2018 started with a bang, reminding us that winter has definitely arrived. Earlier this week, most of us experienced freezing temperatures accompanied by high winds. Some lost power while others witnessed a few snow flurries. Now the roller coaster begins as we creep back into the 60s and low 70s, typical of northeast Florida winters.

 

A hard freeze has benefits in that it kills some persistent warm-weather weeds, reduces the number of pest problems and provides chilling needs for some of our temperate fruit. But along with the pluses, winter freezes play havoc with some of our landscape plants. Plants that are most at risk are warm season annuals and semi-tropical plants that are gaining in popularity due to previous mild winters. Norfolk Island pine, bougainvillea, croton and schefflera are just a few examples of semi-tropical plants that are showing up more frequently but are not cold-hardy.

This is only the beginning of winter and if this is a sign of things to come, we may be in for a colder winter than normal. To help deal with the cold, here is a list of some of the more common plant questions that we get at the Extension Office prior to and after a freeze.

What should I do before the freeze?

Healthy plants will have a better chance of making it through the winter unscathed. Diseased plants and lawns, plants with nutritional deficiencies, plants pruned prematurely in the fall or lawns that are mowed too short will be more susceptible to cold injury. Although it’s a little late now, the bottom line is make sure plants are healthy going into winter.

If the soil is dry and the cold front is not preceded by rainfall, water the landscape before the freeze. Watering 48 hours before the freeze will elevate the night temperatures by 2 degrees. Don’t overdo it. A soggy soil is not healthy for plant roots and will create root diseases down the line.

Cover sensitive plants with blankets or leaf mulch, bank sand around citrus trunks, and bring sensitive houseplants inside. Make sure to check for hitchhikers in container plants. Many different kinds of insects, snakes and lizards are potential occupants and most of us would prefer to keep the critters outside. If there’s no room inside, place container plants in a protected area (east or south side of a structure or under a tree), cluster them together, and cover with leaf mulch. Another option instead of banking sand around the trunks of cold sensitive trees is to wrap trunks and lower limbs with newspapers, blankets, foam rubber or insulation. If using newspaper for wrapping, the thickness should consist of several sections for insulation. It is best to unwrap after the freeze to reduce the moisture on the trunks and to allow sunlight to heat up the wood.

If temperatures drop into the teens, the best protection is to build a mini-greenhouse around prized plants. Build a wood or PVC frame and cover with fabric materials or row cover frost blanket. Fabric materials work better than plastic. Plastic conducts cold so if leaves touch the plastic, the damage will be intensified.

If you can’t find row covers at local garden centers, check gardening catalogues and the web. The time to purchase materials is before the freeze as they will quickly sell out when a freeze is imminent. They are relatively inexpensive and can be reused from year to year.

To help get a prized semi-tropical plant through a freeze, you might consider adding a heat source under the mini-greenhouse or covered area. The best heat source is an incandescent bulb placed at or near ground level because heat rises. The newer fluorescent bulbs are not effective as they don’t generate a lot of heat. A 40-watt bulb will be OK for lower growing plants, whereas a 75-watt bulb or more will be needed for larger plants.

Should I run my sprinkler system during the freeze?

Do not run irrigation systems during the freeze. Although this is done by commercial producers, it is unlikely that this practice will be beneficial in the landscape. A constant supply of water must be applied and the end result may be root rot disease or limb breakage instead of cold damage. It’s more important to water before the freeze to help heat up the soil.

Should I harvest my citrus?

Citrus should be harvested if temperatures fall below 28 degrees for four or more consecutive hours. If fruit are not ripe, leave them on the tree because they will not ripen once picked. If fruit are frozen, they can still be harvested for juice if used within a few days of the freeze. Large and thick-skinned fruit are more cold tolerant than small, thin-skinned fruit. Fruit most susceptible to freezes are those on the top and outside of the tree. If the freeze is accompanied by strong NW winds, fruit facing that direction could suffer damage whereas those on the SE side may be untouched. Severely frozen fruit typically fall to the ground within a few days due to damage to the stem and fruit. Fruit lightly frozen and immature will usually remain on the tree and can be eaten.

What should I do after the freeze?

Check water needs of plants after the freeze. Apply water to plants if they appear to be dried out or if there were high winds associated with the freeze.

Delay pruning of damaged plants until new growth appears in the spring. If the plant (gingers, firespike, etc.) reliably comes back from the root system, go ahead and remove the damaged tops. These plants are usually pruned to the ground following a freeze.

A lawn that turns brown after a freeze indicates it has entered dormancy. Don’t be alarmed — this is normal for Florida lawns. As warm weather returns in the spring, new growth will hopefully emerge. In the meantime, once it enters dormancy, it no longer needs mowing. Irrigation may still be needed in the absence of rainfall but once every other week should be adequate. Don’t try to force the lawn by applying nitrogen fertilizers and don’t scalp it to remove the brown. Wait and let nature take its course to see if the lawn greens up in March or April. At that time, damaged areas will be obvious and repairs can be made.

For more information on freeze protection: edis.ifas.ufl.edu/mg025.

Terry Brite DelValle is a horticulture extension agent with the Duval County Extension Service and the University of Florida/IFAS.