Understanding Your Growing Season: Light Frost vs. Killing Frost, Hard Frost, or Freeze
When late fall arrives, you may start to see frost on the ground when you look out the window in the morning. Depending on how cold it is, you may see some frost before you see a freeze. What's the difference?
- A frost (ice crystals forming on surfaces) generally happens when the air temperature is between 36-32°F.
- A freezehappens when air temperature dips below 32°F. The colder it gets, the more damage you'll see to annual and perennial plants. A hard freeze is usually between 28-25°F, and a killing freeze is 24 degrees F and below.
How To Prepare For Frost
- With a killing frost, tender annuals are killed down.
- With a killing frost, perennials will show damage on their leaves, buds, and blooms.
- Some fall wildflowers are exceptions, with special traits that keep them blooming so they can fulfill their botanical objective of ripening their flowers into seeds. Many sunflowersandastersare in this group, often blooming right through the first frosts.
Learn more about plant lifecycles: The Difference Between Annuals, Perennials, & Biennials
Does Frost Make The Leaves Turn?
No. The changing color of leaves during fall is a completely separate phenomenon from the falling temperatures. Leaf color change is caused by the shortening of days from summer to fall. Interestingly, the brilliant fall color is there all summer, but until fall, it is hidden by the production of (green) chlorophyll. As days shorten in fall, leaves shut down their chlorophyll production, and their real pigments are revealed.
