Mini-Greenhouse Upgrade and Question

Hello all! I recently purchased one of those basic mini-greenhouses - the ones that are just a shelf unit with a simple cover. I got it as a temp solution until I can build a larger greenhouse in a year or two. I don't have room in my house for the plants I want to start. But I quickly found that the temperature would jump dramatically if there was even a little sun - almost cooked a few of my first starts! The cover has a door but it opens from the bottom and I can't let the hot air out at the top without opening the whole door. I tried adding some large concrete blocks and large bottles filled with water to function as thermal mass but that was not enough. So I recently added two vents on the top of the greenhouse. The vents are manually opened and are kept closed or opened by using simple magnetic latches - the "hinge" of the vents is made using velcro so I can remove the vent covers if needed. I got the material for the vent covers for 89 cents at Goodwill and it was higher quality material than the cover that came with the greenhouse. I'm now just waiting to see how effective the vents are at keeping the day time temps at a good level but I need a sunny day first.

Have any of you all used this type of greenhouse? What has been your experience and how did you deal with the rapid changes in temperatures that a small greenhouse tends to have?

Nice chop job! Ive actually sortof abandoned (what looks like) the exact same type of GH. Bought it and used it to mostly kill everything inside any day I didnt show up and just leave it fully open. I never found a spot that didnt turn it into an oven with 30 mins of sunlight, but I found a use using it like an upstanding cold frame. I have a house at the bottom of my a garden which is north facing and a (hilariously badly planned) severe frost trap. I pretty much left it open any day that didnt freeze, but when it would Id close it and over-winter mature plants inside. Meh!

I think youve inspired me to PIMP MY GREENHOUSE.
Lettuce know how yours pans out!

Ian Rule wrote:Nice chop job! Ive actually sortof abandoned (what looks like) the exact same type of GH. Bought it and used it to mostly kill everything inside any day I didnt show up and just leave it fully open. I never found a spot that didnt turn it into an oven with 30 mins of sunlight, but I found a use using it like an upstanding cold frame. I have a house at the bottom of my a garden which is north facing and a (hilariously badly planned) severe frost trap. I pretty much left it open any day that didnt freeze, but when it would Id close it and over-winter mature plants inside. Meh!

I think youve inspired me to PIMP MY GREENHOUSE.
Lettuce know how yours pans out!

lol, ya I was very close to cooking some of my first plants and have not had any in there after that happened. Before the vents were added the temperature peaked at 109 F - I'm hoping that one vent opened will be enough to keep the temperature at around 60 to 70 F. I want to try opening the vent when I leave for work in the morning and then closing it when I return or soon after depending on how much sun I'm getting.

I will post an update once I have a sunny day to test it out!

Do you have open flaps on the bottom walls? That should help greatly with cooling via air pressure circulation.

Amy Escobar wrote:Do you have open flaps on the bottom walls? That should help greatly with cooling via air pressure circulation.

I did not make new flaps but the door opens from the bottom so I can open it a bit to let some air in. Thanks for the suggestion! I had not thought about that.

Hi, adding containers of water will keep daytime temps down a bit and then slowly release that energy overnight and keep the temperatures up. Watch out for round bottles unless the liquid is coloured or they can act as magnifying lenses and burn the plants.
See here for some more details.
Using water to maintain even temperatures in greenhouses.  Appears in Growing Green International Issue 33
http://www.what-is-permaculture.co.uk/articles-by-tony