Do you heat during the winter?

You would need one massive greenhouse to be able to use straw bales as insulation, something the "Victorians" had, but it's often forgotten that the so called Victorian greenhouses were on large estates where money and space was no object.
Not much they did is practical today, I dont think.

As to the floor of a greenhouse needing insulation, I'm not sure about that, I think on very cold nights we actually get warmth coming up from the ground.
Move a pot plant during a frosty spell and its often not frozen underneath, frost only occurs on the surface, cover the surface and it doesn't freeze, this is how fleece works, it locks in the warmth from the ground and stops it escaping.
I sometimes in very cold weather put a paraffin lamp under the blankets that cover my Strelitzia etc. it provides enough warmth to keep hard frost at bay.
My cold frame has a roll down cover of silver bubble wrap, this reflects the heat from the ground back down and stops it escaping.

My greenhouse on the allotment has foam,( http://www.globepackaging.co.uk/pro... +wrap&fl=601938&ci=18911204623&network=s&pm= )the kind you use under laminate flooring halfway up the sides, it stops some frost penetration.
But its amazing how many tender plants will survive quite low temperatures if dry, I dont mean at the roots, but on the plant itself, wet frozen leaves die much easier than dry ones.

Seedlings are a different matter, and I dont think there is any real substitute for warmth.

 

I've not read fully through this thread, so won't pretend to fully understand the issues, but at least lets understand that opinions are given with the best intentions

 

In the recent cold snap I was surprised how much the temperature of my greenhouse rose during the day. We had a few days with freezing fog, and the temperature remained pretty constant (day & night) at around -1C, but during the day, heavily overcast, the greenhouse rose by several degrees. On one occasions with a couple of inches of snow on the roof, so definitely no solar gain. Perhaps heat from the soil? (Although why was the gain during the day, if outside temperature was same at night too? )

There has been chatter on HTUK about using heat from the ground to protect plants; Dave is of the opinion that chucking, say, an old duvet over a plant allows the warmth from the soil to be trapped and warm the plant. Same thing with an insulating covering of snow. He also thinks that snow should be cleared from the base of plants with tender tops - to allow heat from the earth to escape and rise up into the plant above - and his tests seem to prove his theory.

 

We did - before central heating, with Tilly lamps and such like.

 

Two things here,
(1) under floor thermal, I did put thermal blocks under both the garage floor and greenhouse floor pre laying concrete, the reason "if you've ever lived in a house thats been built on a sand or soil floor and then tiles over as i did with a cottage i once owned in mid wales, you'll soon find out that during wet spells followed by a warm spell the tiles (ground) becomes damp, no im talking a bout a house fully furnished and the furniture "cloths such as curtains etc will take in some of this damp air as will human life inside the building just by people moving around,

In the green house this change in temps, isn't what you want its a stable temp, during the freezing conditions we're talking about,
if your floor is layed on a membrane to keep rising damp out and then via thermal covering" this being glass bottles or even clay broken gravel and then concrete your giving the area more protection from the underground.

(2) ref inside the greenhouse and the air temp, "Fleece" spread over your plants will do wonders to keep them from the drop in room temp.

As for using straw and greenhouse's these days being to small,!

Ive a greenhouse, 12 feet long x 6 feet wide and ive used the straw method,
its no more taken up than the staging that in my case is used on sides and far end.
The bales take the place of the staging.

Rather than think of as many reasons why these tried and tested idea dont work why not try them for your self,?
If housing these days didnt need any form of good solid protection from the weather under them i can assure you builders wouldnt go to the cost of putting in membrane's, concrete etc.
Your greenhouse is a building but the modern greenhouse must be approx 90% glass the rest is framing ie metal/wood, And if you think about glass single glazed and the frame construction isnt enough to keep warmth in if the ground its standing on has an unprotected base, common sense must tell you this and all the evidence is looking you in the face, just look at how sunrooms/conservatories are built,
do they stand on earth flooring?
Its not much good trying to keep heat in a room if the ground area changes via the weather,
using inner ground cover such as straw on the top of your floor is simular to using carpets in your home, the bare floor bourds are not as warm as a carpeted floor,
by using straw,/ cardbourd/ etc will help keep the cold out but the answer to a complete job and a money saving one is to do your home work before you errect your greenhouse, and if you've already errected the greenhouse! you can still in the good weather concrete the inner floor to conseal the inner heat.
All the info is here all the reasons why and all the modern day building reasons why homes/ garages etc are built on solid floors.
the rest is up to you, if you want to sort out why your loosing heat, why its costing you more than you want to pay on fuels, etc the answers are here.

For those who still want to find all the reasons under the sun as to why "not" follow the advice given!!!!!!!!!!! see you here next winter on the same subject.

