Landscape Lessons from Recent Freezes

Landscape Lessons from Recent Freezes

There are important landscape lessons to learn from recent, early and widespread freezes.

First, know the average climate for the region you live in here in Florida. The work has already been done for you with the USDA Plant Hardiness Zone Map. Here is a link for the map: https://planthardiness.ars.usda.gov. Find your zone on the map. Note that Northwest Florida includes zones 8a, 8b and 9a.

The newest map, with interactive features, was updated in 2012.

This map is based on the average annual minimum winter temperature and is divided into 10°F zones. It can help you determine which plants are most likely to thrive in your zone. There are areas bordering Alabama, located in the extreme northern portions of Escambia, Santa Rosa, Okaloosa, Walton and Holmes Counties, that are in Zone 8a, with an average annual extreme minimum temperature of 10 to 15 degrees F. Most of these counties fall within zone 8b, with an average annual extreme minimum temperature of 15 to 20 degrees F. The extreme southern portions of these same counties (bordering the Gulf) are in Zone 9a with an average annual extreme minimum temperature of 20 to 25 degrees F. As you go south in Florida, you move into Zones 9b, 10a, 10b, and 11a. Zone 10b has an average annual extreme minimum temperature of 35 to 40 degrees F. Zone 11a; which includes a small portion of West Palm Beach and Fort Lauderdale, most of Miami and all of the Florida Keys; has an average annual extreme minimum temperature of 40 to 45 degrees F.

Most of the Panhandle is in USDA Hardiness zone 8b.

It seems that some people move to extreme north Florida and think they are in extreme south Florida. They move barely below Alabama or Georgia and want to plant the palms, citrus and tropical plants that thrive in extreme south Florida. If you live in Zone 9a, perhaps you might get by with growing a few plants that are well suited for 9b. But it is wise to mostly grow plants that are known to flourish in the Plant Hardiness Zone where you live. 

Secondly, follow principle one, which is Right Plant, Right Place, as explained in the UF/IFAS Extension Florida-Friendly Landscape™ (FFL) Program. Following this principle results in developing a healthy, low-maintenance landscape by using Florida-Friendly plants that match your site’s soil, light, water and climatic conditions and that require limited supplemental irrigation, potentially less fertilizer and fewer pesticides.

More information on the FFL Program is available through this UF/IFAS Extension link (https://ffl.ifas.ufl.edu) or from the Extension Office in your County.

Using these tools may be a great goal for 2023 as we replace cold-injured plants.

Getting Your Plants Through a Freeze

Getting Your Plants Through a Freeze

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.

Covering plants to protect from frost, cold snap, blanketing, potted plants, horticulture. UF/IFAS Photo: Sally Lanigan.
  • Bring cold-sensitive potted plants inside.  You can’t dig up your citrus trees and bring them in the living room but bringing cold-sensitive potted plants inside for a couple of nights is a fail-proof freeze protection method.
  • Water outside plants the day before extreme cold hits.  It’s natural, even good, for many tender plants (perennials, bulbs, etc.) to “die” back in cold weather.  This encourages dormancy and reduces pest/disease populations.  However, this week could get cold enough to kill “tops” of sensitive plants AND freeze root systems.  To help prevent this, water the day before a freeze as moist soil loses heat less rapidly than dry. A few degrees can make all the difference!
  • Apply mulch around the base of plants.  Mulch helps insulate the soil and reduces radiant heat losses.  For plants with a graft – like most citrus, pile mulch up around the grafted area.  If the top of the plant dies back, at least it will be able to recover from above the graft (the desirable part of a grafted plant). 
  • Cover citrus and other plants that recover slowly from cold damage.  Draping a non-plastic cloth or blanket mostly helps keep frost off and freezing wind off plants but can also insulate from freezing temperatures if it covers the entire plant to the ground.  It’s better than nothing.
  • Build a “greenhouse” around plants.   You can create a simple greenhouse structure of wooden stakes, pipe, or posts and cover with plastic (making sure the plastic doesn’t touch leaf or stem tissue).  Be sure to get this structure up while the sun is still shining before the freeze event to capture as much solar heat as possible.  For even better results, install a lightbulb, non-LED Christmas lights, or some other heat source inside the plastic structure.
  • Last ditch method – turn on the sprinkler.   Continuouslyrunning a sprinkler over sensitive plants can help protect them.  By running water, you “insulate” the plant to the water’s temperature (above 32 F).  This method requires that the sprinkler begin running before the thermometer drops below 32 degrees and must continue uninterrupted until after the freeze event is over.  If you stop before the freeze is over, the water left on the plant will freeze to whatever temperature the air is, injuring or killing the plant.

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!

The Ultimate Poinsettia Care Guide

The Ultimate Poinsettia Care Guide

The flower of the Christmas season is the poinsettia, a tropical plant from Mexico that changes its leaf color when the daylength changes.  Poinsettias were originally noticed for their bright red color and are now available in many colors, shapes and sizes, thanks to decades of work by plant breeders.  As much as we love them, caring for poinsettias during and after the holiday can be a challenge.  Here are a few tips to extend the bloom for a longer period and encourage it to grow for the months to come!

