Walk in plastic greenhouse heating

Discussion in 'Greenhouse Growing' started by Ch3m, Apr 19, 2016.

  1. Ch3m

    Ch3m Apprentice Gardener

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    Quick question. I recently got a new walk in greenhouse the cheap plastic one. Tonight I decide to check the temperature inside it as well as outside. With great surprise I find out that there was no difference at all. Is that normal? I am a bit worried about the tomato and aubergine seedlings inside since here in Reading the temperature are around 10 degrees.
    I am planning to cover the north part of the greenhouse with bubble wrap since it doesn't get any light due to the fence. Could this improve the situation? Any other solutions?
    Thanks
     
  2. CanadianLori

    CanadianLori Total Gardener

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    Sorry for the bad news but other than supplying overnight heat or having large masses such as barrels of water which have been warmed by the daytime temps and sun, you will have no difference between in and out temperatures.

    Trust me, I live in Canada and tried bubble wrap, etc but without adding an after sunset heat source, there is no gain.

    As you get closer to the last frost, then the greenhouse can help by acting as a giant cloche. Which is good, right?

    I have two small plastic ones which I will enjoy using it's shelving throughout the summer sans plastic after the last frost. Zero sedlings go in there until the overnight lows are over 40f. I have two small polycarbonate greenhouses and lots of sleepless nights worrying to offer as my credibility
     
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    • JWK

      JWK Gardener

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      I have a small blow away right next to the house facing South, it stays at about 1 deg C above ambient over-night. During the day if the sun comes out the temp soars unless I open the flaps, I've recorded 48C last weekend - far too hot for plants. I only use it to harden plants off over-night.
       
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      • Ch3m

        Ch3m Apprentice Gardener

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        Thanks for the info. A friend of mine told me that the temperature in her polytunnel are normally 5 degree higher than outside so I thought the reason in my case was due to the low quality of the purchase since I got the greenhouse form wilko for 25£.:snorky:

        For now I don't think the cold would be much of a problem but for the future it might be. Do you think a paraffin heater or a candle under a terracotta vase might be helpful in the future?
         
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        • JWK

          JWK Gardener

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          That might be true during the day, certainly in my glass greenhouses it gets much warmer. But overnight it's a different story, even in my glass greenhouse without any other insulation the temp is practically the same as ambient, the only benefit it cuts out the wind chill factor and any moisture so plants do survive better in there than being left outside.

          I gave up on paraffin as it gives off moisture when burning and raises humidity encouraging fungal diseases. The easiest option is a fan heater on a decent thermostat, costs me about £30 over winter to keep my bubble wrap insulated greenhouse just frost free, but of course you need the electric supply to be safe and professionally installed which could be prohibitive

          Anything will help, it's worth a try - you may have to partition of a smaller section with plastic to contain the heat.
           
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          • clanless

            clanless Total Gardener

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            Nothing wrong with them - I have one and am very pleased with it :blue thumb:. As JWK says they do provide a level of protection.

            Even Monty uses heaters in his big posh greenhouses.

            Just remember to keep the front open in hot weather :SUNsmile:- they are greenhouses not hothouses:spinning:.
             
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            • CanadianLori

              CanadianLori Total Gardener

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              I have a natural gas heater in my 6x8 greenhouse and I have insulated it with window film.

              The smaller 6x4 greenhouse is where I use kerosene/parrafin lanterns. Yes, those metal old fashioned ones. They keep the overnight temperature approximately 8f above outdoor/ambient. This wards off freezing/frosts.

              The plastic greenhouses are as @JWK says are really very good for hardening things off and then make great displays when you remove the plastic. I won't be moving plants into these until around the middle of May.
               
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              • CreakyJoints

                CreakyJoints Gardener

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                Hi @Ch3m , I have one of the walk-in mini greenhouse. I also have a 4 tier mini growhouse and a bigger walk-in mini greenhouse. I haven't tried the biggest one yet, but have both overwintered and grown plants from seed in the other 2.
                These are the ones I have -
                http://www.coopersofstortford.co.uk/coopers-of-stortford-4-tier-grow-house-prodst08043i/

                http://www.coopersofstortford.co.uk/coopers-of-stortford-the-stortford-grow-house-prodst07705i/

                I used the fleece frost cover, underneath the plastic cover, on both of these over the colder months.

                Last spring, I tried using a tealight & terracotta pot heater in the walk-in growhouse and managed to keep it frost free overnight on even the coldest nights.
                Instead of a tealight though, I used long burning pillar candles so that I didn't have to go out every few hours during the night to replace the candle.
                Here are some photos showing how I set this up,DSCF8121.JPG
                First of all, both growhouses were tied very securely to my fence with polypropylene rope. They stayed in place during the strongest, gusty winds (up to 60mph gusts at times).
                You can see the fleece covers underneath the plastic covers here. On milder winter days, I opened up the zips on the plastic covers but left the fleece covers closed.
                Once we were into spring, I moved the plants out of the 4 tier growhouse, removed both covers then using cable ties, I secured the 4 tier frame and shelving inside the bigger growhouse to give me more space for trays of seedlings.

                These next photos show how I set up my pot & candle heater in the bigger growhouse.