 

I think however overcast, there is always at least a small amount of radiated heat from the sun during the day, and the greenhouse traps it.

Not visited HTUK for a few years, but I've been using old removal blankets, (http://www.packingboxes.co.uk/removal-blankets/ ), for years to keep frost off plants in mid winter and trap the warmth from the soil.
Its basically a removable mulch

 

I've never put my greenhouse into the same category as a conservatory or house with central heating, so unless I was heating it to a high temperature during the winter I'd not bother with insulation in the floor in the UK.
If I lived in a country with permafrost it would be a good idea, but here the soil temperature inside the greenhouse, on frosty nights, will always be above air temperature, if it is unheated.
If that is the case, my conclusion is that some of that warmth from the ground will be lost to the air in the greenhouse, raising the air temperature by a small amount.
If the floor is insulated that cant happen.

 

I feel the same Pete. I'm no engineer but I think that house insulation is a different matter; it needs to keep the expensive central heating at 20C within the building, which without insulation would lose some to the ground which is at a lower temperature [than 20C]. However, for a frost free greenhouse, and thus much lower temperature, the ground's temperature is positive.

A house is also insulated to prevent cold surfaces, which is a different issue. Cold surfaces cause condensation (anyone with single glazed windows, or even old double glazed ones, will know about that from the condensation that they get on cold nights :( ). Cold surfaces in a house have two bad effects: the condensation that forms will encourage moulds or, worse, cause steel or wood to rot; and it causes the air adjacent to it to descend, causing a draught which makes the humans feel cold and turn the thermostat up, which uses more fuel. So house insulation is, in part, to create comfort and prevent condensation, neither of which is a requirement for a greenhouse.

I use an electric fan heater because that also dramatically reduces the moulds which would be caused by the condensation. The heater part has come on on each of about 4 nights this year, so far (we had -10C ...), so it is pretty frugal [by comparison to anything that has to be lit / turned on manually when cold nights are forecast]. The fan part runs 24/7 (actually on a 50% timer, so its on/off every 15 minutes), and that has completely prevented moulds etc. this winter, whereas in previous years they have been dreadful.

My heater has a very accurate thermostat, which means that I don't waste fuel heating higher than the cutoff point; some of the cheap heaters overshoot by as much as 10C (or, worse, undershoot by that which will result in dead plants :( ). I've had a logging thermometer in their this winter, and the thermostat's hysteresis has been within half a degree C - can't ask for better than that

 

Then why is it all the garden centre's have the unheated inside roofed area's with concrete floors, ? going by your theory they will have plants full of leaf mold and drying out,
Ive never seen these centre's using electric fans 24/7 and i di visit on a regular basis both winter & summer,
And what happens if during the night a sudden power cut arrives in the middle of january/febuary when the temp, can be really freezing!
Wouldn't you stand a chance of loosing your plants to this lacking in temperature!
and if so all the pre heating/fan use would have been a waste.

REF house heating being different, i cant agree, cold is cold and if you leave a house empty (no furniture etc) for a length of time with no heating (and the older houses with no membrane and soil/sand flooring) you'll soon see the effects of that house not being heated and the cold rising from the floors, Open fire place area and floor bourd on the higher level's,

I was thinking today ref how many greenhouses ive had since we've had our own homes and its 4, the first was erredted just on the soil, it was a heavy wooden greenhouse within approx 10 years the bottom wood was rotted, the winter temp was always a problem trying to keep frost out, i used a paraffin heater in those days and even then the cost wasn't really worth the use of such a heater,
The same house but a new metal framed greenhouse with a concrete base and thermal covering the membrane sheet & then concrete layed, it was worth all the effort and work laying the base and from that day on (ive since moved to france but again a repeat of this method) ive used the same way of doing the base for the larger greenhouse i now have and the garage flooring,
If i thought this was all a waste i wouldnt have repeated the method 3 times in all.
But as ive already said, it's up to who ever wants to save heat or a better way of putting stop cold moist air from rising through the ground into a confined glassed space and a good chance of frost damage,
It really is the choice of who ever wants to take what way you or myself have gone
Im more than happy with what i was shwon many years ago by someone who was a lot more experienced than i was at the time.
So good luck and good gardening.

 

Yeah, good luck moonraker

 

Many years ago when I started with greenhouse 6 X 8 I used a biscuit / sweet tin and put a 40 W bulb inside this was great for starting seeds.


Trevor

 

Got to say, that as much as I complain, the most efficient way of heating a greenhouse is electricity.

Something that has not been mentioned above is decomposing straw is full of fungi. Not something i would want near my cacti and succulents.