How many weeks' holiday a year are there? <a href=" http://messingengroef.nl/ropex-testimonials.pdf ">where to buy ropex</a> I also use heat sinks. This is a fancy way of saying "I have a stone floor and a water butt", but this is how it works: the heat of the day is stored by such things and released at night, so smoothing out the temperature difference (it's useful in summer too, to keep the greenhouse cool). I move the plants and water butt to the north side of the greenhouse so that maximum sunlight falls on the stone floor during the day. The water butt is the important thing, as water is three times more effective as a heat sink than stone: a line of water butts topped with planks of wood to make a working surface would be a space-efficient way of taking the chill off the night time greenhouse.