Temperatures in December 2022 were very damaging to many citrus in North Florida. It is necessary to give plants plenty of time into spring and summer to see if they will regrow and where that growth will occur. Learn how to care for your citrus that is suffering from cold temperature damage with Beth Bolles, UF IFAS Extension Escambia County.
We gardeners in the Panhandle have been spoiled by several very mild winters recently. However, it appears that this pattern will change, at least for a few days, beginning Thursday night. While forecasts vary depending upon your preferred media outlet, all agree that Calhoun County is going to experience several freezing nights (temperatures in the low 20’s to high teens for hours at a time). That’s plenty cold to kill many cold-sensitive plants, so here are a few tips to keep your treasured plants alive until warmer conditions arrive next week.
We don’t have many freeze events so take a little time this week to bring sensitive plants indoors and implement one or more of the above precautionary measures in your landscape! Don’t let a few hours of very cold weather set your plants back years! For more information about cold protection in the lawn and garden, contact your local UF/IFAS County Extension Office. Stay warm and Merry Christmas!
Freeze warning is a terrifying phrase for gardeners. Cold damages your plants and may even kill them outright. Understanding how plants freeze will help you create mitigating strategies for their preservation. Informing yourself as to how freeze damages plant tissues will allow you to fortify your garden.
Cold exposure happens in a couple of ways. Radiant heat loss occurs when one surface emits waves of heat into a colder surrounding environment. The surfaces of leaves and stems are not immune to this type of temperature transfer, nor is the soil in your garden beds. Frost may or may not form depending on moisture levels in the air, but cold damage will still be the result. The other main source of heat loss in gardens is through Advective freezes. These occur when cold air from the north moves south en masse resulting in colder temperatures and often increased winds. Mitigating this is a little tougher than radiant losses but not impossible
As with all things, planning is at the forefront. When designing your garden, cold hardiness should be considered. Certain plants naturally handle cold weather better than others. Utilizing native plants and those specified for your USDA hardiness zone will keep gardens alive in winter months. These tend to be acclimated for colder temperatures. Once the proper plants are selected and planted, ensure they are properly treated. Keeping your plants as healthy as possible is also critical in cold tolerance. Mulches and watering prior to a freeze event will reduce risk from radiant heat loss. The water absorbs warmth through the day and holds onto it more efficiently than dry soil would. Addition of a frost blanket will further reduce heat lost and ultimately the damage to your plants. A slightly more in-depth protection method comes from establishing microclimates in your yard. Use taller trees and windbreaks. Taller trees create a canopy that blocks heat loss to the atmosphere. Windbreaks keep the colder air away from your gardens and again prevent heat loss. None of these methods are fool proof but will help keep your gardens alive through the colder months. You may still experience damage from freezes. If this does happen, make sure your plants are watered to thaw any roots ensuring they function properly. Inspect stems by scraping a little tissue. Prune away any that shows black or brown tissue while keeping any which still looks green.
Freezes can be devastating to your gardens. A little knowledge can go a long way toward mitigating loss. For more information on cold protection, see this Ask IFAS document, or contact your local extension agent for additional information on this and any topic regarding your gardens and more.
For being in a place known as the Sunshine State, the Panhandle has been mighty cold and dreary to start 2022! With all the recent bitterly cold weather that’s rolled through our neck of the woods over the last month or so, you may be asking yourself “Is this just a typical Panhandle winter or has it been colder than normal and what is the impact of freezing weather on my fruit trees?” The answer might surprise you!
The easiest way to measure cold and its impact on plants is through a unit of measurement known as a “chill hour”. In its simplest iteration, a chill hour is an hour of time during which the thermometer dips below 45 degrees F. These “chilling hours” are vital to agriculture and our native ecosystems because many plants, especially those that produce fruit like pears, blueberries, peaches, and even citrus, require a certain amount of chill to enter dormancy and develop flower buds for the following spring. All fruit trees have a minimum chilling requirement to initiate flowering depending on variety and too few chilling hours equals poor to no fruit the following year. Too little cold can be just as harmful as too much!
Blueberry beginning to flower after receiving adequate chill hours. Photo courtesy of Daniel Leonard.
Now that we know about chilling hours, the question remains, is this a normal winter or has it been colder than normal? The answer is neither. Based on historical average data from the UF/IFAS weather station in Marianna (a central location in the Panhandle and a good proxy for your local temperatures), as cold as we’ve been in January and early February, we’re still lagging the historical average with respect to chilling hours, and therefore to total cold temperatures. As of February 6th, 512 chill hours had been recorded this winter. This seems like a lot until you check and see that we had 554 chill hours on the same day last year and the historic average is more than 750! Though January and February have indeed been cold this year, the chill hour graph indicates that over the last few years it’s taken longer into the calendar to achieve our first chill hour and that cold weather isn’t pushing as far into spring as it historically has.
There are many potential explanations for the warming trend in the Panhandle but regardless of your preferred theory, backyard fruit growers need to adapt to deal with the change in chill. The primary way to combat fewer chill hours is to evaluate your current fruiting plants and think about replacing high-chill varieties that no longer produce well with lower-chill varieties. If you know the variety you have, look up the number of chill hours that variety requires. If it’s an older variety that requires near the historical chill average or more, you may consider replacing it with a newer variety that requires fewer chilling hours. For example, the popular old blueberry variety ‘TifBlue’ requires 600-700 chilling hours. For most of the previous decade, we have either just barely or not reached that many chill hours, leading to a low fruit set. Replacing ‘TifBlue’ with a newer, lower chill variety like ‘Powderblue’ will probably increase your blueberry production. If you don’t know what variety of fruit tree or shrub you have, just observe the flowering period over the next spring or two. If it doesn’t flower at all or flowers sporadically and you don’t make a good fruit yield, a high chill requirement very likely could be to blame and replacing it could enhance production!
