Allotment Gardening Advice Help Chat
Growing => Growing in Greenhouses & Polytunnels => Topic started by: ghost61 on October 09, 2014, 11:39
-
I am thinking about heating my greenhouse on the allotment, as I have some citrus trees in pots inside as well as kiwis. No electricity obviously, and I'm worried about paraffin heaters in case of idiots coming on site and doing some damage....will bubble wrap and fleece be sufficient as an alternative (also means I don't have to go down to check fuel etc).
What do others do or recommend?
-
Would one or two of the clay pot warmer thingies work with 8-hour tealights to keep the frost away? Not sure how that would work in really cold weather.
-
In the absence of electricity you won't [AKAIK] be able to use a decent thermostat - so you will have to light on the nights you think it may be cold, and extinguish the following morning.
Bottle Gas will have a crude bi-metalic strip type thermostat, so will only use gas for a pilot light when temperature is satisfied (but the inefficiencies of the thermostat will mean that the greenhouse over- (or, perish the thought!) under-heats by maybe as much as 10C before the thermostat cuts out.
Paraffin has no thermostat, plus also the risk of the wick burning unevenly, and sooting-up the whole greenhouse, or going out.
Both generate considerable condensation [compared to electric], and both also rely on convection to get heat into the far flung corners of the greenhouse - an electric fan is obviously better at that. One counteracting approach is to put the heater under metal staging, which then heats the staging and thus the soil in the pots stood on it, which the plants appreciate (and often means they will tolerate lower temperatures at their leaves).
Either way, insulation is the cheapest form of "heating", so well worthwhile attending to that first - e.g. lining the structure with bubblewrap. Make sure that all air gaps are sealed with tape - you need to reduce all draughts as well as "double glazing" the structure. You could also look at keeping wind off the structure - a panel-fence, or hedge, around the greenhouse (but not close enough to shade it) will keep chilling wind off it.
Another trick is to erect a small polytunnel (like a very large cloche) inside the greenhouse, and only heat inside the tunnel. The greenhouse will provide the first line defence of keeping cold wind etc. off, and inside the tunnel will be a much smaller volume of air to heat.
But in a cold snap temperatures will fall, no matter how good the insulation is, and once the temperature falls you will be relying on the heating to stop the temperature falling further. To achieve that you need X-killowatts, so T-lights and so on won't be enough ... if we have a mild winter then very low numbers of Watts will be sufficient, in a perishinlg cold snap you'll need all the Killowatts you can throw at the problem.
My solution to the problem is to have substantial growing lights, in the house, and overwinter my plants there. I have sufficient light "power" that they continue to grow, rather than just ticking over, so I don't have to worry about moulds and rot and so on, let alone cold that could kill the plants.
-
I thought about buying a small electric heater for my greenhouse at home but actually it's going to cost me far more to hear it than any overwinter crop is actually worth. So bubble wrap & Growhouse in the greenhouse is the answer for me both on the allotment and at home. Terracotta pot and tea light at home only
-
Might be worth having some sort of temperature recorder (a Max/Min at least) so that you can judge how well the heating is performing (or, more correctly!, how low the temperature will fall on a cold night and thus what crops / plants you can keep alive / growing)
I have a couple of USB temperature loggers which I picked up cheap. They plug into my PC and I can "configure" them - basically how often I want them to log the temperature; they have a limit on the number of recordings they can store, so longer intervals between readings means a longer period of elapsed recording time (and the temperature doesn't gain, or lose, 1C in a short period of time, so once every 10 minutes is probably quite sufficient). Then carry to the greenhouse, press button for "START" and then retrieve them a week, or whatever, later and plug into PC and download the data then view it as a pretty graph :)
I also have some real-time wireless sensors, but they are only good for 50M max, and barely reach my greenhouse with direct line of sight from my home office window because there is a hedge in the way ... but they are handy to see the temperature in the greenhouse late at night without having to venture out into the cold night air :)
-
Lidl sell inside/ outside temperature gauges that record max and mins for the home and car for less than a £5 each and I have those in the greenhouses also have one that monitors the relative humidity bought for less than a £10 at a DIY store.
-
It was mentioned to me on this forum that you could make a hot bed in the greenhouse, or a pile of rotting manure piled in one corner with a sheet on it?
-
It was mentioned to me on this forum that you could make a hot bed in the greenhouse, or a pile of rotting manure piled in one corner with a sheet on it?
