-About me: I am a Maokai Support (near)OTP who plays under the alias - FunnyBunnyH in the EUW server. I picked up the game in S10 and over these few years I accumulated a few 1000s SoloQ games on the Mighty Tree as a support, while climbing to Diamond/Master rank.

-The reason for this guide:
When I was browsing for support specific Maokai guides, I couldn't really find a really in-depth guide that is also up-to-date.

-Why Maokai support:
Maokai in my opinion is probably the best all-rounder tank support in the game. He has a ton of CC, great both as an engage- or peel support, amazing at establishing vision thanks to his saplings, and his kit is overall very well suited for objective centered metas (the ones we have in recent years).

-Pros:

Strong CC/utility (suitable for any comp)

Good Vision Control

Easy to execute kit (beginner friendly)

Strong Scaling (dmg and survivability)

Is a flex-pick (less counterpicking)

Good synergy with almost any lane partner

Not many hard matchups/counterpicks

Not often picked/banned

-Cons:

weak lvl 1(certain 2v2 matchups can be difficult early game)

low influence in games where your team is behind
(if your team lacks damage, your engages don't really work)

Requires a stronger matchup knowledge than traditional Tank supports
(Maokai's early sustain is weak and he doesn't have dmg mitigation in his kit so you need to be more thoughtful of your engages in lane)

Resolve is the most commonly used primary rune-tree when building tank, and for a good reason.

Maokai unlike traditional tank supports, doesn't have any damage mitigation in his kit, so he heavily relies on the extra resistances Aftershock provides, especially when engaging against multiple opponents. You also have good "sticking power" with your kit, so you can reliably land the damage part of the keystone as well.

From the 2nd row neither rune is really amazing, but overall Font of Life is the most reliable choice. Demolish is an okay rune if you have a favourable bot 2v2 matchup, but you can't really know for sure if you get the chance to proc it in lane, and it's value is somewhat limited once the plates are gone.

3rd row all options are decent, Bone Plating is useful at every phase of the game, but if you have a lane where you are not really under a threat of dying, you might wanna opt for Conditioning. With damage creeping up again as we start off S14, I personally started to default to Conditioning for better survivabilty in teamfights. Vs aggro ADC picks ( Draven, Samira, Kalista) Bone Plating might still be required. Second Wind is usually picked vs double poke, but your passive and the two pots should be enough sustain early if you are not eating every skillshot/letting your opponents constantly aa you, so I would still opt for the other two in those matchups.

From last row after 14.2 I would default to Overgrowth. Unflinching extra resistances are pretty negligible, and at the time it offers reasonable stats, Overgrowth should have already outscaled it. Revitalize is an okay alternative as it helps with your FoL healing and potential Shielding with Locket of the Iron Solari, it also affects your passive healing.

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2ndary runes are more flexible, and usually come down to playstyle/preferrances. In this part I will explain what your options are and what the benefits of each are.

- Inspiration: With the nerf to Biscuit Delivery (doesn't provide mana anymore), this 2ndary tree became slightly less appealing on 14.19. Hextech Flashtraption and Cosmic Insight still offer reasonably good value, so if you don't mind the lack of mana, it's still a decent choice.

- Sorcery: With MS systems getting nerfed in 14.19 and the initial MS nerf to Maokai in S14, this rune tree became even more appealing IMO.

Manaflow Band for the mana sustain and Celerity for it's extra movement speed. This rune helps to offset the initial base MS nerf to Maokai, and the %MS scales really well with Boots of Swiftness or any of the Winged Moonplate items.
Opting for Celerity also makes you less bound to MS oriented items (less trade-off for buying Armor/MR boots or rushing Locket instead of Trailblazer 1st item...etc), so in a sense it offers a bit more flexibility with your builds.

For those who don't care about having mana in runes Nimbus Cloak is also a very strong MS rune that helps a lot with both engaging and disengaging.

-Honorable mention - Domination: As far as I seen, this rune-tree is mainly picked for Relentless Hunter, but in my opinion Celerity is just a better MS rune. Relentless Hunter is only active out of combat, and you also need to stack it up, while Celerity is active from the start of the game.

The other rune options in this tree aren't that valuable either compared to what Inspiration/Sorcery has to offer.

By default you should pick Flash and Ignite.

One great thing about Maokai support is that he offers insane kill-pressure in lane once he unlocks both his Q + W, and Ignite dmg is usually a difference maker between being able to burst down an enemy or not. It also helps vs any healing they might have with an utility support or Heal summoner.

Exhaust is generally taken with teamfights/later stages in mind, when you have a specific assassin/dmg threat you want to shut down, or when Ignite doesn't provide much value outside of lane (generally vs tankier comps).

