As a big Zyra player, I dont think her plants needs bonus hp or damage.
They need to have a better AI, and they need to be more reliable.
Zyra's plants, when they grow, dont always start AA immediatly like they should do, but sometimes they stand still for 1-2 seconds doing nothing. This also sometimes happens when they change focus between different champions.
It's extremly annoying and I lose tons of poke because sometimes my plants decide to do nothing and they die without doing anything.
Also, buff that passive.