Why plant branches turning red?

[crysstlalyzed]

Why my plant bottom branches turning red? And leaves turning yelow and some of them just fall off?

 

[Conradino23]

Some sativa varieties will be doing exactly that when in flowering, but you might've some nutrient issue. Depends on what you're growing.

 

[Stealthboat]

Pictures would help immensely here.

 

[SparkNShred]

Some sativa varieties will be doing exactly that when in flowering, but you might've some nutrient issue. Depends on what you're growing.

Also depends on what stage of growth it's at. If it's outdoors and in the Northern Hemisphere, it's perfectly normal, as the plant nears the end of its life.