Zyra Feedback - Unifying her infester theme and placing her in a more zone-control oriented role.
I'll make this brief. Most of you are already aware of the problems with Zyra. She has a passive that doesn't mesh with her kit, her W is very boring to rank, her ultimate's secondary effect is virtually unnoticed, she tends to be extremely oppressive to lane against (and difficult to balance) due to high harass and CC, and her plants generally seem like added damage rather than a core component of her kit.
Proposal:
Change the passive to be her seed mechanic. Seeds would sprout in an area around her at a steady rate and wilt/despawn when she left a certain range of them. The intent is that she would slowly be building a nest of seedling around her the longer she remains in an area, making her a defensive oriented support and a dangerous person to engage on if she is able to occupy an area long enough, much like other zone control champions such as Illaoi or Heimer.
Make her Q into a knockback, similar to Vel'koz's E so that she can force an enemy onto an area of control to line up her abilities and make use of the randomly placed seedlings. The ability could still create the shooter.
Turn her W into a new ability, preferably defensive oriented for her support role, and grant her a new plant. This gives her an alternative ability worth ranking up in her support role, besides for more damage. Like her other abilities, this should turn nearby seedlings into that type of plant. Perhaps a shield?
Make her E into a one second root, but rather than having her seedling spawn a vine lasher, let seedlings hit by it erupt into an AOE that will snare surrounding units in a small area (rather than a line) for extra damage, with the eruption potentially offering a longer duration if you're able to land it.
Since her kit now has the obvious weakness of reducing her ability to quickly relocate, turn her R, "Rampant Growth", into a primarily damage oriented ability that will quickly spawn many seeds in an area, allowing her to easily follow up with the rest of her spells to chain her seed effects. Since she now has the knockup on Q, I don't think she needs it on Growth anymore, since the damage and seed spawning would be enough. Maybe offer a slowing effect to keep people within the area for a bit. This lets her create her zone of dominance at the cost of her ultimate, much like how Illaoi gains her tentacles upon activation of her ultimate.
Anyway, it's just a potential direction to take Zyra rather than keeping her kit mostly the same. It gives her a unique playstyle centered around getting your enemies to position near your seedlings and turning her from a snare/burst mage into a more defensive zone control mage. Rather than dropping seedlings and spamming your E to harass and snare people, you would have to be carefully analyzing your positioning relative to the enemies and their proximity to your seedlings so that you can "set up" your chain. It also makes an immobile mage a threat to just jump on, while simultaneously reducing her ability to aggressively zone and harass (the problematic parts of her kit that make her hard to balance).