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Author Topic: Winter Greenhouse Regime  (Read 11613 times)

David Nicholson

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Winter Greenhouse Regime
« on: December 19, 2010, 11:55:27 AM »
If, as the experts! seem to think, we are in for a spell of exceptionally cold winters in the UK I, for one, will have to re-think my current winter greenhouse growing regime. In spite of a bad winter in 2009, although it didn't start as early as this one, and, as far as I can remember, 2008 wasn't great, my winter regime doesn't differ a lot from my summer regime. My current winter regime stems from my Primula and Auricula growing days (I mainly grow bulbs now) and of course they don't mind frost at all. Increasingly I have been leaving my two top vents closed but my two side louvres are open all year round and one glass pane is removed from the door and covered with wire mesh. So, really the only difference between summer and winter is closed top vents and me waving a few sheets of fleece around.

I grow my bulbs mainly in square plastic pots stood on staging (so I can cram as many pots in as possible!) so not having a plunge heating cables are not an option. I'm seriously thinking about an electric heater and keeping the greenhouse as near frost free as possible but given projected increases in electricity costs I would need to consider how to conserve heat and that must include re-placing the glass in my door and closing my side vents. My mind goes back to my earlier white fly farming (Fuschia growing!) when I used to attempt to line out the greenhouse (aluminium)with bubble wrap with varying degrees of failure because it invariably fell off whatever I did.

Others must already have gone through this thinking, and maybe some others, like me, are going through it now. I would welcome some thoughts.
« Last Edit: December 19, 2010, 01:49:13 PM by David Nicholson »
David Nicholson
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mark smyth

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Re: Winter Greenhouse Regime
« Reply #1 on: December 19, 2010, 12:07:49 PM »
Good question David.

Mine hasnt changed except now that my species Pelargonium collection is dead I no longer heat the benches. I have four louvres on each side that have remained open and it just occured to me that my Scilla linguata collection is frozen again and I forgot about them. Maybe it's time for me to start heating plunges again.
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Martinr

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Re: Winter Greenhouse Regime
« Reply #2 on: December 19, 2010, 12:43:51 PM »
I refuse to even consider any heat...it's too far from the house to the greenhouse to lay a cable for any reasonable amount of money. My strategy in Winter is to keep everything as dry as I dare. Anything that doesn't survive is replaced once or twice but after that I give up. At least now I do have everything plunged in sand which helps. Louvres and doors stay open all year, cold wind being preferred to Botrytis.

David Pilling

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Re: Winter Greenhouse Regime
« Reply #3 on: December 19, 2010, 02:46:55 PM »
I learnt in the previous Winter, that the top of a greenhouse is colder than the bottom. I had various (not very) hardy bulbs growing on the top shelves, and there was the effect of the leaves being OK but the bulbs turned to mush. The same species in contact with the base of the greenhouse were OK. Outside things in pots suffered, things in the ground were OK.

Conclusion bulbs are designed to grow in the warm earth and not in pots in the cold air.

It is also coldest up against the glass, so I've shifted things a couple of inches away from it. Stuffing bubble wrap in the gap between pot and glass would have been good.

This time I've tried, just for interest, to keep the greenhouse frost free. I set off by putting two buckets of hot water in at night, relative to the size of the greenhouse they will absorb a lot of cold. As it got colder, I moved on to a small parafin lamp, the sort of thing that once minded holes in the road, runs for maybe 24 hours. But last night was too cold for that.

I've got the greenhouse completely closed up at night. Rot is a worry, not so sure if it applies when temperatures are below zero and the air is dry.

How much heat depends on how big the greenhouse is, how cold it gets. Here right up to the sea, temperatures aren't supposed to go below -3C. In that situation the cost will be modest.
« Last Edit: December 19, 2010, 02:49:24 PM by David Pilling »
David Pilling at the seaside in North West England.

majallison

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Re: Winter Greenhouse Regime
« Reply #4 on: December 19, 2010, 04:15:21 PM »
I've an 8' x 7'6" greenhouse which I'm trying to keep frost-free (it's full of Nerines, some pelargoniums & echeverias); I've clipped bubble-wrap to all the struts, so the thing is more-or-less insulated on the roof & all sides; I don't have a thermostat, only a max-min thermometer & the Met Office forecasts & I've been using an electric fan heater when the temperature is -3 degrees C or below (down to -10 last night), a paraffin heater if it's -1 or -2 degrees C; electric fan heater is horribly expensive, about 6 per day when it has been running all day, paraffin heater costs about 1/3 of that to run.  I might try investing in a second paraffin heater, I'd really like to avoid using electricity, it's so expensive & not an efficient use of energy.

