How to Calculate Soil Temperatures

Transplanting seedlings or planting in cold soil can lead to gardening disasters.

Most home gardeners know how critical the factors of water, nutrients and sunlight are when it comes to growing plants. Another critical factor in cultivating a garden is soil temperature. Plant vegetables in soil of the wrong temperature, and you may retard their development -- or stop them from growing altogether. Soil that is too cold can also encourage seed rot and even disease. In addition, according to Green Cast, "certain pests thrive in certain soil temperatures." Planting in soil of the correct temperature is imperative.

Things You'll Need

• 12-inch screwdriver
• Dowel
• Thermometer

Instructions

1. Mark your dowel. Make marks at intervals of 1, 2, 6 and 12 inches to facilitate measuring the corresponding depths.

2. Find a spot that is shaded from the sun. If you take your measurement in direct sunlight, your reading will be skewed.

3. Insert your screwdriver into the ground. Push it down to a depth of 12 inches. Be sure the circumference of the resulting hole is large enough for comfortable insertion of the thermometer.

4. Insert your dowel. To begin, insert it to a depth of 1 inch.

5. Insert the thermometer. Make sure the bulb of the thermometer rests firmly against the soil. Leave the thermometer in place for 1 minute.

6. Pull the thermometer out of the ground and record the reading.

7. Repeat Steps 4 through 6, but take measurements at 2-inch, 6-inch and 12-inch depths.

8. Perform Steps 2 through 7 at different times of day. Take readings at the various depths in the morning (9 a.m. to 11 a.m.), afternoon (2 p.m. to 4 p.m.) and evening (6 p.m to 8 p.m.).

9. Calculate the average reading per depth. For example, add the three readings taken in a single day at a soil depth of 1 inch. Then divide the sum by 3. The result is the average soil temperature for that location at the 1-inch depth.

Tips & Warnings

• You can find a soil temperature thermometer at a nursery or gardening retailer.

• Whatever thermometer you use, be sure it can record temperatures as low as 32 degrees F (the freezing point).

References

• RAIN: Soil Types and Testing
• Augusta Chronicle: Temperature of Soil Affects Plants' Growth

Resources

• Green Cast: Daily Soil Temperature Map