Winter weather can be as chaotic as our calendar schedule during the holiday season. Quick changes in temperatures can send us scrambling to protect the three p’s – pipes, plants, and pets. South Louisianians may be experts preparing for a cat 5 hurricane but let the weatherman call for a bout of subfreezing temperatures and a hint of flurries and we go to DEFCON 1.
While most people know how to protect pipes and pets, plants can be a mystery. Should they be covered? Driving around on cold winter mornings, I have seen plants of all kinds covered. I’ve seen coverings on many plants that do not need protection.
Thanks to our latitude and proximity to the Gulf, we fall on the border of temperate and subtropical climates. This allows us to grow many plants from both climate regions. However, it’s typically only subtropical plants that will need freeze protection.
When preparing for an Arctic blast, some people take the blanket approach – if it’s planted in the ground throw a blanket over it. Others are more strategic with what they cover, and this is the way it should be. Not every plant needs a warm blanket, if in fact, many thrive in the cold and welcome its chilling hours.
Chilling hours may be a term you’re familiar with. To understand chilling hours, we need to look at dormancy and specifically, which plants require it. As the mercury slides below 50 F for extended periods and daylength decrease, temperate, deciduous fruiting plants will enter dormancy – a period of rest. Dormancy is divided into three main stages – acclimation, endo- and eco-dormancy, and deacclimation.
Acclimation prepares plants for freezing weather. This mainly occurs during October and November when temperatures cool, growth stops, and all fruit has ripened. If temperatures drop suddenly before the acclimation period is met, plants can sustain cold weather injury.
The second stage of dormancy is divided into two parts, endo and eco. Endo-dormancy is the chilling hour accumulation period. Temperate fruiting plants have internal signals controlled by hormones that respond to a certain length of time when temperatures are between 32 F and 45 F. This varies by variety. Bud break and flowering will not occur until the requirement is met. Once this occurs, plants enter eco-dormancy which is dormancy regulated by cold temperatures. Once temperatures warm, plants transition to the final stage.
Deacclimation is the final stage and the process of breaking dormancy. This period readjusts plants to warmer weather and starts when temperatures rise above 40 F. Plants start accruing growing-degree days like chilling hours lead to bud break when enough heat is accumulated. This can occur early if we have a warm winter.
Covering temperate plants that need chilling hours during cold weather can hinder the natural dormancy process. Temperate fruit crops such as apples, pears, peaches, plums, nectarines, blueberries, blackberries, and even figs all have varying chilling hour requirements. The requirements vary depending on the variety as well. Due to our mild winter weather, we select for low chilling hour requirements, typically between 300-600 hours for Livingston Parish.
When chilling hour requirements are not met, the plants biological clock goes cuckoo. Buds may remain dormant too long, blooming is erratic or fails to occur, and fruit set is either skipped, delayed, or sparse. This is why it is important to match the right fruit variety to our area and allow it to experience normal winter dormancy unhindered.
Of course, to every rule there are exceptions. Temperate fruit crops are susceptible to cold damage to flower buds and fruit. When warm, late winter weather forces early bloom development and fruit set, these will need to be protected if late season frost occurs.
Save yourself time and effort this winter and leave the cold weather survivors and thrivers to mother nature. These hardy plants will do just fine.
The picture accompanying this article is of one of my LSU Purple fig trees during the cold and snow back in January. It did just fine with no protection.
