@Meddler: Should Zyra's ultimate do more for her plants than just increase their AS?

Zyra hasn't seen a lot of action lately due to her nerfs, but there's always been one thing about her kit that's irked me. Her plants, even with ulted, don't put out a lot of damage because they just die immediately to enemy fire. Since they die so fast, the bonus they get from Stranglethorns is pretty much moot point much of the time.

I think that Stranglethorns should give more than just bonus attack speed to Zyra's plants when it hits them. Maybe something like invulnerability (or at least better durability), more range, or some other effects. I'd lean most toward making the plants tougher to kill, though, so that they have better consistency in terms of actually doing something in a fight rather than just dying to AOE attacks or Immolation effects.