WEATHER GUIDE: COLD WEATHER TIPS

Crop with Frost

When temperature approaches freezing in Southwest Florida special precautions need to be taken to prevent permanent injury to our cold sensitive plantings.

What to protect: All tropical plants, whether planted in the ground or pots will need protection when the temperature is expected to drop below 35º F. Hibiscus, Crotons, Bouganvillas, and Ixora along with Coconut Palms, Areca Palms, Royal Palms and Adonidia Palms (Christmas Palms) to name a few, must be protected. Tropical fruit trees like Mangos and Carambolas will also need attention. Citrus very rarely require protection from cold unless the temperature is expected to drop below 29º F for more than 3 or 4 hours.

How to protect your plants: The first thing to do before cold weather is expected is to make sure that your plants are well watered. Give all your plants a good drink during the day. Be sure to water early enough in the day to ensure the plants are dry going into the dark.

Containerized plants are best moved into a covered area like a garage, carport or patio. If the structure is open to the air choose a location that is open to the south.

For plants outside, it is best to cover the plants with a cloth cover. Old sheets and blankets are best, but contrary to what some may say, plastic and other synthetic material covers will work too. If you can create a “structure” to keep the covering material off the plants, that would be ideal. Any portion of the plant that comes in contact with the covering material will likely get injured because the cold will transfer through the covering materials to the foliage. So keep as much of the covering material as possible off the plants foliage.

This covering process is most effective in protecting your plants against injury from frost. Frost will occur only if there is no cloud cover AND there is NO wind. If either of these conditions is not met there won’t be any frost. I have seen frost occur on plants in our area at temperature as high as 36º F. If the temperature is expected to drop below 32º F your covering alone may not be sufficient to protect your plants.

When the temperature drops below freezing, especially if it drops into the 20’s, you will need to add a heat source to your covered plants. In many cases the easiest way to get heat to your plants is by adding a lighted floodlight or two under the covered plants. Christmas tree lights will also work if you add enough. It is also advisable to make sure your covering materials go all the way to the ground, so that any heat coming from the ground will be trapped inside the cover.

Larger plants and palms that can’t be easily covered are very difficult to protect. For palms if you can wrap the top of the trunk at the bud area this may help protect the bud (growing point) from cold injury. Because the palms only have one growing point, if the bud dies or is damaged the palm will not recover. Protecting the foliage of a palm is not as important as protecting the bud. Infrared type outdoor space heaters can also direct heat toward the bud area of a taller palm. As a last resort, if you can create a heat source close to the trunk this will create an updraft around the trunk and bud of the tree that may prevent frost from settling on the bud area of the palm.

Larger shrubs can be protected by “banking” the base of the plant with dirt. Because the soil in our area doesn’t freeze, pilling up dirt around the base of the plant will stop the cold from killing the portion of the plant that is banked with dirt. This is an especially effective method to protect grafted plants like Hibiscus, Gardenias and young Citrus. If the graft is protected, and the plant is severely injured, the plant will regrow back from the grafted portion of the plant. However, if the graft area is killed the plant that regrows from the rootstock will not be the same desirable species as before the cold.

What about water to protect my plants? You will no doubt see TV coverage of farmers and nurserymen protecting their plants from cold damage with water. This is NOT a practical method of cold protection for homeowners. In order for water to work as a protective blanket for your plants, you must continuously apply water to the plants. The idea is that as long as you are applying water to the foliage of the plants the temperature will stay at 32.1º F, preventing the plant from freezing. The scientists will say that by definition when a gram of water freezes it gives up 1 kilocalorie of heat. However, if the water stops, or slows down plants covered in ice will actually super cool to below the air temperature. Home irrigation systems just don’t provide enough water fast enough to do any good.

What about after the cold? In the morning, once the temperature gets above 38º F you should uncover your plants. If your covered plants are in the sun, the cover can quickly trap in excess heat causing more damage to your plants. “Banked” plants can remain covered for several months until the danger of frost is past.

If your plants sustain cold damage it is very important to reduce your watering right away. Excess water can cause root rot problems, so we recommend shutting off your sprinkler system until plants begin to show signs of regrowth or undamaged foliage begins to wilt.

When can I trim my damaged plants? Wait, Wait, Wait!!! It is best for you to wait until your plants begin to show signs of new growth before doing any trimming. There are several reasons why:

Over the years I have seen numerous situations where plant tissue I was sure was dead has miraculously grown. If you trim too early you are very likely cutting off portions of the plant that will regrow, if you give it a chance.

Until the chance of frost is completely past (approximately mid-February to mid-March in our area), the damaged foliage will provide some additional protection from future frost injury.

Pruning too early may stimulate new growth that can be injured again. Your plants may not be strong enough to come back twice.

We hope this information will be helpful in protecting your plants from cold injury.

