Home > Great Big Greenhouse Blog > October 2015 > GARDEN TALK with DOUG - OCTOBER AND OUR FIRST FROST


Well, did some of you experience frost the weekend of October 17?  I know that I did not and my summer annuals are still blooming.  Time is soon for a good, hard frost.  So, are you wondering when we all had the same low, freezing temperature, why some homeowners experienced a frost and others did not? There are some good, scientific reasons as to why.
                Early fall frosts are usually caused by radiational cooling.  This occurs on a calm and clear night when heat from the earth radiates upward into a cloudless sky.  As a result, there is a cooling of the soil and plant surfaces as well as the layer of air near the ground.  If the temperature drops below 32 F, a frost occurs.  On a windy night, there is mixing of the warm upper air with the cool lower air and frost is less likely.
                On a warm, sunny fall day our soil will absorb heat.  It releases this heat at night and can warm the plants by several degrees – enough to save tender plants on a frosty night.  One gardening practice to help protect plants is with water.  If our soil is moist it will conduct the absorbed heat from the surface down several inches.  Dry soils do not conduct heat well.  Another gardening practice to protect our plants is the use of mulch.  Mulch will act as an insulator of heat during the day and release this warmth at night.
                Do you ever wonder why farmers will use a sprinkler system at night to protect their plants?  This practice works because water gives off heat as it freezes. 
                Bottom line, the other weekend I did not have frost in my yard.  I watered all my plants that day and I recently applied a fresh layer of new mulch.  Another reason for not experiencing a frost is because I get ground protection from all the trees still in leaf on my property.
                Eventually the cold temperatures will set in for the season.  But, until this happens our soil temperatures continues to be warm which is allowing for a great fall planting season as we get ready to enter November.  So, don’t stop planting just because of the calendar month.  Now is a fantastic planting season.
Posted: 10/28/2015 by Doug Hensel | with 5 comment(s)
Tom Vanburg
Funny thing, I remember the Oct 17 frost, it's killed off most of the plants in my garden!
8/10/2017 8:49:15 AM

I planted hollyhock seeds for Fall planting. They are sprouting and about a 1/4" tall How and when do I protect them from the winter? Thank you for helping me, I have searched on internet it discusses older plants but not young seedlings.
11/7/2015 8:02:04 PM

I read in a container gardening blog that one should water before a freeze (which I did) but didn't know the science behind it. Thanks for enlightening us Doug. BTW my annuals look good too!
10/30/2015 2:16:24 PM

Very interesting - now I can tell my granddaughter the answer to her frost question!
10/29/2015 4:13:54 PM

Thanks, Doug

Now I know.
10/29/2015 2:41:06 PM

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