Just, as someone who also plays Dota, there's this neato hero they ripped off called Venomancer. His Plague Wards deal fixed damage, don't scale, and don't eat spells. They're full controllable, too.
They grant experience and much higher equivalent gold, and for good reason. They're spammable wards, but they do far less than Zyra's do.
Zyra's plants should likewise not block spells, and should not have the ward style of multiple hits to kill. They should be a fixed HP that can be deleted instantly if enough damage is applied. If they stay the way they are, they should die to INSTANCES of damage, not 'hits' eg. Zoe passive counting as more than one attack, since it's a separate instance of damage delivered simultaneously.
They should also have a much lower AP ratio, given that their base damage is absurd combined with their very fast attack speed.
Just speaking from a pure numbers perspective on a champion that should be a lot more difficult to play for what level of power she brings to the field, rather than simply spawning a dozen mini-turrets that all proc her spell damage effects. Her E->R combo does way too much for it's overall utility, and the enrage mechanic is dumb for her plants.