Plants that are at least two zones hardier than your growing zone should be able to survive the winter outdoors in containers. You might need to provide some extra insulation and be certain your container is made from a frost-tolerant material.
Despite the fact your plants are dormant and brown, they should still be watered periodically. Plants that remain dehydrated in winter months often don't survive until spring. Not only does this create extra landscaping costs in warmer months, it can actually damage your plumbing.
Frost Advisory - This is when the temperature is expected to fall to 36 degrees to 32 degrees Fahrenheit. Freeze Warning - This is issued when there is at least an 80% chance that the temperature will hit 32 degrees Fahrenheit or lower. Light freeze - 29° to 32° Fahrenheit will kill tender plants.
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.
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.
Bed sheets or comforters work best for covering large plants and shrubs. Newspaper can be used on low-growing foliage, but it can often be difficult to get it to stay in place. You can also use old pillowcases, sheets, towels and even cardboard boxes.
When should I wrap my plants for winter? This Old House landscape contractor Roger Cook suggests to start wrapping your plants in November. If your plants are new, be sure to cover them for the first two years. The older your plants get, the sturdier they become in surviving winters.
Compared with their garden-grown counterparts, container-grown plants are at a severe disadvantage when cold weather arrives. Though hardy plants have developed foliage, stems, and branches that can withstand very low temperatures, their roots are far more sensitive and vulnerable to freezing.
A covered porch usually provides protection from light frost, but the garage or sun room is better for freezing temperatures. A couple days in darkness won't hurt the plant. Or move them out during the day and back in at night, if cold temperatures persist.
Throughout the winter your plant is still going to need some water. If the soil gets completely dry, the plant can die of desiccation. While regular watering isn't necessary, monitor the moisture level and water if the soil is dry.
The key to success with garage storage is that this area is attached to the house but not heated. The garage never goes below 32 degrees but tends to hover in the 40's and low 50's all winter. This keeps the plant dormant but the plants never freeze. Watering is needed, but not too much or too often.
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.
Mulch helps keep plants moist and warm and protects the roots of newly-planted trees, shrubs, flowers and vegetables. If frigid weather suddenly crops up in Northern Utah, make sure your plants have the right amount of mulch.
Skip Watering if: The ground is frozen. There's a hard freeze (at least 4 hours of 25 degrees F) The temperature outside is under 40 degrees.
Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants. Evergreen foliage can also be protected from excess water loss using anti-desiccant sprays. These sprays are sold at most garden centers.
Know Your Plants' Cold Tolerance
Some frost-tender plants need to be covered as soon as the temperature hits 32°F, while others can handle lower temperatures and/or longer freezing periods. You'll need to look up each of your plants to verify its cold tolerance.
In cold weather, water should be trickled slowly into the soil. Water only when air temperatures are above 40 degrees F. Apply water at mid-day so there is time to soak in before possible freezing at night.
Most outdoor plants can go without water for about a week. Container plants are the thirstiest. Most need to be watered daily. If you're planning to be away, adding mulch around flower and vegetable beds helps keep moisture in longer — even if it doesn't rain during your absence.
It can be tricky choosing when is the best time to water plants in winter. Avoid watering early in the morning or late at night, keeping to the middle of the day wherever possible as the soil around plants should be dry at night.