Home > Great Big Greenhouse Blog > March 2015 > GARDEN TALK with DOUG - SOIL TEMPERATURE


47 DEGREES – This is our current soil temperature as of Thursday, March 26.  And, with our extended weather forecast I don’t see our soil temperature changing much in the upcoming days.  I have been posting our soil temperature on a billboard inside the garden center for the past few weeks.  Customers have stopped and asked about the importance of this information. So, why is soil temperature so important to gardening and landscaping?  The answer is relatively simple:  the soil temperature, not the air temperature, is the engine as to when it is safe to be planting, applying chemicals, and when our plants begin to flower.  Have you noticed this year that are forsythia plants are now just beginning to bloom.  In years’ past we have had our forsythia shrubs showing color in mid to late February.  And, we use our forsythia flowers to determine when we need to apply our crabgrass pre-emergent.  So, this year it is the right time to apply the pre-emergent now.  In past years this timing could have been too late.
                Gardeners can’t always rely solely on the calendar or the famous Old Farmer’s Almanac to tell them when it’s time to plant.  This is so true especially after our past couple of winter seasons.  Mother Nature is in complete control, not a calendar or a gardening book, as to when it is safe to begin doing certain gardening chores and landscaping.
                Bottom line:  Soil temperature is critical to gardening success.
                To measure the soil temperature, I use a soil thermometer.  To take a reading simply insert the probe into the soil and leave it in the soil for a minimum of 5 minutes.  After 5 minutes pull it out and you have the temperature of your soil.  We sell these thermometers in our Garden Pharmacy for only $7.99.  So inexpensive but yet such valuable information to have available when gardening and landscaping.
                Plants that are started in cold soil may grow slowly, develop poorly, or succumb.  When soil temperatures are low certain nutrients are made unavailable or less available to plants.  So, how warm is warm enough?  That depends .  Cole crop, sometimes referred to as cold crop leafy vegetables such as lettuce, spinach, cauliflower, onion sets, broccoli, and others will germinate and grow when soil temperature is in the mid-40’s – like now is the time to plant.  Conversely, warm season vegetables and herbs, such as tomatoes, squash, cucumbers, basil, thyme etc. prefer a soil temperature in the mid-50’s to mid-60’s – like needing to wait until late April or the first of May to plant. 
                Now you see why I have fun talking to people about soil temperature and using this key information to help them make the right decision at the right time.
Posted: 3/26/2015 by Doug Hensel | with 1 comment(s)
Deborah Pridgen
I always trust Doug' advice.
4/2/2015 2:06:30 PM

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