Issue greenhouse shading

[Fohat85]

Dear growers,

I need your impression on the following problem.
In the last two months i lost several ariocarpus plants probably for the wrong shading cloth used.
I live in a particular spot (near ROME) where during the night the humidity/temperature in the greenhouse reaches 100%/20 °C and during the day around 25%/50 °C (summer - end june - early september).
In the last winter i replaced my green shading cloth (i dont know the exact shading %) with polypropylene black cloth with 50% of shade.
Unfortunately, as said above, every day i collect several "cooked" ariocarpus.

My questions are:
1st. why just the arios are dead? I'm collecting several species (mainly of middle america)
2nd. which is the correct % of shading second you for my situation?

Thank you

[MikeInOz]

The best shade colour to use is white (or sandstone colour) Black will absorb and radiate down more infra red light (heat). Light colours definitely are a bit cooler. I live in a climate similar to Rome (Coastal Victoria Australia) My plants are under plastic with a light covering to reduce the light a little bit (maybe 20% shade altogether) I don't get any burning on anything with that. The roof is high - 2-3 metres above the plants and I use a big fan too push out hot air in the summer. I have no idea why your Ariocarpus died but 100% humidity is very high. Why? Is the house enclosed or open? You need a lot of air movement all the time. 50C is too hot, the plants will stop growing and will not take up much water then , if any. Anything more than about 30 degrees at the roots will stop them growing and slowly start to kill them. If you water at that time the plants will rot. More shade and more air is what is needed at that time. If the sun hits the sides of the plastic pots the temperature inside will reach lethal levels very quickly. You can place the plastic pot inside a terra cotta pot to help with that. One more thing you can do is to cover the plants with tissue paper or heavy shade cloth cut into pieces and put them on the plants when the weather is crazy. Of course this is just general information.

[ohugal]

Rome is experiencing a massive heatwave, so it's not suprising you are experiencing issues with 'cooked' cacti. Is it just Ariocarpus you have issues with?
As MikeInOz mentioned, how well is your greenhouse ventilated? I have a very small greenhouse and as soon as temperatures go in the direction of 30°C I take out as much windows as possible, especially the roof. I have 2 thermometers, one at the level where the plants are and one higher up. The one higher up, closer to the roof, often indicates a temperature minimum +5°C warmer than the lower one. The temperature which triggers cacti into summer dormancy is not clear to me. MikeInOz says 30°C, but I thought it was +35°C in combination with night temperatures of +24°C.
MikeInOz's tip of a lighter colour of shade cloth makes sense. Also, if you can find shade cloth which is a combination PP and aluminium, it is worth trying. Aluminium helps keep the heat out more efficiently.

[MikeInOz]

Rome is experiencing a massive heatwave, so it's not suprising you are experiencing issues with 'cooked' cacti. Is it just Ariocarpus you have issues with?
As MikeInOz mentioned, how well is your greenhouse ventilated? I have a very small greenhouse and as soon as temperatures go in the direction of 30°C I take out as much windows as possible, especially the roof. I have 2 thermometers, one at the level where the plants are and one higher up. The one higher up, closer to the roof, often indicates a temperature minimum +5°C warmer than the lower one. The temperature which triggers cacti into summer dormancy is not clear to me. MikeInOz says 30°C, but I thought it was +35°C in combination with night temperatures of +24°C.
MikeInOz's tip of a lighter colour of shade cloth makes sense. Also, if you can find shade cloth which is a combination PP and aluminium, it is worth trying. Aluminium helps keep the heat out more efficiently.

Yes the top of the plants should be able to handle high temps but I was referring more to the temperature at the roots. Generally, roots temperatures in pots in summer are higher than habitat because they don't have the insulation and temperature stability of the ground.

[Hanazono]

Forum menbers live in various locations under different climates. My place is very hot dry summer and modelate wet winter.

My greenhouse has a roof and walls made by clear corrugated sheets. Since my collection is included Astrophytum and I want to control watering frequency by myself, a roof and walls are necessary.

50% white shadecloth is set in greenhouse. This shadecloth can reduce sunlight strength over cacti but can keep the room temperature as same as clear corrugated sheet because the shadecloth is set in the room. The room temperature reaches to 30 'C in the afternoon of a good sunshine day even if it was mid of winter.

The temperature of some day in summer exceeds 40 'C in here. The room temperature in greenhouse exceeds 50 'C easily if I kept the above condition. I cover greenhouse over by 50% green shadecloth from top for 4 months. This green shadecloth can reduce the room temperature and sunlight strength further. I tried to keep the room temperature within 50 'C.

Cacti need airflow. The greenhouse has doubel doors. One is corrugated sheet and the other is white shadecloth. The door of corrugated sheet is closed only in winter. Air can pass through the shadecloth door noamally.

Althogh the room temperature reaches to 50 'C, I have never experienced "cooked Ariocarpus". I can not stay long time in 50 'C greenhouse in summer but all Aricarpos seem all right. The humidity in greenhouse is around 20% in summer.

[Fohat85]

Thank you so much for your replies

Today morning at 10.30 AM i measured the lux of light outside (73k) and inside (26k) the green house reaching 44 °C.
The green house (pls see the pic) has unique entrance and two window side always opened.
There is no airflow, I'm going to add it right now.

next i should replace my black shading cloth with another green or white one
It also seems that some plants are getting sunburnt, a symptom of the wrong cloth (see pic).

[keith]

For sure Ariocarpus can sunburn but they can take extreme heat I used to live in Phoenix AZ they did fine under 50% shade cloth. These days where I live now I double my shadecloth in hot weather over certain species like Ariocarpus . Especially when fall comes and the sunlight comes in at a lower angle but still strong. All my big Ariocarpus are in clay pots I don't know if that makes a difference in root temperature ?

[Mrs.Green]

Just out of curiousity ( I have never grown cacti in a greenhouse) , under such conditions as described above, wouldn’t it be better to just have a roof of some sort with sunscreening? Then there would be no problems with stagnant air and overheating?

[C And D]

I have both black and white shade cloth in my green houses

I think I can offer an explanation
The Black shade cloth has larger holes in it, that allow some direct light through that may cook your plants
The white cloth has smaller holes, and it sometimes feels that a 50% white shade seems more shaded than 60% black

[Fohat85]

Just out of curiousity ( I have never grown cacti in a greenhouse) , under such conditions as described above, wouldn’t it be better to just have a roof of some sort with sunscreening? Then there would be no problems with stagnant air and overheating?

What do you mean by "roof of some sort with sunscreening"?

[7george]

Just out of curiousity ( I have never grown cacti in a greenhouse) , under such conditions as described above, wouldn’t it be better to just have a roof of some sort with sunscreening? Then there would be no problems with stagnant air and overheating?

What do you mean by "roof of some sort with sunscreening"?

For example I new some folks living in SE Europe that had been painted the whole roof of their GH with lime (white) permanently.

I guess your solution would be some active semiautomatic ventilation, like roof windows and fan(s) blowing air out in hot days. Have you measured temperature inside it? It could be reaching 60C or more if no active ventilation provided. That would reduce humidity as well.

[Fohat85]

Thanks, unfortunately I think your guess is correct.

I came back after 20 days from the holydays (august is the hotter month in Italy) and i found the plants very healthy.
Two days ago i watered my plants and after the third day some ario showed typical sign of "boiling".

I guess the high temperature (wrong shading cloth?) with water (maybe the wet soil reach high temperature) is the combo able to boil my arios.
Furthermore the whole opened greenhouse is no enough to airing the area.
Furthermore i discovered that the my black shading cloth i bought have 45% shading capacity (The seller told me it was 50%).

Maybe somebody can suggest me the best one?

https://www.artespolitecnica.it/2020/05 ... giante-50/