The larches were in my new cold frame against the East side of the house. It is fronted with a corrugated clear roofing material. They budded out early and had needles when I put them out in the cool spring weather, and they got direct sun. Mistake! That are generally has 50% shade cloth over it when it gets hotter. Nothing else was affected. Live and learn.
As I recall, you have a pretty dry climate correct?
Larch like moisture and as you found out, heat can be an issue.
I bought a larch in April that was collected from a bog in Northern Maine. I was concerned that an American larch might not adjust well to my heat. The seller told me that the bog does get rather hot in the summer and there isn't much shade. He is correct as I recall growing up in Maine, that yes it can get rather hot in summer.
However there is lots of moisture in the soil, and humidity being a bog. He said it should do fine as long as it gets a good cold period in winter.
I have had one larch for 5 years or so. Friend of mine has had some and early on had a lot of trouble keeping them alive while my one did fine
I have mine on a bench that gets morning sun and afternoon shade. My friend moved his to a similar spot I his yard and has had much better luck.
I have a lot more humidity than your area being that I am very close to the ocean here but I also keep mine in a soil mix that retains a more moisture than a typical conifer mix. They get watered every day in the summer.
If you are in a dryer climate, you are going to want then in soil that retains more moisture without being sopping wet and make sure they get watered often enough so that they don't dry out.
Hope this helps.