Think next year, I'll certainly get a thermostat as well ~ save me from leaping out of bed at 4 am in a panic to traipse down the garden in my jimjams & wellies just to make sure that the heating is functioning ok.
Malcolm A.J. Allison, Cheltenham, Gloucestershire
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Giles

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Re: Winter Greenhouse Regime
« Reply #5 on: December 19, 2010, 05:24:11 PM »
Electric warming mats might be an option, with thermostat, and fleece over the top when its particulary cold. At worst, only the leaf tips will get frosted.
(Most mail order places do them)
« Last Edit: December 19, 2010, 05:25:52 PM by Giles »

johnw

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Re: Winter Greenhouse Regime
« Reply #6 on: December 19, 2010, 06:49:09 PM »
Electric warming mats might be an option, with thermostat, and fleece over the top when its particulary cold. At worst, only the leaf tips will get frosted.
(Most mail order places do them)


Malcolm - For the few days that you are likely to be cold I would crank up the electric heater.  I don't think the Nerines will like the heating mat and if they get any frost they will go down as Mark found out.  We paste buble wrap on the aluminum greenhouse door and use sheets of styro over the northside glass.  Propane heater + electric back-up set at 4c, I wouldn't like to think what our small greenhouse costs to heat but probably in excess of 300/yr.

johnw
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PeterT

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Re: Winter Greenhouse Regime
« Reply #7 on: December 19, 2010, 08:30:32 PM »
I refuse to even consider any heat...it's too far from the house to the greenhouse to lay a cable for any reasonable amount of money. My strategy in Winter is to keep everything as dry as I dare. Anything that doesn't survive is replaced once or twice but after that I give up. At least now I do have everything plunged in sand which helps. Louvres and doors stay open all year, cold wind being preferred to Botrytis.
I have to agree with you Martin. I tried bottom heat and it caused so much drying that corms went dormant before they had regrown. I did not dare water in hard frost. many things are hardier if kept on the dry side and if growth is delayed by this tecnique. One has to watch carefully for signs of premature dormancy though.
living near Stranraer, Scotland. Gardening in the West of Scotland.

PeterT

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Re: Winter Greenhouse Regime
« Reply #8 on: December 19, 2010, 08:40:06 PM »
I've an 8' x 7'6" greenhouse which I'm trying to keep frost-free (it's full of Nerines, some pelargoniums & echeverias); I've clipped bubble-wrap to all the struts, so the thing is more-or-less insulated on the roof & all sides; I don't have a thermostat, only a max-min thermometer & the Met Office forecasts & I've been using an electric fan heater when the temperature is -3 degrees C or below (down to -10 last night), a paraffin heater if it's -1 or -2 degrees C; electric fan heater is horribly expensive, about 6 per day when it has been running all day, paraffin heater costs about 1/3 of that to run.  I might try investing in a second paraffin heater, I'd really like to avoid using electricity, it's so expensive & not an efficient use of energy.


Quote from: PeterT on Today at 07:52:26 PM

I don't have any heat on, the glass round the sides is only to keep cats away from the sand. I have found a roof alone controls the moisture level which allows me to regulate the growth patterns of the plants and If I get it right   Undecided many supposedly tender plants will survive freezing. Much of this green house is oncos so maximum air flow.
A clever Idea to store warm air but it would require a lot of storage to provide enough warmth to mitigate a frosty night.
I read of a tecnique of temperature control where steel drums of water are put in a green house. During the day the glass traps heat and the water warms up, at night the water acts as a radiator delaying the night frost. When the sun heats the green house the next day the drums of cold water slow down the temperature rise. The overall effect is to moderate the temperature fluctuations


Think next year, I'll certainly get a thermostat as well ~ save me from leaping out of bed at 4 am in a panic to traipse down the garden in my jimjams & wellies just to make sure that the heating is functioning ok.
Many Nerines will take some frost and certainly some Echiverias provided they are not damp and trying to grow as though it were spring. In cool temperatures I should worry about the humidity from the parafin heaters for the Echiverias. I had Nerines gibsonii, platypetala, hirsutum, masonorum, filifolia, 'flexuosa alba', and others survive without heat last winter. I lost pudica which I have grown without heat for 6 or 7 years.
« Last Edit: December 19, 2010, 09:04:56 PM by Maggi Young »
living near Stranraer, Scotland. Gardening in the West of Scotland.

Diane Whitehead

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Re: Winter Greenhouse Regime
« Reply #9 on: December 19, 2010, 09:17:25 PM »
I lost too many potted South African bulbs in a small unheated plastic
house.  Five years old, almost old enough to bloom, and mush because
we had a few days of -8C.  The weird thing was that large pots outside
on the ground survived, but ones on a wire bench in the greenhouse froze.

Then for a couple of years I put in gallon or larger pots of hellebores so
they could be sold in bloom at a February club sale.  I covered them with large
bubble wrap.  Oh joy! said the rats - a cozy spot, with delicious food too.
They set up camp under the bubbles and ate the flower buds.

