It's hot in Phoenix
 

I've brought in most of my orchids as it got hotter in the last two weeks. I'm bringing in most of the rest: Cymbidium seedlings, Ansellia, Dendrobium speciosum. Our nights will exceed 85 F/30C from last night through at least next week. It will be like this until our summer monsoon starts.

Many orchids use a form of metabolism in which they open their pores at night to absorb carbon dioxide. It's called crassulacean acid metabolism because the whole plant family Crassulaceae uses it: Adromischus, Aeonium, Crassula, Dudleya, Echeveria, Sedum, Sempervivum. Tillandsias use this metabolism, too. These are all difficult or impossible to grow outside here in summer. When nights are hot the pores don't open, and the plants suffocate. This is a big reason many orchids tolerate warmer days than you might expect if they can have cool nights.

The only orchid I know that easily tolerates our heat is Eulophia petersii, an African semi-desert terrestrial. But it won't take full sun all day. I haven't tried Catasetums outdoors in our heat, because humidity this time of year is in the 5%-15% range, and spider mites are established in our environment. Den. speciosum might tolerate this, but I'm not testing it this year.

Here is my Eulophia:

Attachment 146015

The empty pot is 3.5"/9cm diameter at the top, for scale.

You can see the weather forecast for my neighborhood at the link in my signature block.

Definitely not orchid weather! Yikes!

My Neem tree would love living there. :|

Where I live it has been around 104 F (40 C) during the day but it gets as low as 60 F (16 C) at night.
HR ranges betwwen 15 and 85%.
ES, do you have any info about the temp which the stomata starts to open? Or is it related with the temp differencial?
I'm asking this because I have some of my orchids always inside with temps of 25 F (24 C) but at night it doesn't change that much. I know they would benefit from being outside at night but I don't have the logistic conditions to do it.

Pore opening in crassulacean acid metabolism plants depends on light presence or absence, and absolute temperature. If it is dark and the temperature is correct, pores open. It doesn't require a day/night difference. My understanding is almost no crassulacean acid metabolism plants open pores at 30C/85 F and above. Many plants suffocate below this night temperature, however. It varies from species to species.

Can you open windows at night?

Do you mean higher than?
I've tried to let everything open at night but it doesn't change anything that much. The heat accumulated by the walls starts to be released at night into the house so it's like having heaters on. That's why temps don't change. Also, the absence of wind makes it more stagnant inside.

I meant lower. Many higher-elevation plants require much cooler nights than 30C to live. My point was that is close to the maximum for these plants, and it's too high for many.

I see...even below 30 C it's too high.
I must put some of my plants outside. They are acclimatized and growing well (after all, if I'm not mistaken, CAM process is an alternative one when conditions are favorable) but I want them to grow even better.

ES be safe with this crazy heat bubble. Sounds intolerable. Stay hydrated

Don't worry, DC. He's acclimatized!:biggrin: