what's a good support vs. a zyra support at bot lane?

Nunu.

Delicious.

A Zyra support is difficult cause of her strengths. She has a good AA range and tons of harass potential with her abilities. She can ward bushes with her seed pods and has a great root/snare with her e and a wide aoe knock up in her ult. Her passive can be effective after she dies to help secure kills for her ADC even.

This being said her cons are that she is mana dependant and blue buff probably isn't going to her anytime soon and she won't be able to build a chalice relatively soon unless the team agrees to help buy wards. She's also incredibly squishy.

So you can either try to counter by playing safer champs like caitlyn and lulu or you could be more aggressive and go for champs like draven leona or graves thresh combos. I prefer aggressive combinations because I can get in her face which is where she doesn't want to be.

Soraka. Zyra has very little hard cc to prevent Soraka from healing, and Soraka's passive helps against Zyra poke. Starcall also lets Soraka kill plants very quickly.

There are a few things that work very well against Zyra as a support.

1. Mobility

2. Range

3. CC

Zyra is very very dependent on landing her E, Grasping Roots. The reason that Mobility counters her is that if you never get rooted, she can't properly full on engage you and she isn't nearly as useful in lane as she could be. As long as you can avoid getting nailed by her root you'll be fine.

The reason range counters her is because of how slow her E is. Since it got nerfed, it's a lot easier to dodge, and if the support playing against her has high ranges themselves they never need to get close and get rooted and all-inned. Champions like Lux or Nidalee can poke from high range without getting nailed.

CC counters her because she is squishy and very reliant on being an active part of the fight. Before she gets any health a high CC champion like Blitzcrank can effectively CC her long enough for him and the ADC to bring her down before she can do much of anything. However this can be risky because if you don't kill her early before she can get items like a sightstone to become tanky, she'll still get her full spell combo off even after being gripped and the fight can easily go in the Zyra's favor.

All in all the best way to fight her is to make sure she can't do what she needs to do, root and all-in you. So play champions that can keep her at range and never let her in close enough to mess you up.

nami suprisingly.
morgana

Anyone who can hard engage. Leona or Taric wreck her pretty easily. Especially now that her E projectile speed is lowered.

I like picking Lux, and then its a battle of annoying snare mages.

Morgana is amazing aganist her, Black shield is a huge counter to he abilities