So now anything potted comes in to my large attached greenhouse for
the winter.  It is two stories high, 8 by 12 metres.  It is large enough that
its temperature remains fairly constant.  It can approach freezing, and
might have once when a mango tree died, but generally is a couple of degrees
 warmer than outside. I have a wood-burning boiler in  an adjacent space, and
 a ~500 gallon tank of water to hold the heat, but I only heat it for parties.
Diane Whitehead        Victoria, British Columbia, Canada
cool mediterranean climate  warm dry summers, mild wet winters  70 cm rain,   sandy soil

tonyg

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Re: Winter Greenhouse Regime
« Reply #10 on: December 19, 2010, 10:05:38 PM »
I refuse to even consider any heat...it's too far from the house to the greenhouse to lay a cable for any reasonable amount of money. My strategy in Winter is to keep everything as dry as I dare. Anything that doesn't survive is replaced once or twice but after that I give up. At least now I do have everything plunged in sand which helps. Louvres and doors stay open all year, cold wind being preferred to Botrytis.
I'm with Martin, for much the same reasons and adopt a similar approach although most of mine are in square plastic pots unplunged.  The watering balance is more of a challenge with those bulbs which are in leaf at this time of year.  I don't grow many South Africans though.

ArnoldT

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Re: Winter Greenhouse Regime
« Reply #11 on: December 19, 2010, 10:19:56 PM »
I have a lean to greenhouse attached to the house on two sides.  I have used a small dairy barn  heater set  to go on at  45F.
I put eight black 5 gallon pails with lids on the bench on the east facing side.

I have a thermometer probe in one of the pails.

During daytime the water in the pails  heats up to about 50 F and the greenhouse heats up to around 45 F with outside temperatures currently running at around 25 to 30 F.

Each 5 gallon pail can store about  41 BTU's per degree F rise

With 8 pails full of water each degree rise results in a gain of 330 BTU's.
Arnold Trachtenberg
Leonia, New Jersey

ArnoldT

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Re: Winter Greenhouse Regime
« Reply #12 on: December 19, 2010, 10:21:07 PM »
Sorry should be  5 gallon pails with lids on the under bench on the east facing side.
Arnold Trachtenberg
Leonia, New Jersey

Diane Whitehead

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Re: Winter Greenhouse Regime
« Reply #13 on: December 20, 2010, 12:32:34 AM »
I was inspired by an interesting book, Solviva, by Anna Edey. 

She ran a large greenhouse, partly heated by the sun and partly by
chickens living in it.  (She tried to get her sheep to stay inside too
but they preferred the cold outdoors.)  She was even growing enough
tomatoes to sell in midwinter.

Then I started to think more about it.  I used to keep chickens and
I'd have an allergic reaction whenever I cleaned out the coop.  Not
a good idea to fill my greenhouse with feathers and dust.

And the solar heat.  Right!  Before I designed my house back in the
60s, I read all about that.  I faced all the windows south, expecting
solar gain.  My calculations did not take into account  how high all
those conifers were and how low the winter sun's trajectory is.  Or
our maritime cloudiness. On the few winter days when we actually
had sun, I would have it for about an hour when it managed to shine
from the unobscured sky above the road. 

So I get NO solar warmth, but the infrequent winter sun is cheering.
Diane Whitehead        Victoria, British Columbia, Canada
cool mediterranean climate  warm dry summers, mild wet winters  70 cm rain,   sandy soil

Maren

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Re: Winter Greenhouse Regime
« Reply #14 on: December 20, 2010, 01:37:48 AM »
Hi, I have greenhouses in remote places (no electricity). I have for years now lined them with large bubble plastic inside AND out. That saves me a lot of heating costs. Heating is by gas bottles, a pair at each greenhouse with an auto changeover device.

To fix the bubble plastic in place, I use elasticated curtain wire with small hooks screwed into the ends. On my aluminium greenhouses, I have drilled small holes into the frame to anchor the hooks. On the wooden greenhouse I screw in larger hooks to which I attach the curtain hooks.  It works really well. The double layer keeps out the windchill.

The bubble insulation has to be three layered, two smooth outer layers and the bubble wedged in between. It's a bit more expensive than the two layered bubble, which is smooth on one side and bubbly on the other. The latter is rather flimsy I find and it only serves for packaging.

I have a greenhouse on an allotment where I grow Cymbidiums. It is on a hill exposed to fierce easterly winds, which used to rip off the bubble in no time. I have overcome this by putting shade netting over the external bubble layer. This is easier to fix to the structure and I haven't lost my insulation yet, fingers crossed.
« Last Edit: December 20, 2010, 07:14:54 PM by Maren »
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