Let me first start off by saying this. Zyra is not a "support" she is a "MAGE" and as far as that goes, she can go in any lane that players want to play her in. What I want to focus on is the reason why she doesn't go midlane anymore.
Every since zyra's nerf to her passive long long ago (The old passive that allowed you to spit thorns on people after you died) People haven't really tried to play zyra mid. Recently I've been trying to bring it back, but I found a couple of problems that prevent me from making her a significant midlaner.
Issue 1. = Her passive
Her passive "~~Garden of Thorns~~" "Rampant growth" periodically spawns a seed that can be turned into a plant after using an ability on it. these seeds last 30 secs and dies when an ally steps on it.
Because you have 0 control over when and where the plants spawn, you are pretty much relying on rng on being in your favor. In a game like league of legends, macro is king. And being in the wrong place at the wrong time can kill you. Unlike the real rampant growth ( W ), your opponent can get a heads up on where you might spawn your plants. A smart enemy can purposefully position themselves out of the way, or even step on it when your shoved in, preventing you from making full use of your passive. In a support lane when your opponent is less worried about and more focused on melting your adc, you can get away with it. But for a mage, this ability is pretty underwhelming in all other matchups. The setup you need to make this work, is unbearable, especially in a matchup that might not go your way.
Issue 2. = Plants cant be controlled.
Zyra has 2 ways for her plants to attack. Either they attack the last target zyra is hitting. Or they attack a champion that is continuously in range, if zyra managed to land a hit on them.
This might seem like the biggest no brainer, but let me elaborate on why this is such a important feature to have on zyra. Most pets in game can be controlled by hitting Ctrl. For some reason zyra doesn't have this mechanic built in. Meaning if you want to hit a champion with your plants, you will have to either walk into auto attack range and start attacking them, or hit them with an ability. Now the later isn't so bad, but lets talk about the first one for a bit.
A mages auto attack range is laughable when compare it to there abilities. Zyra's range is 575. Her Q range is 800. Meaning if you want to hit someone with your plants, you would have to Q for almost 50%+ your range, walk up close to cover the distance, and then proceed to hit them in order for the plants to start attacking. Now if you play zyra, you will also know that her movement isn't great. So if you happen to miss even one of your abilities, your opponent can easily walk away from your plants, without taking any damage from the 1-2 that happened to spawn, and walk back 3secs later without trouble.
Now if your facing a melee champ in midlane, there is 0% chance in hell you would want to walk up to them in melee range just to activate a bonus 20 damage per plant. This along with the awkward positioning of your plants makes it almost impossible of effectively using your plants in lane Unless your really fed. Missing one ability makes your plants useless, and even when they hit, they die too fast.
Issue 3. = the damage
Zyra's scaling is average for a mage, but her base damage, if you can account for all the plants she can spawn, can = 100 damage per plant, up to a maxium of 8.
Now you are probably confused, as to why I am complaining about her damage being to high, if she is supposed to be a midlane mage. Well that's just the thing, her damage is high "OVERTIME" but for burst, it is actually on the weaker side of things. One of the major things I struggle with in the midlane is getting kills. My recent match on her showcase's this problem perfectly https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/3057603505/224885685?tab=stats
During the game, I am able to do a significant amount of damage to my opponents, but I am never able to secure the kills until after I die. My plants do a lot of damage, but not enough when it matters. By the end of the game, my ashe has 13/5/9. with the least amount of damage on the team, cause I died everytime in a teamfight, but always did the most damage. It felt like I was playing a support in the midlane, rather than playing a mage. If my team wasn't there to clean up for me, I would of been useless, even though I had the most pressure in the fights.
This also becomes increasingly frustrating when it comes to balancing, as it feels like a lot of skill expression is being punished just because she has high base damage on her plants. As I said before, alot of the game comes down to macro, and dying before your opponent, just because you couldnt get that extra plant hit off, can cost you alot of pressure in the late game. I don't mind her plants doing a good chunk of the work for her, but I rather that damage be more noticeable in fights while I'm still alive, not after the game is over and I check the scoreboard.
For one. I think a lot of zyra's midlane struggles come from the fact that her plants are unreliable. but I think being able to control them with solve a lot of these issues.
If her plants being controlled gives her too much power, you can simply give her 10% more scaling, bringing it up to 30%, and gut her base damage. I would argue that allowing good zyra players to express themselves by manipulating her own plants, will more than make up for her plants having a flat 20 damage rate with 30% ap scaling.
I know this sounds like a half assed solution, but if you have any better ideas on what can be added to make zyra a better midlaner, please share below. After all this is a dicussion