The point of this guide is solely to show the cookie cutter build order very easily. I am not going to go into any advanced tech or strats on how to win more. It's just something to follow while you try to improve.
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PROS + can solo win lane + good dps output in late + strong utility + can solo carry + can take farm IF no one else will take it

CONS - immobile - every spellcast stops your movement - mistakes are easily abused - squishy

Poke with Q Deadly Spines if you hit it and autos on level one. You don't want to waste any mana here.
At level 2 you can start trading with Q Deadly Spines -> W Rampant Growth -> auto combos.
Only use E Grasping Roots to disengage or when you have lethal. General All-in combo is E Grasping Roots -> W Rampant Growth -> Q Deadly Spines -> W Rampant Growth and then of course autos afterwards. Sometimes you can start the combo with Q Deadly Spines -> W Rampant Growth if you can't hit your E Grasping Roots yet. This can either put them in a position that makes it easier for you to hit your E Grasping Roots afterwards or you just poke them down more so you're lane is more free.

After hitting level 6 you can generally just always all in the enemy if you hit your E so the general combo would be E Grasping Roots -> W Rampant Growth -> R Stranglethorns -> Q Deadly Spines -> W Rampant Growth
Again you can start this with Q Deadly Spines -> W Rampant Growth and then follow up with the start of the combo for the same reasons. You always want to prefer poking the enemy if landing the engage isn't safe.

This is the phase where you want to stop poking the enemies with Q Deadly Spines -> W Rampant Growth combos. This is not only because of you not being able to auto safely and therefore not being able to focus the plant on a target if you don't hit Q Deadly Spines but also because you want to always have your plants available as soon as an actual fight breaks out so you can maximize your dmg output.

So what you do is poking the enemy solely with Q Deadly Spines and not placing any plants. You can use the seeds from your passive Garden of Thorns if they sit comfortably tho.
When teamfights happen you just rely on your All-in combos that you already used in the lane phase.

If the enemy dives on you and you can't hit a safe E it can also make sense to start your combo with R Stranglethorns -> E Grasping Roots -> W Rampant Growth -> Q Deadly Spines -> W Rampant Growth or even go R Stranglethorns -> E Grasping Roots -> 2x W Rampant Growth -> Q Deadly Spines if you only need to make it hard for the enemy to move because your team will just kill them if they don't get away or if you don't expect to survive long enough to put out a Q Deadly Spines -> W Rampant Growth before dying.

Q Deadly Spines - standard poking tool, that's it

W Rampant Growth - creating two kinds of plants, Q plant Thorn Spitter having range, E plant Vine Lasher being a slow, it's the main dps tool, so you want to place the plants so that they dont just die together and kind of zone the enemies in a way that you get the maximum damage out put, you also want to mix both types of plants because otherwise the damage of at least one plant is reduced due to balancing. You can also place seeds in brushes or behind walls to gain small vision, so you don't have to facecheck when warding.(If you need or want to read on those two kinds of plants you can go to this link and scroll down to the pets section.

E Grasping Roots - great cc, good disengage, good counterengage, mostly a reactive spell due to how slow it is and because it stops your movement making you a lot more vulnerable if you fail it. Rylai's Crystal Scepter can help you to find engages because you can slow with Q Deadly Spines and/or Thorn Spitter (optimally both because you want to maximize damage) beforehand.

R Stranglethorns - strong burst, good combo tool, input buffer, if your teammate aoe cc's the enemy team and you aren't quite in range you can press R Stranglethorns under the enemy team and then flash afterwards and do your combo. The spell will activate instantly. You can also put it under enemies affected by Zhonya's Hourglass or Bard's R Tempered Fate at literally any time and the burst will always come out at the very moment they get out of the stasis as long as the initial damage delay already passed, you can't miss dealing the damage.

Passive Garden of Thorns - Works the same as your W Rampant Growth but isn't as reliable. You need to be outside of a brush for 2 seconds before your passive plants seeds. Your passive won't plant any seeds in your own base for the first 5 minutes of the game. When leashing you want to start planting seeds at the timer 1:00 so you will have the maximum amount of your Q plant Thorn Spitter.

A lot of people buy Liandry's Torment before Rylai's Crystal Scepter however the best of the Zyra players go Rylai's Crystal Scepter first. It gives you a lot more utility, it already allows you to 100-0 the enemy without them being able to escape, it allows you to get more Arcane Comet procs because your plants will get more attacks (specifically the Q plant Thornspitter), it allows you to find an easier engage, it makes it easier for you to stall.

The only reason to go Liandry's Torment first is if you have to win through poking the enemy down or the the enemy won't be able to escape from your combos anyway.

classic skin, it's fine

does nothing

does nothing

does nothing

It's a bit of a cheater skin because seeds are a bit harder to see but it's not nearly as much of a cheater skin as iBlitzcrank for example, if you have the money and want to have it easier you can chose to play this skin but don't expect to win more because of this skin.

16/08/2020 - Changed comet as a keystone for aery because comet is extremely easy to dodge and you almost never proc it with your cc ability so the keystone isnt reliable, also with Zyras AA range and low Q cd it's extremely easy to have aery on a permanent cooldown which results in aery dealing a lot more damage, even if the enemy doesnt consistently dodge comet.