Over the weekend we had our first round of frost advisories and lows in the 30s. But, as long as you protected your plants, they probably made it through just fine.
While both a frost and freeze can be damaging to plants, it’s important to note that they are not the same thing. A freeze is more easily defined when temperature fall down below 32°F. While frost can also occur during a freeze, frost is about more than just temperature.
Typically, a frost can occur when the temperature falls below 36 degrees. Official temperature readings are taken 5 feet above the ground, so while the air temperature might be recorded in the mid 30s, the temperature at the surface could actually be lower. This is because cold air sinks, and especially on cold and dry nights, the difference from ground level to even just 5 feet above could be a couple of degrees, which is enough for the grass to be surrounded by 32 degree air.
But, unlike a hard freeze, there are other factors to consider too, like topography and wind. Topography can play a big role in frost because the lower the elevation, the more likely you are to have frost settle in when temperatures are above 32 degrees.
Wind can help to mix in warm air and keep it warmer on the ground. So, if you are hoping to keep your plants thriving, a breeze will usually be your friend.
So, when do we normally see our first freeze in Columbus? The average day for Columbus to officially report 32 degrees is October 27. But, record keeping goes all the way back to 1878, so there has been quite the range of dates that we have fallen to freezing for the first time. The earliest recording for a first freeze was September 21, but Columbus has made it as late as November 27 before falling to freezing.
The best way to protect your plants as lows start to dip into the 30s is to cover them with a blanket or towel. If you want to add an extra layer of isolation, you can put plastic on top of the towels. Make sure to remember to pull off these coverings in the morning though, otherwise condensation could build up around the plants, and then refreeze at night.