SEEDS AND SOIL TEMPERATURES
There’s an old saying that the time to plant seeds is when you can comfortably sit on the ground with a bare bottom. I prefer to use a soil thermometer instead of shocking my neighbours! I have a nifty, dual-purpose one that shows the soil and air temperatures at the same time. In general, the soil in wooden raised beds is warmer than garden beds, and metal and terracotta pots are warmer still. For example, one afternoon, when the air temperature was 15°C; the soil in a wooden raised bed was 12°C; the soil in an old copper in full sun was 13°C, but heavy, waterlogged clay garden soil only reached 10°C.
Moisture and soil consistency affect the temperature too. Light, aerated potting mix that’s well drained warms up much faster than dense, waterlogged clay. Interestingly, the soil temperature is much more stable than the air temperature. Early the following morning, the air temperature was 11°C, the raised bed and the copper were 12°C and