are types of annual that will not survive cold temperatures and will need to be cared for to survive winter.
Even an unheated garage or shed is typically enough to keep tender plants in an above-freezing environment. Potted tropicals and houseplants should move inside even if temperatures don't drop below freezing. Many of these suffer damage even at 40 degrees.
Cold weather-tolerant outdoor planters
Fiberstone plant pots are highly resistant and will endure extremes in temperature throughout the year. Plastic pots are less frost-tolerant than fiberstone versions, yet they are still much sturdier than those made of natural materials.
A fabric covering is best because it will allow moisture to escape while still protecting your plants from frost. Fabric coverings will prevent the freezing air from coming into direct contact with the moisture on the plant while also capturing the heat that is radiating from the ground.
A space heater or solar lamps is all you need to keep the garage warm enough for plants to thrive. Keep in mind that the hotter the room is, the more light and water your plants will need.
It depends on the temperature, and specifically the nighttime low temperatures. You'll want to move your houseplants indoors before night temperatures get below 45°F. Any colder, and you're likely to see damage, especially on tender new leaves and stem tips.
Whether it's hostas, daylilies, ornamental grasses, evergreens or everbearing strawberries, not only can perennials provide big interest and color in their pots, they also have the advantage of being able to grow again year after year. Well, that is, as long as you can protect them over winter!
Plants and perennials that require additional protection to survive your winter will need a deep layer of mulch added by mid November or later, when the ground is beginning to freeze. Do NOT add deep mulch too early or your plants will not be slowly exposed to colder temperatures, allowing them to acclimate for winter.
Heated Greenhouses with Roll-up Sides
This method requires minimal fuel and results in very few plant losses. To use this method, perennial houses are heated to 50°F until all of the plants are well rooted, then the temperature is slowly decreased to 35°F so the plants will vernalize and flower in the spring.
Perennial Flowers: Most perennial plants do not suffer frost damage and do not need to be covered. Frost sensitive perennials include Hostas and Bleeding Hearts. They should be covered to protect their foliage and flowers. Cover any blooming or budded up perennials.