No matter whether plastic or cloth, covers for outdoor tropical plants should be secured at the ground.

Greg Sevcik uses plastic bags to cover plants in the front yard of the home of he and wife Leslie Blanchard, Sunday afternoon, Feb. 14, 2021 to prepare for a hard freeze forecast for Monday night in the Baton Rouge area.

No matter whether plastic or cloth, covers for outdoor tropical plants should be secured at the ground.

Garden columnist Dan Gill answers readers' questions each week. To send a question, email Gill at gnogardening@agcenter.lsu.edu.

What is the best covering material to use to protect outdoor plants from the cold air, fabric or plastic? — Greg Smith

The cold weather last weekend has put protecting tender plants in our minds. Either type of covering may be used, and each has advantages and disadvantages. A simple cover can significantly reduce cold damage when temperatures are in the mid- to upper 20s.

Plastic is lightweight and easy to use. If it is rainy, plastic does not absorb the water and get wet and heavy. However, wherever a leaf of the plant touches the plastic, there is no insulation. So, there can be some freeze damage to the parts of the plant that touch the plastic. This can be prevented by placing stakes around a plant to hold the plastic up and off of the foliage. Heat can build up under clear plastic on a sunny day, so when clear or translucent plastic is used you must remove or vent it the next day if it is sunny and mild. It needn't be removed entirely if more freezes are imminent.

Greg Sevcik uses plastic bags to cover plants in the front yard of the home of he and wife Leslie Blanchard, Sunday afternoon, Feb. 14, 2021 to prepare for a hard freeze forecast for Monday night in the Baton Rouge area.

Fabric covers are heavier, especially blankets, comforters and quilts, and if the fabric gets wet from rain, the weight is even more of an issue. The weight of wet fabric can break plants, and wet fabric does not provide as much insulation as dry fabric. The weight can be dealt with by placing stakes under the cover to support the fabric up and off of the plants. Unlike plastic, fabric traps some air in the woven material, so leaves that touch a fabric cover are better insulated and not as likely to get freeze-damaged (unless the fabric is saturated with water). Since fabric covers limit the amount of light that the plant receives, they cannot be left in place for more than a few days and should be removed after the freezing episode is over.

The more layers of cover, the better the insulation provided. So, feel free to cover valuable or tender plants under more than one cover, especially during severe freezes. For instance, you could cover the plant with an old comforter and then a sheet of plastic (especially if rain is expected). Or fill in around and completely cover a small plant with mulch, such as leaves or pine straw, and then cover it with fabric, plastic, or both. Don't forget that whatever you choose to cover plants, the cover must extend all the way to the ground and be sealed with stones, bricks or soil. It is the warmth of the earth trapped under the cover that will help protect the plant, and this will not happen unless the cover extends to the ground.

Garden columnist Dan Gill answers readers' questions each week. To send a question, email Gill at gnogardening@agcenter.lsu.edu.

During extreme freezes in the low 20s or teens, putting strings of small outdoor incandescent Christmas lights under the cover can add considerably to the protection by providing additional heat. Make sure you use outdoor lights and extension cords.

I forgot to fertilize my plants last year. Is it too late to fertilize trees, shrubs and ground covers now? — Brenden Parks

Yes, it’s too late (or too early, depending on how you look at it) to fertilize the plants you mention. The most appropriate time to fertilize plants is just before or just as they start growing at the beginning of their growing season. This is particularly the case with most trees, shrubs and ground covers, because they tend to produce most of their growth early in their growing season (spring and early summer) and then grow very little thereafter.

You may also continue to fertilize plants during their growing season, especially if the plants continue to grow over a long season. The least appropriate time to fertilize is late in a plant’s growing season when the plant needs to be slowing down and getting ready for dormancy. Late fertilizer applications, after early September, can encourage hardy plants that should be getting ready for winter freezes to continue active growth, and this can make them more prone to cold injury.

When the winter solstice occurred Dec. 21, we experienced the day of the year with the shortest period of light and the longest period of darkness.

It is also not a good idea to fertilize plants when they are going dormant or have gone dormant, as the extra nutrients are not needed and generally go to waste. Trees, shrubs and ground covers are all dormant now, and would not benefit from fertilizer. So, only plants in active growth during the winter (such as cool-season bedding plants and vegetables) and perennials that grow during the winter (such as Louisiana irises) could be fertilized this time of the year.

COOL COLOR: Foxglove, delphinium and hollyhock are large, tall-growing, cool-season bedding plants that need to be planted early to put on a great display in spring. Get them planted this month or by early February for blooms beginning in April. These plants may be perennials in cooler zones, but they have a hard time surviving our summers. After flowering, they should be pulled up and composted.

BULBS WON'T WAIT: You must plant any spring-flowering bulbs you have been refrigerating now, or it will be too late. You cannot keep the bulbs and plant them next year. Don’t put this off any longer.

The fall and winter garden can provide lots of delicious vegetables. We begin to make its first plantings in August (fall crops of warm-season…

WEED ADVICE: Mild weather will encourage enthusiastic growth from cool-season weeds in the lawn. Because the lawn grass is dormant and mowing is not being done, the green weeds are really noticeable against the dormant turf. Do not reach for a bag of weed and feed — it is far too early to fertilize warm-season grasses. If you must control the weeds, use a broadleaf herbicide labeled for use on the type of grass you have following label directions carefully. Cool-season annual weeds will disappear when the weather turns hot and the lawn greens up. In the case of annual cool-season weeds, you can skip the herbicide and just mow the weeds down occasionally. It is more important to treat if you have problems with cool-season perennial weeds, such as dollarweed, clover and oxalis.

FERTILIZE IRISES: Louisiana irises may benefit from a light application of a general-purpose fertilizer now or in early February to encourage vigorous growth and abundant flowers. Control weeds and keep the planting mulched. Louisiana irises enjoy wet locations. They love the regular rainfall we receive this time of the year.

Dan Gill is a retired consumer horticulture specialist with the LSU AgCenter. He hosts the “Garden Show” on WWL-AM Saturdays at 9 a.m. Email gardening questions to gnogardening@agcenter.lsu.edu.

Many cool-season vegetables can be planted now and grown successfully in containers.

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