Since Maokai generally doesn't have very one sided 2v2 bot matchups (and even in those you can "fish" for openings), you generally want to keep your chances of securing early kills in lane, this is why Ignite is taken as the preferred summoner.

-Starting item:
With 14.1 rolling out, World Atlas became the only choice for starting item. Once completed, you have 3 options that synergize well with Maokai:
- Solstice Sleigh
- Celestial Opposition
- Bloodsong

Solstice Sleigh: Overall the most "universally good" option out of the 3 as it will always provide value. It's useful both in a peel oriented build (ms+heal for the carry you are trying to proctect) and in an engage oritented one (ms to help allies catch up to you).

Celestial Opposition: Bit situational, but does an excellent job at mitigating front loaded burst. The 2 seconds slow on it is also very valuable, helps with escaping after getting caught or ensures that you can catch up to opponents after your initial engage even if they flash away. The main drawback of the item is that it does somewhat poorly vs poke (easy to proc it). Generally build it with engage oriented builds or vs "pick comps".

Bloodsong: Also situational, but pretty underrated. It's good in games where opponents have a lot of sustain, as it helps bursting down enemies you manage to catch out. I generally build it vs utility supports, or when the opposing team has a lot of champs with in-built healing in their kit.
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-Boots:
Boots of Swiftness is the most commonly built/optimal choice.
One reason is it's price, compared to the defensive options it costs 200/300g less, which might not look like a lot, but on support budget every gold counts.

Another reason is that while Maokai has great target lockdown and sticking power with his kit, he can struggle to get the initial engage going, because his W is rather short range. The extra MS helps a lot in this regard.

And one last reason is that our Sapling's MS does scale with our own MS, so it buffs our E slightly.

Defensive options like Mercury's Treads or Plated Steelcaps are taken only in very specific situations (Ton of CC on enemy's side,(multiple) high AA-based dmg threats), and even in those cases you want to consider if the extra defense/tenacity is worth sacrificing your mobility.

Honorable mention: Symbiotic Soles - These Boots are tied for being the cheapest at 900g and having a shorter recall is certainly very valuable, but without the upgrade they only provide +35ms and it actually takes a reasonably long time to upgrade it. Also pretty much only worth it if you are rushing tier2 boots, which reduces your build flexiblity and makes you a lot squishier early game.

-Our 1st item will be determined by our main role in teamfights.

Locket of the Iron Solari: If you have an ADC you really need to protect (something like a Jinx/ Kog'Maw/ Aphelios (but could be an important carry in other roles as well), or if the enemy team is very dive heavy, you generally want to rush this item.
The AoE shield it provides helps to keep your teammates alive and you generally don't mind the lack of MS on the item because in these games the opponents will look to jump on you and your teammates anyway (opposed to you trying to jump on them).

Trailblazer: If you have a more utility based carry ( Jhin/ Miss Fortune/ Ziggs...etc) that doesn't rely on peel that much or you have other champions in your comp that can help keeping your backline alive, you want to build this item, as it helps to engage onto enemies easier thanks to the MS it provides.

If you happen to snowball in the early game you can opt for Dead Man's Plate instead for an extra 500g (it provides an extra 100HP and 15AR and also offers a bit of extra burst at your initial engage).

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-Our 2nd/3rd item will mainly depend on what we need the most (anti-heal, more AR or MR).

Kaenic Rookern: This item is by far the strongest MR item in the game RN, while being reasonably affordable even for supports. Even the base stats on it are very good at mitigating magic damage, but combined with the magic shield it provides, it makes you very hard to deal with for pretty much any AP champion.
The Spectre's Cowl component also recieved a buff to it, which improved its build path.

Thornmail: Very strong AR item vs AA reliant champions. In 14.19 it lost 200HP but gained 15AR and it's price was also lowered to 2450g. With the slightly awkward build path it doesn't feel as good to rush as a 1st item anymore (only has a single Ruby Crystal worth of HP which makes you rather squishy), but it's a very good 2ndary AR item for it's cheap price, especially if you need the anti-heal part of it.

Randuin's Omen: Pretty competitive with Thornmail. It has stronger components, and it also provides +200HP while only having -5AR for an extra 250g.
Overall this item is the stronger of the two when it comes to late game, especially if you don't really need anti-heal or if the enemy team has multiple crit-based carries.

( Thornmail is still preferred vs champions such as Smolder/ Ezreal or any other carry that doesn't really build crit).

Note: With Trailblazer/ Dead Man's Plate 1st item you generally will want to build MR for 2nd item, as both of those items are purely AR items.

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Last item:
We will round out our build with Vigilant Wardstone most of the times. Main reason is because having Control Wards on us even in late game is super valuable. That being said, the item actually became even more appealing on 14.1, because it offers some mix resistances now instead of bonus AP/AD (stats we didn't really need/use).

