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greenhouse New greenhouse too hot and too cold.

Icablumoon

Icablumoon

I need some greenhouse advise. I just put up a hobby greenhouse (Easygrow) that is 6'x12'. It has a auto vent and a manual vent. When the temp's are in the low 60's and the sun is out it gets to be 105 even with the two vents open (they are both on the roof). It also has a manual vent near the floor but it also doesn't help. I have to open both front and back doors to cool it down so it doesn't damage the plants. At night it holds no heat from the daytime and then gets too cold. I have tried a heater with a built in temp. control but even though is goes on and off the temp stays the same as outside unless I turn it on high and turn the control up high and then it is using 1500watts. What am I doing wrong?
 
I know this isn't the answer you are going to want to hear, but the first problem is the greenhouse itself. I did research for two years before purchasing one and this is a common problem with hobby greenhouses. The 4mm polycarbonate has very little in the way of R-value, so keeping it warm at night is going to be difficult. Cooling it during the day is easier, buy an exhaust fan. It will require that you cut a hole in the poly, but it will work really well. My greenhouse can drop 15 degrees in 5 minutes when the exhaust fan kicks on. You can find a nice selection at www.farmtek.com and I would recommend a thermostat as well.

As for heating, seal EVERYTHING with clear caulk, the smallest gaps can negate any heater that you put out there. Get a 55 gallon barrel, paint it black, fill it with water and shove it in a corner. Or get two of them and put some boards across them and use them as a bench. The water is a thermal mass and will help hold a more constant temperature. Also, do you have the greenhouse sitting on a concrete pad or on the ground? Before putting up my greenhouse I dug out inches of dirt and filled it with 3/4" limestone. This provides drainage, and a bit of insulation from the cold ground underneath. The rock gets very warm during the day and stays warm through the night. Also, I put radiant barrier along the entire north side of the greenhouse that will be removed as soon as the night temps start staying above 50. This protects from cool northern winds sucking off heat from that side of the greenhouse.

I have spent the last 6 months constently improving the environmental conditions in my greenhouse. I am not saying I am an expert but I have come a long way from where I started.
 
You may also want to invest in some shade cloth to keep things cooler, and maybe throw a large blanket or tarp over the greenhouse at night for better insulation
 
Icablumoon, I'd be extremely interested in how your hobby greenhouse performs this springs and summer. I'm next door in Mississippi and this will be my first season with a hobby greenhouse too. I got the 7'x8' Rion Ecogrow. I found some foam insulation for window a/c units at Lowes and pushed that into all my gaps. The foam stays in place well...I was dreading the mess of squeezing silicon everywhere. My greenhouse seems to hold heat well through the night. I do have some thermal mass inside that helps retain heat...concrete pavers down the middle, drainage rock for the floor, and cinder blocks for the base of my shelving. My big worry is it getting too hot in the summer. Good luck to you.
 
Very nice information here, everyone so far except Potawie lives further south then i do, i live in Wisconsin wondering if it would even be a good idea to have a hobby greenhouse.
 
Here's a pic of my greenhouse...had her only 2 months and getting very attached. The polycarbonate panels on this model are a sandwich, kind of like clear cardboard.

greenhouse2.jpg
 
+ 1 on the fan and shade cloth for daytime temp. One other option for night time is to section off a smaller portion of the GH with some plastic sheeting. This depends on how much is in there of course, but if you can get by with a smaller area then the volume of air you have to heat is more managable.
 
I agree with the shade cloth idea. I just put 65% shade cloth over my pepper greenhouse at the end of last season and the plants have a perfect color to them. (which is the way I can tell they are happy) I don't know what temperatures you are dealing with, but my low last year was 16F for a short duration. Different things can work but that all depends on what your lows are, quality of the covering of the greenhouse material, and how well it is air shut once you close everything down. The black barrels are a good idea, but I found that they are not a for sure thing. Sometimes, we get about 3 days before a freezing event, that we get clouds and rain, which does not heat the barrels enough for them to work properly. What I did was bury most of the barrels in the ground and fill most of them with water and put tops on them. I cut holes in the top and in the sides at ground level, and the air moves through the barrels, is heated by the water, which is heated by the ground, and the hotter air rises up through the top hole. My 12 x 12 greenhouse was totally heated by just one barrel and I had no damage when it was 16F outside.
 
It seems I went from running my NG heater 12 hours a day to having to shade my greenhouse in about a 24 hour period this week. I have been working on ways to cool down temporarily until I am ready to put the shade cloth over the whole thing. I took the radiant barrier off of the north side walls thinking that it would allow more heat to escape during the day, but it had very little effect. I was still getting up to over 100 degrees in the afternoon with 75 degrees outside. Next I moved the radiant barriers to the south side walls, which kept it down to around 90. Finally, I moved the radiant barrier up far enough to be in the direct path of the Sun as it moves across the horizon, with the exhaust running the greenhouse is staying below 85 and everything in there is now happy.
 
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