We’ve finally had our first frost in some areas this week and perhaps some of us are seeing the effects on the landscape. Luckily it was just a light frost, but it’s time to make sure preparations are made to protect any cold-sensitive plants we’ve placed in the landscape.


Many tropical plants can start sustaining cold injury as temperatures drop below 50 degrees, so ideally these would be brought indoors during the cold, but for those that are planted outdoors we’ll discuss a few options to give that added protection.

While the temperatures that we just experienced, a high of 83 degrees followed by a low of 31 ust two days later, can be a real stressor even on many of the plants that can harden and acclimate over time to colder weather.

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While I won’t discuss the nitty gritty of a freeze, it’s good to understand a few concepts. There are two main types of cold events that are encountered, advective freezes and radiation frosts. An advective freeze is much more difficult to protect from than a radiation frost.

Advective freezes happen when moderate to strong winds blow in cold air, with no temperature inversion and relatively low humidity. Generally in this sort of event the temperatures will stay below freezing all day; the good news is these are less common in Florida.

Radiation frosts however are more common (this is what we just experienced), and these occur when heat radiates away from the ground, causing temperatures near the surface to drop at a higher rate than the air above. This is called a temperature inversion and it coincides with calm winds and clear skies. Sound familiar?

It’s fairly odd to think about but heat is radiated all of the time, and our plants radiate heat as well. When there is cloud cover, branches or some structure above a plant, they receive heat back as it is radiated away. But, when the skies are clear and with nothing to protect it, heat is radiated away without being returned resulting in, at times, significant temperature loss. These radiation frosts can be damaging to plants, but there are some simple frost protection practices available for this sort of event.

I’m only going to discuss some passive methods that are most suitable for homeowner application; active methods such as wind machines, heating systems and overhead sprinkler protection require a lot more financial and technical input to be successful without being wasteful. Applied incorrectly, the active methods can actually cause more damage than otherwise would have been expected. The simplest methods to reduce frost-damage for our sensitive plants outdoors include irrigation, mulching, placement and covers.

Irrigation is a very simple way to give a little extra protection. I’m not talking about leaving a sprinkler on throughout the freeze event — that’s an active method with a lot of risk. Simply irrigating the area well the day prior will give you a degree or two of protection. Water has a high heat retention; allowing all of that moisture to absorb heat throughout the day before a potential freeze event is a simple option for protection.

If night has already approached and then you find out it’s going to freeze, don’t irrigate! Since the sun has set the water won’t aid in the absorption of solar radiation and there will likely be a decrease in temperatures initially from evaporative cooling.

Having a well-irrigated planting also increases the humidity of the microclimate surrounding the plant, giving insulation to temperature changes when there is little wind.

Mulching can be a double-edged sword, while covering a plant or its trunk during a freeze will offer some insulation, it can also keep the soil from absorbing heat during the day, leaving you with less heat reserves as you enter a freeze. Thick weeds around a sensitive plant can also cause the same issue and increase risk as opposed to protecting from a freeze. Pulling mulch back during warmer weather can alleviate this issue. Adding extra to cover tender low-growing plants and removing the mulch once the freeze is over is a great, albeit labor-intensive option; just use a light much such as straw to avoid injuring the plants.

In terms of placement, it may be too late for this season, but when planting frost-sensitive plants they should be sited on the southern face of the house or some less sensitive evergreen windbreak to protect from cold northern winds. Proximity to structures or placement under a tree canopy will significantly reduce the likelihood of frost damage. Ever look outside and see frost everywhere on the lawn except underneath the trees? That’s the heat from the tree being radiated back down. Furthermore, plants placed under a canopy will likely go dormant sooner in the year as well.

This leads us right into the last option to be discussed, the use of covers. Simply placing a sheet, blanket or frost cloth over a sensitive plant allows that heat to be reflected back in addition to small amount of insulation; covers can result in temperature increase of 1-4 degrees, just enough for our generally mild frosts, Select the right option for your situation or combine several to created added protection.

Remember, you don’t have to know all of the answers, just the questions to ask. As always, scout regularly for best results. Have more horticulture questions? Feel free to reach out to the Master Gardener Volunteers at your local county extension office. Contact information for your county can be found at https://sfyl.ifas.ufl.edu/find-your-local-office/.
