Hello again! I know this is a pretty general question, but I have been looking around quite a bit and haven't found any info about these trees in a similar environment to mine. I also seem to read some conflicting info so I'm hoping some of you with experience with these trees can help.

I live in Southern California zone 9b. I am on the out skirts of what we call our lower desert but at a higher elevation. I am located at about 2700 ft (820m), my summer temps average around 90-95 (32-35 C) but can reach as high as 110f (43 C) on hot days. Winter can be cold (for a Californian lol) and as low as 28f (-2 c) but we typically don't get any real snow. We get a light dusting of snow flurries maybe once or twice a year but nothing that would require a shovel. My yard has a range of full shade to full afternoon sun so I have some placement options for my trees. I have read that JBP will tolerate 110 degrees as long as their pots are deep enough. I also read that they do not need a full winter dormancy. I purchased a bunch of young trees, all about 8-12 inches (20-30cm) tall and have them in the recommended soil mixture (combination of pearlite, peat, pumice, decomposed granite, bark, compost and soil) given to me by the vendor and growing in 6" pots. I plan on keeping them in this soil mixture and growing naturally for probably another year or 2. They seem to be growing quite fast at the moment. I have placed them all around the yard, some in full sun, some in only afternoon sun and some in mostly shade to protect them from the heat. The full sun even as the days reach 90+ degrees (32 c) does not seem to bother them at all.
I talked briefly with an experienced bonsai grower at a class I took a few weeks ago. He mentioned that he has had trouble with JBP trees and currently is not growing any. He did not give me a real reason why and our conversation got cut short so I wasn't able to get clarification. I'm wondering what may be some of the issues I may run in to? Does this environment seem like it should allow these trees to thrive? Is there something I am missing? I am reading more and more on these trees and learning lots but sometimes much of the info comes from very different growing conditions and I want to try and compare apples to apples.

Many people around here keep there trees in heated greenhouses in winter. 5 c is the most common temperature and I can assure you yhat works good as winter dormancy.

Your summer heat may be a problem the hottest days. It may make sence to protect them then.

Humidity is what I think is your biggest challenge. All japanese species like high humidity in summer.

Thank you for your response. It is very dry where I live. I do water the lawn daily which raises the humidity in the yard until the sun dries it all out late morning/early afternoon. Would you recommend a humidity tray for them or is that not enough?
I also have both a shed and a garage I can protect them in during the coldest nights. I do have a greenhouse but it is kept hot during the winter so that would not allow it to go dormant. I've read that they are fine in temps well below freezing but then I also read to protect them once it gets to freezing temps which is why I ask.

My black pines is outdoors all year and I live in Sweden. The ones planted in ground get no protection. The ones in pot is in unheated greenhouse. Winter 2020-2021 it was well below minus 10 day and night for 6 weeks and it was no problem.

Your challenge is not cold winter but hot and dry summer.

It is not possible to control humidity locally outdoors. In order to increase humidity you need a contained space.

I would not expect many troubles so go out and ask your local grower what challenges he faces.

I do not believe Japanese Black Pines need high humidity. They are susceptable to foliar fungi so drier would be better normally.