So you really want to be in there with rich manure :wacko:
-
It was mentioned to me on this forum that you could make a hot bed in the greenhouse, or a pile of rotting manure piled in one corner with a sheet on it?
So you really want to be in there with rich manure :wacko:
Don't knock it too much, I think it may just work!
It's an age-old process after all, we have a house down the road, with old greenhouses with six huge brick manure arches underneath! Apparently they heated the whole glazed area which was vast in present day standards!
-
It's an age-old process after all, we have a house down the road, with old greenhouses with six huge brick manure arches underneath! Apparently they heated the whole glazed area which was vast in present day standards!
I saw it, a while back!, on a BBC documentary called something like "The Victorian Kitchen Garden". Its probably on YouTube ... my recollection is that it was a phenomenal amount of manual labour digging the "spent" manure out, which had to be done [again, from memory] 3 or 4 times over the course of the winter as the fresh manure started to cool. I imagine they were only barrowing the spent manure a short distance to the rest of the, walled, kitchen garden, but it did seem to be a serious amount of hard work.
-
It can get very cold in Cambridge area in the winter, if it were me I'd bring the small trees home. Have you got a heated conservatory you could over winter them in?
-
They had the same system in lots of old gardens, they have one at Heligan. They used to grow pineapples using the same method. They still grow pineapples in the same glass house but I can't remember if it's heated with manure.
-
In the Victorian Kitchen Garden they used brick hot frames and put in three to four feet deep manure, then cover with another foot of regular soil, and cover with glass. The manure then heated up that frame as it breaks down, allowing for a self-heated cold frame to become a hot bed for start seeds and grow cold-hardy vegetables in even very cold weather.
Handy when you have a stable and a constant fresh supply of steaming hot horse poo - I was going to put a link to the second episode which showed them, but it looks like the BBC have had all copies removed from YouTube so glad a bought a copy from ebay
-
hi im a new member i have a greenhouse and have create a tent of bubblewrap inside it, i dont want to heat it i will use it just for protection from frost for some half hardy perenialls i have lifted from the garden what do you think is the max temprature i should aim for please
-
i will use it just for protection from frost for some half hardy perenialls i have lifted from the garden what do you think is the max temprature i should aim for please
16C ? I would ventilate on days when the sun is out once the temperature is over, say,10C. I would close the greenhouse early - at least 2 hours before sunset (bit of a guess, might be more) - to capture some heat to slow heat loss into the night (even if that raises the temperature to, say, 20C for a few hours)
If temperature doesn't look like rising above 16C then no need to ventilate for heat, but you still may need to ventilate to prevent moulds (or install a fan to circulate the air - that could be on a timer something like 15 minutes on and 45 minutes off (but I suspect you may not have electricity available in the greenhouse).
What I think you need to avoid is the plants making fresh soft growth until the Spring e.g. by the temperature in the greenhouse being toasty-warm. They will probably start early, February-ish, even if you try to keep the heat gain to a minimum, but you don't want them growing much / at all before that.
I would keep them fairly dry too - that will help with moulds, and without any/many leaves they won't be drinking much water anyway, and if their roots get soppy wet that may encourage rot.
-
Thank you that's very helpful I thought maybe 10-15c, I do have electric and a good min max digital thermometer but I don't want to spend more than it would cost to replace the plants on elec bills
-
I have been investigating information out there about the lowest temperatures that will keep things 'ticking over' (as opposed to what Kirsten does with his indoor grow-light system -- not jealous at all, you know :nowink:)
and it seems that 5deg C is perfectly adequate for pelargoniums and fuschias, and I already know that most citrus trees are hardy to just below zero anyway.
10-15degC is very warm, and would suit something like phalanopsis orchids perhaps.. if that is what you also have?
In response to the original query by ghost: you will have to gauge how likely it is that these minimum survival temperatures could be maintained in the early hours of along cold winter's night down at your plot.
Where we are, which is a valley bottom in a relatively mild part of the country, this would be impossible most years without some form of additional heating, regardless of any mechanical protection I could put in place. The pros and cons of a range of these have been given here already.
Personally I would consider bringing anything precious home. Our citrus trees survive each winter sitting on the kitchen floor by the large glass doors, and continue to flower and fruit.
