How hot is too hot?
 

I live in the Central Valley of CA. Our summers are HOT, We'll go weeks and never drop below 90 with multiple days over 100. A positive is that due to my location, the temperature drops an average 30-35 degrees F at night. In july, the average summer high in the low 90's, and the average july low is in the mid 50's. Summers are also incredibly dry. Frequent watering and a source of humidity would be a necessity I assume. I am wondering if the weather gets too hot outside for cattleyas, dendrobium nobile. I think my laelia anceps will do well outside, since I have read that it enjoys hot summers.

HI, Goodkoalie

I live in Georgia, with temperatures similar to your in summer, but higher humidity. We are nearly always in the 90s in the summer after mid day and before evening. Hottest I have experienced here has been 108 F, and my plants experienced no problems.

I can't answer about nobile dendrobiums (don't grow those). Cattleyas grow and flower just fine for me. Watering frequently will be important (you will want them to dry between watering, which should not be a problem in your climate). Be sure to provide adequate shade for them, especially on hot days.

My climate, more or less between late May and Late Sept is similar to yours in summer but lows on the mid 50's can happen but are not usual, usually are around high 60's/low 70's (frequently we have periods of weeks with nights on the low 80's).
Humidity gets as low as 15% and usually don't go over 30%, even at night.
I can't tell you about any specific genera (except Cymbs, which grow well) but I think if you water them frequently (once a day or every two days) and provide bright shade when needed, they will be ok.

A reliable drop at night can let you keep plants that might not tolerate lower maximum temps in a situation without a night time drop to the same levels you get.

Protect them from the midday sun if you have hot weather and keep them well watered. When we have hot summers, the Cattleyas grow very fast and I have found it beneficial to give mine extra Iron, magnesium and Calcium to help with stronger growth.

A lot of large Cattleya alliance plants should do fine with frequent water and protected from sun during the heat of the day. That nighttime temperature drop helps a lot. Still, small plants may simply dry out too fast. Deep shade if temps go above 100F with low humidity. And anything you can do to provide more humidity would be beneficial. A protected area with a fountain or periodic mist system maybe?

Many Den nobile hybrids will probably survive too, but I think low humidity would be even more of an issue. In any case, I'd try with a few tough plants before committing a large collection.

One more thing...if you're planning to move the plants inside when winter comes, remember low humidity is the parameter for pests like mites to develop.
Also, if temps and low HR are a serious issue, probably inside the conditions are more favourable.
I don't move anything outside 'cause inside is cooler than outside.

Many epiphytic orchids have the metabolism of succulents rather than mesic plants. This kind of metabolism does best with warm days and cool nights. Your temperature range will enable you to grow a lot of plants that normally don't prefer such high daytime temperatures.

You can raise the humidity by surrounding them with other heat-loving leafy plants that transpire a lot of water - corn, hibiscus, squash, gourds, pole beans, black-eyed peas, sweet potatoes. Your nights may be a little cool for okra to do well, but that is a great shade/humidity nurse plant.

With your low humidity your plants will be at risk of spider mite attack even outside for the summer. I would be surprised if they're not naturalized in your area. Be on constant lookout for them.

Thank you, everyone, for all the help. I think it may be best for me to keep my plants under my lights inside for now... Maybe if they are not happy inside I will try outside, although I do worry about spider mites.

It just occurred to me... Look up posts by WhiteRabbit (Sonya) who lives somewhere near Sacramento. She grows at least some orchids on her porch.