                1. I sunk a terracotta pot into the soil for stability, sat a heavy glass candle holder in the bottom of the pot, then placed the candle into the candle holder. This candle was a 50 hour pillar candle from Tesco. The pot & candle were positioned in front of the shelving so that it wasn't directly underneath the seed trays.2013-10-09 01.28.13.jpg

                2. Next, I placed a rack over the pot & candle (stainless steel rack I found in my shed - it was the rack from an old grill pan. The legs are stainless steel pins you use to hold down weed control fabric. I used wire to secure the legs to the rack.). With the legs pushed into the soil, I positioned the rack just above the wick of the candle. Doing it this way, the rack could be lowered by pushing the legs further into the ground as the candle burned down. I then lit the candle before placing the next terracotta pot onto the rack.
                2013-10-09 01.29.01.jpg

                3. Next, after plugging the hole with foil, (to trap the heat), I placed a small terracotta pot upside down on the rack, directly above the burning candle.2013-10-09 01.29.17.jpg

                4. Next, I placed a bigger terracotta pot over the first one. The heat trapped inside the smaller pot heats this bigger pot, which in turn, allows warm air to heat the growhouse.2013-10-09 01.30.05.jpg

                5.2013-10-09 01.30.26.jpg

                6.2013-10-09 01.30.35.jpg

                The pot & candle heater did produce soot as well as heat though. I had to wash down the inside of the fleece cover a few times to stop any soot build up from blocking out light.
                It worked, but was messy. I'm in an upstairs maisonette though (and have...ahem...not very well behaved childern in the maisonette below mine) so couldn't run an electricity supply out to my garden. If I could, I'd have an electric greenhouse heater outside instead of this. :)
                 
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                • Scrungee

                  Scrungee Well known for it

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                  Heat retention overnight depends a lot on the volume of a plastic covered greenhouse/tunnel. I have two 2 x 4.25m polytunnels (one of which is about to come down) and two 3 x 6m polytunnels (one of which is about to be erected).

                  The smaller tunnel is bigger than a 'blow-away' greenhouse and on a frosty/freezing night the temperature will go down to the around outside temperature, despite closing the door and vents earlier than usual so it heats up a bit in advance of dropping overnight temperatures. Minimum temperatures in the larger tunnel will be a couple of degrees or so higher than in the smaller version.

                  Around dawn is usually when temperatures drop to their lowest, so any non-thermostatic form of heating used to maintain a minimum temperature from evening to the following morning will be burning loads of fuel unnecessarily for much of that time.

                  And shortly after temps have dropped to their lowest point, they'll start rising and unless you're up in time to turn any (non-thermostatically controlled) heating off, temps will soar inside [1]. Many a time I've closed a small tunnel up and worried about overnight minimums, and it's been > 90 deg F by the time I've opened it up in the morning, plus got a second shock when I've checked a max/min thermometer and seen what's in been down to.

                  Temperatures were so awfully low during late May/early June last year that I spent a lot of time bringing plants back from polytunnels, stacking them in crates in our living room & greenhouse overnight, then monitoring outside temps to check when they could all be spread around our garden, but I had to ventilate the tunnels well in advance of putting stuff at home outside.
                   
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                  • CanadianLori

                    CanadianLori Total Gardener

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                    So, I guess we are all saying that no matter how we try to handle these heating issues, we all get lots of exercise ! :heehee:
                     
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                    • Ch3m

                      Ch3m Apprentice Gardener

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                      Got the message. I will give up when frost will come. Meanwhile I thought to use the old 4 tier greenhouse inside the walk in for the seedling. Could that be a good idea?
                       
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                      • Scrungee

                        Scrungee Well known for it

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                        My understanding is that some plants will always be damaged by frost, but not necessarily by the same temperatures without an actual frost forming on their leaves (it's when it melts that causes the damage).

                        I've got one of those (from Wilkos when reduced to 1p) and will check out whether there's much temperature difference inside it when sited in a pollytunnel or simply inside the tunnel.
                         
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                        • CreakyJoints

                          CreakyJoints Gardener

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                          If you look at the photos I posted above, that's my 4 tier growhouse inside my walk-in growhouse. The 4 tier fits nicely at the back, between the shelves of the bigger walk-in. I took the cover off the 4 tier one though and cable tied it to the frame of the bigger walk-in. That way it didn't topple over inside the bigger walk-in when we had very strong, gusty winds.
                          I check the local weather forecast on a site called accuweather. I've found it to be very accurate here. You just need to type in your town or postcode to get the weather forecast for your own area. :)
                           
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                          • HarryS

                            HarryS Eternally Optimistic Gardener

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                            How do you do it ! :biggrin:
                            Just a word on paraffin heaters . I used a Parasene heater for 10 years , without a problem . I bought a new one - same model , and it won't stay alight all night ! Now a paraffin heater is not exactly high tech - a wick in paraffin ,adjusted to the right burn height . I sent an email to Parasene complaining , and they don't have the decency to reply . One company to avoid .:nonofinger:
                             
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                            • Scrungee

                              Scrungee Well known for it

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                              I've just checked that site out.

                              I live in a village where verified overnight minimums are normally around 2 to 3deg C lower than forecasts for my nearest town, and they are a further 2deg C or so lower at my edge of village plot. Most weather sites simply repeat exactly the same temperature forecasts for the nearest town when postcode/location name searching for a forecast.

                              Accuweather does the same, OK maybe for towns, but there's no adjustment for the lower temps in rural areas from my check a few minutes ago, so they could be around 5 degrees out with their forecasts for where I grow. That sort of inaccuracy means I could lose everything planted out or even in polytunnels.
                               
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                                Last edited: Apr 19, 2016
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