Retaining heat in cold greenhouse

Try searching "Solar Greenhouse" on the net, the principles involving blocks and containers of water are in the right direction. I’ve got designs for greenhouse staging constructed using large drums full of water and concrete blocks in a book called “Gardening under cover” by William Head

A fresh manure hotbed would help.....but they can be rather labour intensive. (As well as smelly!)
I've found that there's a heck of a difference between the temp at the base of the greenhouse and the temp in the eves............maybe moving tender plants to a higher position would help?

Many thanks for these ideas, King Carrot and Snadger, some of the suggestions for "solar greenhouse" are really novel (and leave you wondering why you pay out for electricity and oil for your home let alone a greenhouse!) and several are very straightforward (e.g. I'm now going in search of 120 empty beer cans at which point i might lose interest in green heating...). I've never tried the fresh manure trick - I understand the Victorians used to grow pineapples using this technique... but will give it a go. Thanks again. b.

Some solar panels and computer fans will circulate the air for you to help even the temperature a bit. If you ask nicely at your local chippy they might have the polystyrene boxes that fish come in. the bottoms make good oversized "seed trays" as thay have drain holes in and it's easy to put more in if you need too and the tops make good trays to stand pots on. they polystyrene is warm to the touch so helps and being white reflects light - usefull at time of the year when it's dull - like spring.

Hello,
I have been carrying out a small trial in my veg plot to see just how much heat a cloche retains. So far the temp inside the cloche is always at least 3 degrees higher than the outside temp. I took these readings in the morning before the sun was on the cloches. I planted some tom seedlings under the cloch to do a mini trial. After two frosts they are still ok. I think the difference here is that the soil is warmed and so gives off heat overnight and the cloche retains that heat.

Thanks PoshCloche (exploring your name) and Nick - good ideas, I always save polystyrene and it's a very good insulator. Updating the suggestions received so far, I reckon the solar greenhouse beer-can air warmer will prove a winner (all friends and neighbours now saving cans, urged to drink more!) I hadn't realised that the gravel floor was a natural asset (evidently needs to be deeper for best effect); storing water butts in the greenhouse full of water throughout winter (which retain heat on a low calibre 'hot' water bottle principle) looks worth a try Winter 2009/2010. I've run into difficulties with the hotbed system, reading that it needs to be a minimum of 4 feet deep (and only lasts a few weeks before needing replacing) - if I dig a large 4' hole in the greenhouse i reckon it might collapse... so rethinking December pineapples. I can get the necessary fresh stuff and such a cool idea (in a manner of speaking...) but perhaps better outside the GH with a temp cold-frame plonked on top after it's been dug and filled?

Anyone know of a small windmill to DC charge a small battery to run a mini-fan such as N's computer suggestion? Looking that up I learned B&Q have dropped their much criticised wind generator (much more elaborate than anything I was contemplating). But there must be a mini-one available somewhere? I'm not looking to replace the Electricity Board, just charge a 6v battery to run a light bulb and mini-fan for a couple of hours in 24.

Must be doing something right as everything survived the would-be minus 4C of last week (Max/Min recorded +2C as the lowest) so at least it's having some effect along the lines as outlined by PoshCloche. I'm not chancing anything really tender yet but toms survived OK.

Without becoming Green overnight one interesting claim I met via Google is that the sun provides daily SIXTEEN TIMES the maximum energy needs of the whole planet. Some of it of course is delivered in an inconvenient way (e.g. middle of the Sahara) but quite a bit is also local even in Winter so for the moment i remain obsessed with beer cans!
b.

I like the idea of a heat adsorption/release. I've just bought these two 55L containers on ebay. Going to make nettle/comfrey fertiliser in them. If I paint them black and keep them in my greenhouse they should adsorb heat during the day which will help the brewing and then release heat at night. Will paint them black as well to help the heat adsorption.

http://cgi.ebay.co.uk/ws/eBayISAPI.d...2BSI%26otn%3D4

Have a look on freecycle for storage heater bricks. I picked up 40 odd a few weeks back. I'm actually intending on building a wood fired oven but if that comes to nothing they'll go into the greenhouse as storage heaters.

could you use storage boxes filled with water and tucked under the staging for heat retention?

So from reading this thread, as I have a bit of spare room in my walk in plastic greenhouse, would I be better placing my water butt inside there instead of outside?

It isn't fitted to the downpipe, I fill it with tap water.

Would this make the greenhouse a bit warmer at night?

that appears to be what other sites are suggesting. If you can paint the butt black then it'll absorb more heat during the day and should be a better radiator when the temperature drops.

D

It's one of those very dark green ones so I think it may be ok.

Fill it with hot tap water every evening and you will be fine !!

Thanks for additional suggestions.... There's also a lot of illustrated suggestions on YouTube, here's a couple to get you started:
Heat sinks in greenhouse:
YouTube - Solar Greenhouse
Beer-can heat collecting funnels:
YouTube - Brilliant Newfoundlander Invents the Solution!

b.