2016 Monitoring Soil Temperature

Over the last few weeks, it has been fun to watch the snow recede back to higher elevations and to see soil present itself once again on the valley floor. My personal Facebook feed is filled with photos of friends who, like busy little bees, are working continuously on planning and planting their future gardens. It is so easy to be taken in by the warm, sunny days of early spring. It makes a gardener antsy to get their hands dirty. We take off our sweatshirts and let our pale skin soak in the warm rays; retiring to the comfort of our house when the sun begins to set and the temperatures again dip down to near-freezing at night.  However, the seeds that we sow outside in this early season do not have the luxury of finding warmer accommodations once the heat of the day dissipates and it is often easy to forget that, even though we are comfortable and warm while working in the yard, the soil in our gardens is often still very cold, damp and unpleasant for seedlings. For this reason, I thought that it would be good to write a brief reminder about the importance of monitoring soil temperature as part of your gardening routine.

When sowing seed in the spring, a gardener should monitor the temperature on the top 3-4 inches of garden soil. This is the zone where germination and root development will be taking place.  Although most seeds are sown within the top ½ inch of soil, the first 3-4 inches will be were root development occurs. This is also the depth that will start to indicate the overall warming profile of the entire soil column. In the spring, we oftentimes have days where the upper-most layer of dirt will feel warm and comfortable to the touch. However, by digging in just a little deeper, it is easy to feel that the earth below has still not warmed and is holding on to the residual cold of winter.  If we allow our excitement to outweigh our rational thoughts we will oftentimes plant seed a week too early and many of our efforts will be wasted due to fungus, rot, damping off, and poor or delayed germination. For those seedlings that do germinate, their growth can be permanently stunted and will oftentimes be overtaken by seeds planted even a week or two later. Best to practice a little patience and diligently monitor soil temperature before planting.

Checking soil temperature can be incredibly easy to do and does not require special equipment. Although a person can purchase specialized thermometers from garden supply stores, a simple meat thermometer will suffice for probing the upper zones of garden soil. Like probing a turkey during roasting, a gardener only needs to stick the probe end of the thermometer down into the soil and then wait for the instrument to calibrate. With a black sharpie and a ruler, it is possible to make markings in 1” increments on the probe of the thermometer. The thermometer can be moved up or down so that temperature can be measured throughout the 4” column of soil. This time of year, you will see a drastic change between surface temperatures and deeper measurements. Wait until the soil has reached at least 55 degrees Fahrenheit at depth and 60 degrees at the surface before sowing cool weather crops. For warm season crops, the soil profile should be at least 65 degrees Fahrenheit at depth as well as at the surface. This simple technique will help increase your germination and over-all gardening success. Good Luck and Happy Gardening!