Photo credit: Tyler Jones.
  • Provide plenty of sunlight.  A sunny window facing south is ideal.  Be careful to not let the leaves touch the glass. Keep temperatures around 55-60F at night and 65-70F during the day.
  • Keep soil slightly moist on the surface.  Wait until the surface feels dry before watering, then add just enough to soak in.  If water collects below the pot, pour it out.  Those decorative wrappers make it hard to tell, so be sure to check.  However, don’t wait for wilting before watering as that is too dry.  Both overwatering and underwatering can lead to wilting and excessive leaf drop.  Check the soil each day.
  • Don’t fertilize while “blooming”.  While the colored parts of poinsettias are actually modified leaves called bracts and the true flowers are the tiny yellow centers, we often refer to the entire non-green portion as a bloom.  The plant can maintain its nutritional needs throughout the flowering time without additional fertilizer.
  • In the spring, cut the plant back, fertilize and move outside.  Remember, poinsettias require temperatures to always stay above 60F.  If we receive any cool nights, bring it in for the night.  Let the rootball become quite dry throughout April.  You may have to move it under a cover if the April showers are occurring every few days.

If you want to try your luck at re-blooming, re-pot it in a slightly larger container and cut it back to about 4” high in mid-May.  Keep it in nearly full sun.  A little shading in the heat of the day is helpful.  Water consistently and fertilize every two weeks with a water-soluble, complete fertilizer.  As it grows, you will need to pinch the plant back every six weeks or so until October, I usually remove about half of the stem that has grown out.  To get coloration in time for Christmas, find something dark to cover the plant or move it to a dark location each day.  The poinsettia must be in complete darkness from 5 p.m. to 8 a.m. until the leaves start to turn color, usually 10 weeks. That means moving or covering and uncovering at the same time every day.  Any deviation will delay the color change.  Once you see a complete set of leaves coloring, the plant can be exposed to regular daylengths.  If this sounds like too much work, spent poinsettias do make good compost and garden centers will be happy to sell you a new one!

Remember, poinsettia sap does contain a latex-like chemical that can cause allergic reactions.  Small animals, young children, and adults with allergies should not handle poinsettias.  If eaten, get medical attention immediately.

Chill Hours:  What Are They and Why Do They Matter?

Chill Hours: What Are They and Why Do They Matter?

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!

 

Winter Care of Landscape Plants

Winter Care of Landscape Plants

January and February are typically the coldest months in Florida. Low temperatures can damage even the more cold-hardy plants. However, there are measures that can be done to help cold-damaged plants recover.

After a frost or freeze, see if your plants are dry. Even injured plants need water. Plants can be greatly damaged if the temperature drops suddenly, as they have no time to acclimate to the freezing temperatures.  These freezing temps cause ice crystals to form in plants cells.  These crystals expand, rupturing the cell walls and preventing the plant from maintaining shape.  If severe, this can certainly kill tender plants.  On more cold hardy plants, damaged foliage will appear wilted and curled down.  In a few hours or days, it will darken and turn black.  Flowers, buds, and new growth often dieback under freezing temps.

After freezing temperatures occur, it’s important to remove damaged leaves and flowers as soon as they turn brown or black.  This will help prevent diseases from occurring.  Pruning should be postponed until cold temperatures are no longer expected and new growth begins to appear on the plant.  This practice ensures live wood, which appears dead from losing its leaves, is not mistakenly removed from the plant.  Cold damaged wood can be detected by examining the cambium layer (under the bark) of the plant.  If it has black or brown discoloration, it is damaged and should be pruned back behind these points.  Plants should be fertilized in the spring, to encourage new growth.

Cold damage to plant

Cold damage. Photo Credit: University of Florida/IFAS

What about proactive care? You can accomplish this by moving potted plants indoors and covering tender landscape plants with a protective covering.  Protective covering can include old bed sheet, pieces of material or fabric, and cardboard boxes.  Be careful not to let the protective covering touch the plants.  The surface of the covering will become as cold as the air temperatures and may damage any tender leaves it encounters.  Also, don’t forget to remove the covering the next day when temperature raises this is important so the plants do not “bake” in the warmer temperatures.  Plants placed near the house, lights, or other structures, which shelter them from wind, will be more protected than those fully exposed to the cold air.

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.

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.

For more information on freeze damage plants contact your local county extension office.

Supporting information for this article can be found in the UF/IFAS Extension EDIS publication: “Cold Protection of Landscape Plants”, by Sydney Park Brown: https://edis.ifas.ufl.edu/publication/mg025

Protect Your Winter Garden and Landscape Plants with Frost Cloth

Protect Your Winter Garden and Landscape Plants with Frost Cloth

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.

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.

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 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.

“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).