I don't put them in our greenhouse because when the sowing season starts, it will be too warm for them in there, as I do heat it then to about 10 degC
Hope that helps a bit :D
-
If 5c is ok then that's v good I will just have to keep a check on the forecast thank you
-
If 5c is ok then that's v good I will just have to keep a check on the forecast thank you
If you have electricity in the greenhouse then I suggest getting a greenhouse fan heater (£20-30) and a quality thermostat (sadly that will cost you circa £50). The cheap thermostats that come with cheap heaters will have a huge temperature range between On and Off, so will cost a lot of money over-heating the greenhouse before the thermostat cuts out (or will underheat it and your plants will die :( ) then you don't need to worry about the odd cold night. You can also run the fan-only, no heat, periodically to move the air which has a dramatic effect on moulds, and doesn't cost much (compared to running the heater).
Cold winters, like 2010 but not like 1962!!, are usually only cold for brief periods so the cost of heat to maintain frost free is not usually significant, and then come spring if you want to start seedlings off early you can heat the greenhouse up more for a month or so (or put a smaller polytunnel within the greenhouse and just heat that)
-
You been looking in my greenhouse Kirsten? :lol:
That is exactly the kind of heater I have, and the cooler air fan feature is really good to clearing condensation from the inside of the bubble plastic when needed.
The heater is on the floor and my max-min thermometers at plant levels: those in pots on the floor and those on the staging, at both ends of the greenhouse, to try to ensure that there are no cold spots or those where the plants are getting to warm either come to that :nowink:
-
You been looking in my greenhouse Kirsten? :lol:
Drove by in Google Streetview for a peek :tongue2:
When I first got my heater I put a logging thermometer in the greenhouse to see how it behaved. It has a high accuracy thermostat and the temperature in the greenhouse (on a cold night) didn't vary by more than 0.5C
I don't have a cheap heater's thermostat to compare against, and its something that I've never found on Google that Which? or somesuch has done an experiment on, but I reckon that the hi/lo would be high (its not something that a Max/Min thermometer will capture, as it only records the absolute, not a single on/off cycle, although I suppose if it was reset on a cold night and checked an hour later, when the greenhouse would have been constantly needing heating cycles, that ought to give a good indication - at least, with that experiment, if the gap IS something huge like 10C it would indicate that it was worth investing in a better thermostat, and a gap of a degree or two is probably fine to leave well alone.
I wish horticulture students would come here asking WHAT to do projects on, rather than pitching up saying they've designed a new FORK and what do we think :( I have thousands of questions that need useful answers that only side-by-side tests can provide ...
-
I have thousands of questions that need useful answers that only side-by-side tests can provide ... (Kristen)
You are not alone ::)
-
thank you all for the advice i do have two small greenhouse heaters one was my father in laws but the settings are not helpful at all
-
Not even the On and Off? :unsure: :D
-
One doesn't even have that just one or two kl or numbers 1-5 :unsure:
-
1-5 is useless (but, sadly, common) on greenhouse heaters - you have to sit in the greenhouse on a cold night watching a thermometer until it falls to just the right point and then turn the heater dial until it just clicks on ... and then use a Max/Min thermometer to check that the range that it heats over is not huge / wild / over or under what you need.
Alternatively get an external highly accurate external thermostat and plug extension lead thingie, put the heater on full power, and plug it into the thermostat. Then you can just set the exact temperature that you want, which is much easier. They ain't cheap but if you heat your greenhouse a bit (e.g. frost free over winter, and then 10C in Spring) you should save the cost back in a couple of seasons by not over heating the greenhouse
Here's an example, suitable for heaters up to 3kW:
(http://www.jungleseeds.co.uk/contents/media/biogreenthermo1.jpg)
£39.95 from Jungle Seeds
http://www.jungleseeds.co.uk/contents/en-uk/d106.html#Product-P1565
Same thing £49.95 from Harrod Horticultural
http://www.harrodhorticultural.com/bio-green-digital-thermostat-pid9221.html
and £49.95 from Two Wests
http://www.twowests.co.uk/product/thermo-1-bio-green-digital-winter-thermostat
There is a slightly more expensive model which has an option to switch on either as temperature falls (for a heater) or rises (for a cooling fan in Summer)
-
I think that's just what I need thank you
-
Thanks again it's on its way :)
-
I think that's just what I need thank you
I bought the more expensive version about 3 years ago, because I wanted the heater in fan only mode during the summer. It has been in continual service ever since, heater in winter, fan in summer. Worth every penny as far as I'm concerned.
-
That's good to know Yorky thank you