One simple change to make Zyra viable mid without breaking her bot

Make it so her plants execute minions they hit under certain HP threshold.

Since you need your spells to hit the champion for plants to focus them and since Zyra's spells are extremely unreliable, plants often fuck up your CSing and there are more than enough situations where that might make you miss the entire wave because mage basic attacks (bla blah Karthus, irrelevant to the problem).

We can help her mid a little by this without having any impact on support role except maybe lowering her obnoxious poke, because it would force Zyra "support" players to not summon plants just for zoning, knowing they would take alot of ADC's CS.