Cold Weather Tips: Frost

When should you expect frost?

Spring snowdrop flowers in snow

Frost is formed from high moisture content in the air with temperatures near to below freezing. Although frost is most likely to form in a moist environment with temperatures around freezing, you can actually see frost at temperatures up to 36º F because temperature sensors are 6 feet off the ground. Ground surface temperatures are often colder than actual air temperature. You’ve probably noticed that on overcast nights cloud cover acts like a blanket over the lower atmosphere, stopping the warm air from escaping. However, with clear skies and calm winds radiant heat can rise up from the Earth to the upper layers of the atmosphere. Temperatures also can vary depending on your location. This means on your property you may see different temperatures on either side of your house, under trees, on south or north facing slopes, in wind-protected areas, or in low-lying spots. Now that you know about when frost can occur, you need to know how it will affect your plants…

How do you protect your crops?

As those in the agricultural business know, the amount of time fruit spends at low temperature is decisive. For example, mandarin fruit can withstand a brief drop in temperature to 24º F, but several sustained hours at 26º F will damage it. It’s not just the fruit; leaves and green wood are cold sensitive too. Seasoned farmers know to prepare for a frost by entirely covering the plants or even covering a whole row of small trees and hanging a heat source in the middle—such as Christmas tree lights!

What should you do if a hard frost is predicted?

weather thermometer freezingWe know that fruit can easily be damaged by a surprise frost. Since the best place to store ripe citrus is on the tree, you’ll probably have a lot of work to do before a frost comes. If a hard frost is predicted, it’s important to pick any ripe fruit to give away or use. After the frost it’s important to remove frozen fruit as soon as possible and use it immediately; otherwise it is essentially waste. Remember, citrus does’t ripen after you pick it so there is no value in picking immature fruit—your friends won’t be able to make much with unripened fruit!

How do you know when a frost is coming?

The agricultural standard is to know when the average first fall frost occurs in your area. History isn’t enough though; you’ll want to keep an eye on the weather. If you see cool, clear nights with low humidity, often following a cold front, you should be watching for an impending frost. Instead of checking with the TV meteorologists every night, we suggest you sign up for a Zeus Weather Subscription to monitor your crops. The Zeus Team will watch over your plants for you, and make sure you can eat the most fruit of your labor.

Read more here: “Understanding Frost” from Cornell, and “Avoiding Cold Damage to Home Citrus” from the University of California’s Cooperative Extension.