lemons in the greenhouse

December 2021 - Keeping the Soil Warm and Moist! Kind of…


Despite my love for citrus fruit, I can’t rationalize expending oodles of energy to create the kind of environment they prefer. The greenhouse relies on passive solar energy for heating except in the winter when outside temperatures drop below -2°C, or during prolonged cloudy weather. During these cold spells, thermal water tanks in the greenhouse are heated with a high-efficiency wood gasifier. The warmth from the tanks is circulated with horizontal air flow (HAV) to ensure the air temperature maintains at least 1°C.

As a result of these conservative practices, in December and January the greenhouse soil temperature drops to around 6°C. This is well below citrus’ 12°C limit for root elongation and their optimal soil temperature of 26°C. (see reference)


We are recording soil temperature throughout the year to help us in our assessments of plant function and health, and the activity of soil biology.


Figure 1 The Garden Greenhouse Soil Temperature (C°) at December 28, 2021


Figure 1 shows the soil temperature (°C) throughout the greenhouse December 28, 2021.

We record soil temperature with a Hanna Checktemp 1 Digital Thermometer - HI98509.


Soil Moisture

The trees throughout the greenhouse vary in size and vigour. Because each tree has its own ‘pocket’ of amended soil surrounded by a compacted C horizon with little evidence of pedogenic activity, we are recording soil moisture levels at each tree.