Temperature Woes in a Greenhouse in Spain

[flexy123]

Here my story so far...

We have a "cheap" small 6'x4' greenhouse here in Spain which we had on the balcony. There is very little sun (only in the morning), so I put the greenhouse on the sunroof which must be the probably sunniest place on this planet, BIG MISTAKE. I measured 117F (48C!!) in the greenhouse at noon, this with a fan going. (And yes I cut vents in the greenhouse too, but no effect really).

So we immediately put the greenhouse down at the balcony again which is basically always sort-of in the shade, and we got grow LED lights.

While there is no murderous sun anymore and I think the LEDs solved the light problem now, temps STILL can sometimes get pretty high, I mean this is Spain and right now we get to 38C (100F) around noon.

Humidity seems fine tho, between 35% and 50%, depending what time of the day.

I am still worried about the temps and really don't WANT to put an A/C in the greenhouse. (Utility costs here in Spain are outrageous).

I wonder whether 100F on exceptionally hot days like now can be a problem? I am asking since I see people grow in SoCal where it's hot as well and it seems not all strains have a problem with heat?

Really going crazy here, not much luck with groing anything here so far.

 

[iwltfum]

Some strains are better suited for the heat than others. Maybe you don't even need the greenhouse. From my understanding, greenhouses that utilize pots instead of the ground soil are built so that 1) The temperatures stay more constant at night, and 2) They trap the humidity making the greenhouse a more suitable space to grow (but this also increases temperatures). So if you already have the right temps and humidity outside, you might think about just putting them outside? And then, in the fall, when temps start to drop a little more at night, you can throw them back in the greenhouse to finish up in style. Just a thought. I've never grown in a greenhouse personally, but I have read up alot about the subject. And have plans drawn up to build a pretty big one some day.

EDIT: Keeping your roots (medium) moist on the hottest days will alleviate heat stress a bit. So will spraying them with plain water (that hasn't been treated with chloramine) , as long as they aren't too far along in bloom

 

[MrRudeSnowman]

as i recall superskunk did great in greenhouse under pretty extreme temperatures.

as for mixing LED and daylight... don't do it.

what you have to do is wait for plants to mature and then they will be able to survive the high temps.

mine was almost two moth old before going to greenhouse, still quite unhappy but grows like crazy too so i guess it's ok.

 

[JJ Bones]

You can always try to get yourself a shade cloth to see if it helps

 

[flexy123]

as i recall superskunk did great in greenhouse under pretty extreme temperatures.

as for mixing LED and daylight... don't do it.

what you have to do is wait for plants to mature and then they will be able to survive the high temps.

mine was almost two moth old before going to greenhouse, still quite unhappy but grows like crazy too so i guess it's ok.

Hi!
Can you elaborate why not mixing LEDs and daylight? There is (right now, at the balcony) very little direct sunlight (except a few minutes in the morning), this is why nothing was really growing before. I now set the timers 18hrs start 4am til 22h and thought that the added day light would be a good thing since the LEDs are not super strong, I have two normal, Marshydro "300W" lights in there.

You guys are right that "in principle" at least in Summer I wouldn't need a greenhouse - it's main purpose is really to keep the cats from the plants, no kidding! What I am gonna do now, I will cut even more large openings at the bottom/sides of the GH but put a wire mesh behind it.

The idea is to get as much moving/free air as possible but then with the option that I can close the vents in "Winter".

As for shades for the GH...at the balcony it is it's already VERY shaded, there is even a roof over it....hardly any direct sun light anyway this is why I got the LEDs.

 

[MrRudeSnowman]

You switch lights as less as you can, that's all. Usually we go from indoors to outdoors and that's when light change... or indoors switching from cold veg light to warmer one. Don't go from daylight to led to daylight to led, plants don't like that... that's all.

 

[Spain1]

You can always try to get yourself a shade cloth to see if it helps

Old thread but last year I put green shading over plants from noon until 5pm sitting on a wooden pallet as can't walk bare footed on balcony tiles ) still have 5 hours sunshine in morning and 5 hours after 5pm @ height of summer plus thin enough so still getting UV rays but not as powerful.....Putting the photoperiods in a plastic greenhouse this year ( as taping up all the windows so no light leak was a pain in the azz ) so I can open south facing fronts and has side and back meshing for airflow, guess will use fan or probably 2 ? as last year but going to put white reflective cloth over the top and under plastic roof. Can't do anything about possible wind burn but didn't seem to be a problem in 2023 my 1st ever grow when we had a week of 42 C !! Doing this not just because of taping up all windows but come croptober time which was still 30 degrees C, there were a few late summer proper pour downs so now will not have drenched buds. I'll let all know who have Med / So cali weather , the outcome