Donald ... that's a good question. We have a 40 to 50 degree temp swing between day temps and night temps. Day temps may be 100 F and night temps will be 50F.
In normal circumstances, cooling starts about an hour before dark and temps start to rise about 10 am, but that was really distorted this year, even tho' we had a wet year and a good snow pack. The temps started dropping after dark (9 pm .. still 90F +) and started rising just before dawn because our lake is at historical low levels due to the low lake levels. That is because of the insane California water politics that allow for an irrational water grab for central California. (I don't want to go into that here.)
This year, we had the low temps for only about two hours before they started rising again. This was a whole new gardening experience for me. Usually, the plants had time to recover from the lost of moisture through high transpiration rates during the high day temps during the night because of cooler night temps, but that didn't happen this year. My old mulching and watering practices really were quite inefficient. In other years, the plants had sufficient moisture in the root zones to pull moisture up to the top growth and were fine for the next hot day. Not this year. Even tho' the moisture was readily available for them, it was already HOT before the could move the moisture up to their top growth. Many of the plants were quite water stressed.
I don't know how long they are going to keep draining the lake, which has a significant impact on our climate, so I need to change how I mulch. I know that much, but I don't know what mulch material will be most economic and most effective.
I tested several materials this year and the combination of low humidity and heat is making the choice of mulch materials a problem, too. I've left a lot of space between my plants because I had planned to "fill in", but hadn't gotten that far with the garden and because I didn't want to plant while the drought was ongoing in my part of California for the last four years. The drought is over for my part of California, so I can think of planting again.
I've experimented with several mulch materials and am having a hard time finding what works in a hot and dry climate and still is a good weed inhibitor.
It's always something.
