Protect tender plants from winter freezes

Richard Bogren, Owings, Allen D.  |  12/11/2015 11:04:31 PM

When a freeze is coming, cover tender plants with cloth that’s supported to prevent breaking the plant and secure the cloth at ground level to keep out the cold. (Photo by Dan Gill, LSU AgCenter)

Morning frost creates a layer of white in the sun garden at the LSU AgCenter Hammond Research Station. (Photo by Allen Owings, LSU AgCenter)

Southern sugar maples provide fall foliage color in Louisiana. (Photo by Allen Owings, LSU AgCenter)

News Release Distributed 12/11/15

By Allen Owings

LSU AgCenter horticulturist

HAMMOND, La. – Winter is here, and this time of year brings questions about protecting landscape plants during the cold months of December, January and February. The best approach to protecting plants in winter is to pay attention to the weather forecasts and try to know a couple days ahead of time when a freeze is approaching.

This year our first frost came a little late or right about on schedule, depending on your location in the state. Temperatures at first frost in some areas, however, also resulted in a first freeze. It was 29 degrees when frost first occurred in November at the LSU AgCenter Hammond Research Station.

Weather conditions prior to a freeze or frost play a role in how these temperatures affect plants. If the first cold event is a freeze, landscape plants will suffer more damage. If several cold fronts move through an area and produce several frosts prior to a freeze, we will see fewer negative effects on plants that normally show damage.

One benefit of a gradual decrease in fall temperatures is more attractive foliage color on trees and shrubs in Louisiana landscapes. Also, plants that bloom in fall, such as sasanquas and fall-blooming azaleas, flower better, longer and earlier when this occurs.

To prepare plants when a freeze is forecast, thoroughly water them if the soil is dry. This is especially important for container-grown plants. Shrubs in landscape beds also can be helped with irrigation prior to a freeze. This does not need to be done the day or night before. Rather, adequately hydrate plants gradually during the fall months and then three to five days before a major cold event. Wetting plant leaves before a freeze does not, however, provide any cold protection.

When a freeze is coming, move all tender plants in containers and hanging baskets into buildings where the temperature will stay above freezing. If this is not possible, group all container plants in a protected area like the inside corner of a covered patio and cover them with plastic.

For plants growing in the ground, mulch them with a loose, dry material such as pine straw or leaves. Mulches will only protect what they cover and are best used to protect below-ground parts and crowns. Or they may be used to completely cover low-growing plants to a depth of 4 to 6 inches. But don’t leave a complete mulch cover on for more than three or four days. Many folks heavily mulch their tropical hibiscuses in landscape beds using this method. Smaller individual plants can be protected by covering them with various sizes of cardboard or plastic foam boxes.

Larger plants can be protected by creating a simple structure and covering it with fabric or plastic. The structure keeps the cover from touching the foliage, preventing broken branches and improving cold protection. For example, you can use several stakes slightly taller than the plant or use last season’s tomato cages. The cover should extend to the ground and be sealed with soil, stones or bricks to keep out the cold. Plastic covers should be vented or removed on sunny, warm days.

For severe freezes when temperatures dip into the teens, providing a heat source under the covering may help. A safe, easy way to do this is to generously wrap or drape the plant with small outdoor Christmas lights. The lights provide heat but do not get hot enough to burn the plant or cover. But be careful and use only outdoor extension cords and sockets. If necessary, you may prune a large plant to make its size more practical to cover.

Keep in mind that cool-season bedding plants are adapted to the normal cold winter temperatures, so cold protection typically is not needed. Also, the vast majority of shrubs and trees in our landscapes are very cold hardy. We would not be planting them as permanent additions to a landscape if they were not. Educate yourself on plants that are in your landscape and learn which ones will have more trouble with winter temperatures and growing conditions.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren

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