Unlike most of the US, in southern California, we have virtually no clouds in the summer months. When the seed package or directions on potted plants say, “Plant in Full Sun,” they’re thinking of somewhere other than southern CA.
My plants will start to wilt a bit on the hottest days, but they recover very rapidly as soon as the direct sun is off of them, around 3-4 p.m. Those plants exposed to 3-4 more hours of direct summer sun than my beds get, of course take more punishment, making it harder for them to recover. A lot of people make the mistake of seeing the plants wilt under the hot, direct sun, a nd water them automatically. And drown them. They usually don't need more water, just a little shade.
Lee O'Hara