thanks for that everyone - I'm not clear why the sand has to be wet,
doesn't the heat dry it anyway? *And should the thermostat be in the
sand or near the seedbed? I'll probably put three little propagators
on the top to hold the pots etc and assumed the thermostat would go in
one of them. Cheers- Hide quoted text -

- Show quoted text -

The reason for the sand being damp is so they the heat will spread
through the bed, dry sand is a very good thermal insulator and that's
not what you want in a heated bed.
If you place a sheet of polythene on top of the sand it will keep the
moisture in the bed and will prevent the roots from the pots, trays
etc from geting into the sand.
David Hill