COLD WEATHER TURF DAMAGE

Injury to warm-season turfgrasses often occurs when temperatures drop below 20°F (-6.7°C). In general, major winter injury to turfgrass is caused by the following:
• Tissue desiccation
• Direct low temperature kill
• Diseases
• Traffic effects

For example, damage from the 1989-90 freeze can probably be attributed to poor cultural practices which weakened turf and made it more susceptible to injury or death from low temperatures. Subsequent damage may also have resulted from effects of traffic on frozen turf.

Most warm-season grasses have very poor cold tolerance ratings when compared to cool-season grasses. Due to lower fall temperatures and reduced day length, warm-season grasses enter a state of dormancy, evidenced by brown, dead shoot tissue. This death of shoot tissue or lack of growth does not generally indicate that the grass is not going to recover; instead, this is a natural state and provides protection for the grass when faced with cold temperatures.

In cases of severe freezing temperatures, some grasses may suffer irreversible damage, and use of these grasses should be limited to warmer climates. For instance, St. Augustine grass, which generally exhibits poor cold tolerance, is not used as extensively in north Florida as other grasses, and is used less as you progress into northern Georgia.

Cultural factors that tend to promote cold injury include: poor drainage (soil compaction), excessive thatch, reduced lighting, excessive fall nitrogen fertilization, and a close mowing height. The weather pattern preceding a severe and sudden cold wave also influences a turf's low temperature tolerance.

In general, if turf has had several frosts prior to a drastic temperature drop, it has been better “conditioned” to survive. The 1989-90 cold snap in much of north and central Florida was preceded by three to five frosts. These helped increase carbohydrates and proteins in plants that enabled crown tissue to withstand cold temperatures without severe membrane disruption. The freezes that occurred in the early 1980s did not have these preconditioning periods, resulting in severe damage. In this case, grasses were still green, and protective crown tissue was succulent and therefore susceptible to cold temperatures.

Shaded areas may suffer more intense cold damage. Shade (low light intensity) prevents normal daytime soil warming. Shade also reduces the plant's ability to produce carbohydrates needed for increased cold tolerance.

Traffic (foot or vehicular) may further increase injury to cold damaged turf. Traffic should not be allowed on frozen turf until the soil and plants have completely thawed.

For more information go to: http://edis.ifas.ufl.edu/LH067
Low Temperature Damage to Turf. L.E. Trenholm. Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published: May 1991. Revised:

TURF & THE COLD

Symptoms of direct low temperature damage include leaves that initially appear wilted, take on a water-soaked look, tend to mat over the soil, and often emitting a distinct putrid odor. Areas hardest hit are usually poorly drained ones such as soil depressions. If you suspect your grass has experienced cold damage, take several 4” to 5” diameter plugs and place them in a greenhouse or warm windowsill. Observe these for 30 days or until growth resumes. If regrowth occurs, little damage is assumed. If regrowth is absent, some degree of damage was sustained.

In St. Augustine grasses, 'Raleigh,' 'Bitterblue,' 'Seville,' and 'Jade' generally exhibit the best cold tolerance, while 'Floratam,' 'Floralawn,' and 'Floratine' are more susceptible to cold temperatures.

Regardless of turfgrass species selected, the following management practices can help minimize cold temperature damage.


Recently planted grasses can expect to be more severely damaged by cold. Ooverall stress tolerance is reduced in grasses undergoing establishment. In south Florida care should be taken to protect immature turf from occasional cold temperatures.
Fertility can also influence cold tolerance. Late season (after mid October in the central and southern regions) application of nitrogen will promote shoot growth in the fall, when the grass growth and metabolism are slowing down. This will deplete carbohydrate reserves and will produce new, tender shoot growth that is less able to tolerate cold. Therefore, late-season application of nitrogen is not recommended.
Potassium fertility in the fall has been shown to enhance cold tolerance and promote earlier spring green-up of grass. Application of potassium at the rate of ½ to 1 lb. per 1000 square feet is recommended for the last fertilization of the year.
Shade can increase cold damage because shade does not become as warm as areas in full sun. Injury in these areas may be more severe. Compacted soils also remain cooler than well-drained areas, which increases the probability of cold temperature damage.
Increasing mowing height can reduce cold injury, promote deeper rooting, allow for production and storage of more carbohydrates late in the summer, and can create a warmer micro-environment due to extra canopy cover.
Because cold damage may initially resemble drought stress, people sometimes feels that additional water may be needed. Overall, correct irrigation practices as described throughout the Florida Lawn Handbook can alleviate many stresses faced by turf, but as the grass goes into dormancy, water needs are reduced.
Unless your turfgrass has been subjected to unusually cold or freezing temperatures for long periods, or your management practices have augmented the effects of the temperatures, your grass should begin to green-up as temperatures and day lengths increase in the spring. At this time, recommended fertility, irrigation, and mowing practices should be resumed for best health of your lawn all season.
For more information go to: http://edis.ifas.ufl.edu/LH067
Low Temperature Damage to Turf. L.E. Trenholm. Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published: May 1991. Revised: May 2000.