(News article for February 17, 2021; edited)
As I write this, we’ve just experienced one of the coldest nights we’ve had within the past few years. The forecast for Tangipahoa and Washington Parishes includes several more nights in the mid-20s, followed by warmer temperatures.
By the time you read this, there will likely be questions about how to deal with cold-damaged plants.
Parts of herbaceous (non-woody) plants that are brown and obviously dead can be cut back soon, although there doesn't generally need to be a rush to do so.
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 during the summer. Parts of the plant that have injured shoots may end up putting out new growth. Likewise, a cold-injured tree 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 injury on citrus. At that time, you can remove dead wood.
Also remember to remove rootstock growth from below the graft union as citrus plants recover.
If you haven’t already fertilized citrus plants this winter and it appears that you have cold injury, reduce the amount of fertilizer in proportion to the part of the tree that appears damaged. For example, if you have a 10 year old tree and would therefore normally use 10 pounds of 13-13-13 around the tree, but about half the tree appears damaged, you can reduce the amount of fertilizer to 5 pounds of 13-13-13.
As root systems of cold-damage citrus trees have likely been injured as well, you can 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.
We’ll likely see cold injury on palm species that are marginally hardy for this area. 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 determine whether or not a palm is dead.
As you buy new plants, remember to select ones that are cold hardy to USDA Hardiness Zone 8B, for most of Tangipahoa and Washington Parishes, or to 9A, for the very southern part of Tangipahoa Parish (roughly the area south of I-12). Plants hardy to Zone 8B should be able to withstand temperatures as cold as 15 to 20 degrees F, while those hardy to 9A should be able to tolerate temperatures down to 20 to 25 degrees F.
Let me know if you have questions.
Contact Mary Helen Ferguson.