"Bertie Doe" wrote in message
...
I have a surplus to requirements coal bunker. With the help of a neighbour,
I've managed to shift each concrete panel of the bunker, from the house to
the allotment.
The intention is to re-assemble the bunker into a handy coldframe. Each
panel is approx 3' x 3'. I will screw to rows of battening, about 9" and
18" from the top - this will allow me to lower the plants, as they get
taller.
This will leave a space of about 18" at the bottom of the new coldframe.
Suppose I was to fill this space with fresh material from the composter. I
noticed when topping up the composter with household waste today, that the
contents were starting to warm up a bit, despite the recent cold weather.
Can anyone foresee any problems? I've got an outdoor max/min thermometer,
so there should be no danger of me overcooking the seedlings - I hope!

This is the way old time gardeners provided bottom heat in cold frames - a
layer of active compost underneath the beds.