Allotments 4 All

Ancellsfarmer described in the recent tomato thread that he intends using bricks in the greenhouse between newly planted tomatoes to retain a bit of the day's warmth. 

Here is another tip:  Milk bottles filled with water, warm up during the day and give off heat slowly after the sun goes down.  Even better is 'brown water'.  This is diluted 'brown' comfrey fertiliser liquid in water.  The darker liquid takes up more heat than clear liquid.  When the little bottle storage heaters are no longer needed, the contents are useful for watering/fertilising the plants.

Yes, water has a very high specific heat capacity compared to most other materials. Having a water tank inside the greenhouse works well, either a dip tank, or a butt fed from the gutters. Or a couple of full watering cans ready for use (heat capacity, and warmed water ready for watering). If building new greenhouse staging, one could use salvaged radiators. I've seen photos by Bob Flowerdew using radiators laying flat as paths in a polytunnel.
I use bricks outdoors too- under aubergine plants, and inside cloches.