@Protoavis
It makes sense that you would not be very concerned given the situation you have described above. ...
In my arid summer climate, the summer day temps are between 35 to 40C every day for about 4 months. That is hard on even established plants, unless you select plants that can survive in that kind of heat with low humidity.
I am lucky in that I live in the mountains where I have a 40 to 50F degree temperature change (4.5 - 10C) between day and night temps that allows the plants to rehydrate. However, this year was different. The temps did drop, but only for about two hours and the plants did not have sufficient time to rehydrate and were quite heat stressed.
A plant can have sufficient moisture in the root zone, but if it cannot pull moisture up to the top growth, the leaves cannot perform the function of photosynthesis and thus the plant is heat stressed to the point where survival becomes an issue.
You are correct in that it is vital that one of the best techniques for gardening in this kind of climate is to make sure that any plant has a larger root mass before it is placed in the ground. Young plants simply do not have the tools (roots) to survive in this kind of heat.
