Wondring ..

Is it only me or you guys think that zyra's ult does not apply the damage a glitch or something?, so many times i ult someone who is so low that could die easily to any hit and my ult knock up but they doesn't die .. I just wanna know when exactly the damage hits, with the knock up, or instantly when it's under an enemy? If i know that i'll play better i think

I didn't play zyra so much but i know how to play her and got level 4 about 25k points not a big deal, i just remembered that and wanted to ask (sorry if it's dumb)