Theory on Keeping Soil warm to Keep a Durian tree Through a NSW Winter?

One cubic metre of soil weighs roughly 1.6 tonnes and acts as a significant thermal battery. Once warmed, that mass of soil can retain heat for many hours, especially when protected by mulch, windbreaks or a greenhouse structure.

Calculations show that raising one cubic metre of soil from 5°C to 15°C requires a substantial amount of energy. However, after the soil has reached temperature, the challenge becomes maintaining that warmth rather than continually reheating it from scratch.

A practical approach is the use of a low-power soil heating system operating during the coldest part of the night. A heating load of approximately 350–500 watts running for around 8 hours between dusk and dawn consumes between 2.8 and 4.0 kWh per night. At current NSW electricity prices, this equates to approximately $90–$120 over a three-month winter period.

From a grower's perspective, that's a surprisingly small cost. For around $120 over an entire winter, it may be possible to maintain the root zone of a young durian above the critical 15°C threshold, particularly when combined with deep mulch and protection from wind. Rather than attempting to heat the surrounding air, the energy is concentrated where the tree needs it most – at the roots.

The concept is simple: use a cubic metre of soil as a thermal store, add a modest amount of heat during the coldest hours, and let the soil mass buffer temperature fluctuations through the night. If successful, the annual winter heating cost for an experimental durian planting could be less than the value of a single premium durian fruit.

For NSW growers interested in pushing tropical boundaries, the question may not be whether durians can survive winter, but whether maintaining a warm root zone for approximately $120 per season is enough to make them thrive.