Greenhouse vs Cold Room / Cold Frame by Dave Bogan

Some consider them all about the same. Actually there are big differences, mainly heat, light, and your intentions. Dave sheds light on the differences.(0512)

I live in an apartment in a city with a short growing season.

To cope I built an above ground grow-box to house my small collection of shohin and medium sized bonsai. It's by no means an ideal growing situation but it has been largely successful. To deal with our cold winters I've built a thermostatically controlled space heater into the box and it works like a dream (luckily my power bill is included in my criminally high rent).

I've attached a couple of pics for your consideration. The burlap in the corner is for shade to keep my JMs from scorching. I built it from my imagination with no guides so if it looks a little dodgy, well it's because I'm no carpenter. That said, if you have any ideas on how I might improve the design please feel free to give me some pointers.

Thanks,
Jeremy

I have a greenhouse I would like to use as a coldframe, what should I do to ensure it doesn't heat up too much during the spring? I've got shade cloth 60%, automatic louver opener, bottom vents and a wireless thermometer that send the temperature inside for me to see and monitor.

I mulched all my trees in the front flower bed last spring which worked well but doesn't let me work on them easily and requires a lot of garden space. With 20 trees now thats a big mulching task I'd rather avoid.

EK,
leave the door open like in your picture and get a fan near that door blowing out

Dave brings up some excellent points in his article wrt cold frames, especially the point of rising internal temperatures of cold frames during sunny days. I never had a problem with my cold frame the first year. It overwintered my trees quite well. The 2nd and 3rd year I had top damage as Dave explained, and subsequently lost several trees. Some were damaged beyond repair some were saved and some could not be saved.



In order to progress one needs to find out what happened to cause the trees demise. The first year I had applied shade cloth to the underside of the top panel. I omitted the shade cloth during the 2nd winter (most of my damage occurred that year). My 3rd year I once again used shade cloth, all went well for the winter. Because of abnormally cold spring (read early) I removed the shade cloth and once again got caught with my pants down. Although sufficient aeration was available several trees got their tops scorched once again. That year I was vigilant but this can occur with just one day. Remembering what had transpired the year before, I decided to bring all my trees out to the bench. All went well with the exception of major restyling required on the damage trees. My blog has an excerpt wrt this.

I had a "pop up" greenhouse made of white tarp-like material that was used for my conifers. UV got the best of that so I decided to build a greenhouse. Considering what was transpiring during spring and that the old greenhouse was not clear, I decided to use 65% shading glass vice clear when I built my greenhouse. Unlike Dave I do not heat mine nor do I do starter plants and my trops are kept inside during winter (too expensive to heat a greenhouse, just fot trops)

This past spring when buds started to dwell I moved all the trees that were in the cold frame to the greenhouse, everything went well. As a matter of fact better than expected. The trees took of like a bat out of hell. Mind you this was my 1st year doing this and was hesitant in bringing my trees out to the bench since they were under UV protection, so to speak. Now I had a dilemma and I was worried. Because my bench has partial shade and the temps is Nova Scotia are relatively mild I decided it was worth a gamble and all went well, no trees missed a beat (knock on wood). My conifers on the other hand were all moved outside when the deciduous were brought into the greenhouse. My rationale is that they spent the winter outside relatively speaking and it was safe to do so. All went well with them as well.


The gable ends of the green house are aluminium screen. Surprisingly enough no snow found its way into the greenhouse last winter. The gable ends face the predominant winds in my area. I have kept other plans in there during the summer and sufficient ventilation exist, even during the hottest months. This is where I over summer my cactus and jades. One needs to watch these closely for water, but other than that, I think I have finally found a solution that works for me.