Tips From the Potting Bench: Soil Temps and Timing

By RITA JACINTO, Flying Blue Dog Farms

The signs of spring are everywhere and each day is becoming more urgent. The peepers are croaking their peeper songs, the flowers are blooming with abandon and bird song greets every dawn. And, best of all are the late winter rains.
The winter crone is loosening her grip as the increasing light strengthens the spring maiden’s return. This isn’t to say that the old crone doesn’t have a blast or two of winter left in her so be considerate when planning on what to plant and when.

Timing is everything so just how do you tell when to do what? One way is by the calendar. Generally speaking the USDA says our last average frost date for spring is April 15.  Now, average last frost date is not the last frost date though it does give us a good benchmark to plan by. Dates on a calendar can be fickle though so in addition to knowing the average last frost date there is another, more surefire way to know if conditions in your garden are right for sowing or transplanting certain seeds and plants.

Take your soil’s temperature. That’s right, get a thermometer, any stick thermometer will work, though for a few bucks you can buy a special soil thermometer that has a protected metal tip so jabbing it into the soil wont destroy it.  Air temperature can be deceiving, really warm during the day and still cold at night means the soil, the bed you are tucking your tender plants or sowing your nascent seed into, can take a long time to warm up to root and germination friendly warmth.  To take the soil’s temp, place your thermometer in the ground around 6 inches deep. This is the depth where your plant’s roots will be living. It’s a good idea to make a pilot hole with screw driver.  Record the temperature around mid-morning for a few days and average the reading out. Be mindful that different areas of the garden can have differing temps and in general raised beds will warm up faster than open garden beds.

Knowing your soil temperature gives you the most accurate information about when to direct sow which seeds, transplant starts and even lets you know what pests might be up to.

Soil Temps for Seed

40 degrees: lettuce, kale, spinach and peas
50 degrees: onions, leeks, turnips, chard
60 degrees: Broccoli, cabbage, cauliflower, carrots, beets and beans
70 degrees and higher: tomatoes, peppers, eggplant, melons, cucumbers, squash and corn

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