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Heated Bed Propagation

The request was to design, supply and construct heated sand beds for the propagation of plants. The particular crop benefits from the implementation of bottom heat in the propagation stage, therefore we designed a system of pipes to circulate the heated water around the beds to apply the correct temperature with full automatic control. The water is heated by a commercial boiler although in the future an air source heat pump or solar panels could be installed.

  • The existing stone base was stripped of Mypex and timber for disease reduction
  • Tanalised timber frames 150mm high, supported by steel rods, were installed to contain the sand
  • 50mm polystyrene insulation sheets with drainage holes laid in the bottom
  • 16mm PE heating pipes, connected to a header manifold, and spaced at 30cm apart
  • A plastic mesh was overlaid on the heating pipes to ensure they remain buried
  • 100mm sand up to board height
  • A drip irrigation system was laid on the top of the bed to allow under crop irrigation. This will leave the crop canopy dry whilst keeping the sand moist to ensure uniform heat dissipation.

In addition to the sand beds, we were asked to install a misting system for cooling/humidification over the crop. This consisted of foggers spaced at 2m x 1m and 1.2 m above the crop. The misting system is controlled by an evaposensor controller which will monitor the in-crop environment and trigger the misting at the set point. The controller can be used to wean the crop once rooting is advanced enough.