Judging when it’s safe to plant plants in the spring can be tricky all due to freeze and frost. The average last frost date is a date gardeners look forward to because it means it’s time to start planting!
Even with knowing the average last frost date there’s still uncertainty. As we face climate change the weather is becoming more unpredictable and unsteady. While even the most savey gardeners can look for clues, there’s always the chance of late season freezing temperatures, snow, or frost.
What is Frost? Frost is simply water vapor (water in gas form) that has frozen and condenses and becomes solid. The surface of the object is below freezing and the water vapor on the surface freezes. When this happens on plants, the cells inside the plant burst and die, because as water freezes it expands. This is why frost damage on leaves can turn the leaf into slime.
Average Last Frost Date. The first step is to be familiar with your area’s average last frost date. The average last frost date is the average date during the spring your area should be no longer susceptible to frost.
In general, there’s still a 10% chance that the actual last frost date for any given year will happen past that date.
Different regions in your state may have different average last frost dates, so it’s important to find information specific to your region and city. It’s also important to take observations of your own property. Low points are more susceptible to frost because that is where cold air will collect.
You can find information for your average last frost date on Plantmaps.com. Just enter your zip code, find the column for ‘Average last frost date’ and click on the coordinating box of your state’s map. It will show a list of cities and their average last frost date. Here are Kentucky’s average last frost dates.
I think it’s important to not go by the last frost date according the plant hardiness zone maps. This is because frost formation can be influenced by many factors like altitude, topography, and the heat island effect.
In my zone of 6b, the average last frost date is April 20th, but when I look at information for my city, it shows an average last frost date of May 1-10th. This is a large difference, so finding specific information is important.
You can find more Frost and Freeze information on the National Weather Service website. It includes information about frost and freeze date records, and yearly averages. Here is this information for Lexington, Kentucky.