Giant cactus only spawns every so often, and when it is killed, does not come back right away. I think it is on 2 hour spawn, not sure exactly. What is more, one of the three types of it spawn, and as per Murphy's law, never the one you really need.
Back when DDC was populated a lot, you would usually see "Giant Flower is up" zone shouts. These days not so much.
Of course, it always helps to be sure to be at the right spot too.
-- Rustyx --- 92R / 92S / 92M on Reni (Guild KnightShift). Yes, running the new FOTM R/M, cause I am not elf enough to be WD/S.
Oh, and people who have more than 3 classes are clinically insane.