LSU AgCenter's Weekly Message

What to Do After the Cold Weather, and Tips for Future Cold Events

As I prepare this, we’re getting ready for the coldest temperatures we’ve had so far this winter. It doesn’t look like they’ll get close to the low teens or single digits that we had last year, but the anticipated low 20s are still cold by our standards.

Parts of herbaceous (non-woody) plants that are brown and obviously dead can be cut back soon, though there doesn't need to be a rush to do so, and leaving some of the plant tissue may help protect them from cold weather later in the season. Research has found that pollinators and other beneficial insects often live in perennials’ dead stems that have been allowed to remain in place for the following growing season. Based on this, it’s been suggested to leave the first 1 to 2 feet of dead stems for insect habitat.

For woody plants and palms, waiting is advised.

On citrus trees, you may not be able to tell the full extent of cold damage until sometime in the summer. Branches or trunks that look damaged may end up putting out new growth. At the same time, cold-damaged trees may put out flushes of new growth that later collapse. Waiting until July or August, after the second annual flush of growth has occurred, gives you more time to see the full extent of cold damage. At that time, you can remove dead wood.

Also remember to remove rootstock growth from below the graft union as citrus plants recover. Most rootstocks have trifoliate leaves (leaves with three leaflets), so their foliage looks different than that originating from the scion (top part of the grafted tree).

When the time comes to fertilize citrus trees in late winter or early spring, if it appears that you have cold injury, you can reduce the amount of fertilizer in proportion to the part of the tree that appears damaged and, instead of applying it all at once, divide the total amount of fertilizer up into several smaller applications. Be sure not to fertilize after the end of June, though, since late fertilizer application can predispose citrus trees to cold damage the following winter.

On cold damaged palms, it’s recommended to let brown leaves remain until no further hard freezes are likely to occur. Survival of palms depends on survival of the growing tip (meristem) at the top of the plant. Dead or injured leaves can still help protect the growing tip from remaining cold events. Since palms do not put out new growth until later than many other plants, wait until July to make the call about whether or not a palm is dead.

When you buy new plants, remember to choose ones that are cold hardy in your area, if you don’t want to have to protect them. Since the 2023 update to the USDA Hardiness Zone map, most of Tangipahoa and Washington Parishes have been in Zone 9A. There are still some patches of Zone 8B in northern Tangipahoa Parish and western and north-central Washington Parish.

Hardiness Zone 9A indicates average minimum temperatures of 20 to 25 degrees F. Since hardiness zones are based on average minimums, we occasionally experience temperatures lower than that range, as we did last year. If you want to play it safe, you can continue to select plants that are hardy enough for Zone 8B.

When a freeze is expected, make sure that plants have adequate water. Moist soil retains more heat than dry soil. Also, if the water around a plant’s roots freezes, the plant will not be able to take it up while it’s frozen, so it needs to have sufficient water beforehand.

Mulch is desirable in many situations and can help protect plant roots from cold temperatures, if the roots are the part of concern. However, with citrus trees, the rootstock is very cold hardy. It’s the scion that’s more cold sensitive. Bare soil heats up more during the day than soil that is covered with mulch and therefore can provide more heat at night. For marginally hardy citrus trees, one thing you can do to provide a small amount of cold protection is to remove weeds, grass, and mulch under the plant. For this to be useful, the soil needs time to heat up, so don’t wait until late afternoon of the day before the freeze to do it.

When temperatures are expected to get colder than a particular plant can withstand, covering plants is sometimes an option. The cover should extend to the ground. A variety of materials can be used, but try to avoid having direct contact between the plant and the cover, especially if it’s plastic. Also, if you use a plastic cover, make sure to take it off or vent it during the day so that the plant won’t get too hot.

For additional cold protection, an incandescent light bulb can be placed under the cover. Make sure the light won’t get wet, and avoid direct contact between the light and either the tree or the cover.

For citrus in particular, a final thing you can do is to protect the trunk from the base to some point above the graft union with an insulating material. If part of the scion survives, the tree is likely to be able to regrow from it.

Let me know if you have questions.

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Dr. Mary Helen Ferguson is an Extension Agent with the LSU AgCenter, with horticulture responsibilities in Washington and Tangipahoa Parishes. Contact Mary Helen at mhferguson@agcenter.lsu.edu or 985-277-1850 (Hammond) or 985-839-7855 (Franklinton).