Though we’ve had an intensely cold start to 2022, if current trends continue, this wintry weather will most likely play out before we reach historic averages. That doesn’t mean you can’t grow plenty of backyard fruit, it just requires adapting to the times with lower chill varieties! To keep up with chill hour accumulation, visit http://agroclimate.org/tools/chill-hours-calculator and if you have any questions about fruiting plant variety selection, chilling hours and their effect on plants, or any other horticultural topic, contact your local UF/IFAS County Extension office! Stay warm and happy gardening!
February can be a confusing month for North Florida gardeners. Winter isn’t over. So, don’t let spring fever cause you to make some gardening mistakes. Let’s take a look at some dos and don’ts of February gardening.
Despite colder temperatures that we can experience this month, it’s still okay to plant trees and shrubs from containers. The roots are better protected in the ground and will quickly grow outward to establish as compared to being exposed to cold temperatures above ground, confined in a container. But be cautious about planting cold sensitive tropical plants too soon while freezing weather is likely. Bare-root trees and shrubs should be in the ground promptly. This includes bare-root nut and fruit trees, pine and hardwood tree seedlings and bare-root roses. Dormant season planting allows time for establishment before hot weather arrives.
February is a good time to transplant or move trees and shrubs that are in the wrong place. Consider moving plants that require pruning to force them to “fit” into small or confined spaces. Move them to an appropriate location where they can grow to full size. Then you can plant something new and appropriately sized for replacement. Of course, they need to be reasonable in size to move.
Bush rose plant correctly pruned. Photo credit: Matt Orwat
Late February is a good time to prune overgrown shrubs such as ligustrum and holly. These plants usually respond well to severe pruning, if necessary. But remember, they will eventually regrow to their larger size. Prune to shape and thin broadleaf evergreens and deciduous flowering trees such as oleander, crape myrtle and vitex. Avoid severely pruning narrow leaf evergreens such as junipers because they have few buds on old wood from which to form new growth. Mid-February is a good time to prune bush roses, removing dead or weak canes. Leave several healthy canes and cut these back to about eighteen inches. Delay doing much pruning on early spring flowering shrubs such as azalea until shortly after they flower. Pruning these plants now will remove present flower buds before they can open. Prune deciduous fruit trees such as peach, plum and apple. Now is also the time to prune ornamental grasses such as muhly grass.
If your lawn has a history of problems with summer annual weeds such as crabgrass, apply a preemergence herbicide. This should be done February 15 to March 1 when day temperatures reach 65° to 70°F for 4 or 5 consecutive days. A second application may be needed eight weeks later. Many people fertilize their lawns too early. Wait until mid-April to fertilize to prevent lawn injury and for the most efficient use of the fertilizer.
Use frost cloth to completely cover cold sensitive plants. Be sure to make complete contact with the ground and use heavy objects to keep the fabric secure. Photo by Jonathan Burns.
One major aspect that separates North Florida from South Florida is the discrepancies in air temperature. Although the differences are relatively small when comparing Florida with northern states, they can mean a world of difference in the plant world.
Even hardy cauliflower leaves can be damaged by cold winter nights in the Florida Panhandle. Photo by Molly Jameson.
In most of North Florida, our USDA plant hardiness zone is 8b, which means average minimum winter temperatures are between 15 and 20° Fahrenheit (F). We therefore can experience hard freezes, which happens when temperatures are below 28°F for over five hours. These types of conditions are capable of “burning” the leaves of even the toughest winter vegetables.
Fortunately for our winter gardens, average minimum winter temperatures are in the lower 40s, high enough not to damage winter garden crops. When we do have lows close to or below freezing (32°F), there is one very cost-effective method that can help keep crops and landscape plants protected. This is the use of a material called frost cloth.
Frost cloth can moderate air temperatures six to eight degrees. Photo by Turkey Hill Farm.
Frost cloth, which can be purchased at most plant nurseries, is a breathable polyester fabric that is light weight and heat retentive. When used correctly, it can moderate air temperatures about six to eight degrees. This is typically all that is needed to get us through our mild North Florida winters. It is also relatively inexpensive, and if cared for, the same cloth can be used for many winter seasons.
Large blankets or bedsheets can be used as frost cloth substitutes, but whether you are using actual frost cloth, or something pulled from the linen closet, it is very important to use it correctly to be effective. The cloth must touch the ground at all points, as it works by trapping heat that radiates from the soil. It also increases the humidity around the plant, aiding in temperature moderation.
“Lollipop” trees will allow the heat from the ground to escape, giving the tree no cold protection. Photo by Jonathan Burns.
For sensitive landscape plants and fruit trees, it can be more difficult to fully cover the plant with the frost cloth to trap the heat, but it is just as important. When driving around town on a cold night, I inevitably encounter a few “lollipop” trees. This is when the foliage of the tree is wrapped in frost cloth, but the cloth does not reach the ground, and is typically tied off at the upper trunk of the tree. All heat moving upward from the soil will go right around the cloth, giving the tree essentially no protection.
Wire or PVC hoops can be used to help secure frost cloth and keep the cloth from damaging sensitive plant stems and leaves. Bricks, sticks, soil, or garden staples should be used along the perimeter of the frost cloth to prevent nighttime gusts from blowing the cloth off your garden beds or landscape plants. In the morning, remove the cloth once air temperatures reach about 50 to 60°F.
To learn more about cold protection, check out the UF/IFAS EDIS publication, Cold Protection of Landscape Plants (https://edis.ifas.ufl.edu/publication/MG025).