If you're asking how to reduce the number of hours in a day that a plant is exposed to direct sunlight, then the answer is simple: shading. There are a number of ways to increase the shade on a plant. Planting other plants around it such as trees is a popular way. Planting them in particular spots such as next to the house or next to a fence is another one. One can also put up manufcatured screens and such which is an effective temporary solution but can be quite ugly and not good for the environment.