Oblivion Orb: Vs champions that don't rely on aa-s to proc their healing ( Kayn/ Vladimir/ Fiddlesticks are main examples, but it's also very good into healing supports since their target won't necessarily aa you).
Since Thornmail lost it's passive which gave anti-heal based on your CCm Oblivion Orb became the more reliable option for Grievous Wounds. This item applies anti-heal on your entire kit for just 800g. The downside is that it makes you somewhat more squishy as neither the component nor the finished item offers any defensive stats.
Also important to note that we don't want to finish the full item until we can't really buy anything else. We only opt into this item for the anti-heal passive, and the 800g component already covers that.

Knight's Vow:Good AR item with a peel oriented (Locket rush) playstyle to keep your main carry alive. For engage oriented builds I don't recommend it, as it just makes you squishier.

Abyssal Mask: If you don't need Kaenic Rookern to survive in teamfights, then this is an okay alternative, but with losing roughly 25MR and getting a price increase as well on 14.19, it might just be too niche to consider on support atm. (After all, you can also opt for Locket/Merc's for MR in those games).

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Honorable mention- Zeke's Convergence: It's cheap, it offers decent stats for it's price, and has +100HP compared to Locket. The main issue, is that it's passive is pretty useless on Maokai, and it can't really compete with the 1st item options (better passives), or the defensive ones (better durability).

Note: This part has been not updated on 14.1, as the notes I wrote to the freshly added champions in the preview section should have enough information. When I get some time for it, I will include them in more detail here.

-Matchups:
As you probably noticed, I didn't include many of them, and most of them aren't even supports.

One of the greatest thing about Maokai support is that unlike other, traditional engage supports, he doesn't really struggle in isolated 2v2 matchups because he does have a ranged ability despite being melee.

In melee vs melee matchup you basically go toe-to toe vs all except Blitzcrank*, and the dynamic of the early fighting is usually decided by who has the more dominant ADC and who secures lvl 2 1st. Even if a champion like Leona/ Nautilus/ Alistar is slightly stronger than you in lane, both your sustain and your DPS massively outscales them as the game goes on, which gives you an overall edge against them.

*(Blitz hook can isolate either you or your ADC in an 1v2, but even this matchup is favourable for you overall if you have both W+Q unlocked, depends ofc on the ADC picks).

In ranged matchups you can keep the enemy out of bushes with your E (Which makes their poke more dodge-able both for you and your ADC) and if you can secure the lvl 2 advantage (generally you should because of the support item difference), you can try for a quick all in onto one of them with W+Ignite, especially if they are already chunked a bit by your Saplings.

As I mentioned earlier, Taric is the only "official" Maokai counter. He pretty much does the same you do in lane, except his sustain is superior, and he even shares it with his ADC, so it's very hard to win out on trades, if the enemy duo doesn't misplay.
The only advantage Mao has over Taric is that he is better at ganking other lanes because Taric's CC is very situational/hard to coordinate with randoms.
In teamfights his ult basically shuts down your ult/engage, so you either burst your target before his ult charges up, or you have to wait out the 2.5s invulneribility, which is a rather big window for them to kill you and your teammates.
Luckily Taric is a very unpopular pick even above Plat+, so you won't play this matchup often, and when you do, you always have the option to dodge as well.

With the rise in popularity of Heimerdinger(the only reason you are allowed to hate on DRX), Maokai players were quickly reminded how annoying this champion is regardless of which lane you meet him.
Unlike other poke supports, you can't really scare him out of bushes, because your Saplings target the closest enemy to them, which are his turrets and not him, and it takes quite a few E-s from you to actually take them down, so you are generally better not bothering with them and just play towards the river side of the lane. Your best bet is to survive lane without feeding (he is annyoing, but doesn't do that much dmg if you don't get stunned by his grenade), and be more useful at roaming/teamfighting than him. Side note - this is one lane where you might consider taking Comet over Aftershock.

Caitlyn is one of the few ADCs which can force you and your ADC to play more passive at earliest lvls. While you have your E to counterpoke her and her support, it does have a relatively high CD, something Caitlyn'S autoattacks don't have.
If you make it to lvl 3 without getting chunked down too much, you can try to punish them with W+Q+Ignite, as both she and the ranged support she is usually paired with is rather squishy.
You generally do well vs the likes of Lux/ Morgana at later stages because of their squishyness and how well you scale, so overall these matchups aren't that bad for you outside of the earliest lvls.

Draven pretty much wins 1v1 in lane against any ADC because of his insane early dmg, so these lanes you are kind of forced to play passive early on regardless of the support matchup, but it's especially true vs another melee/engage/hook support, as they give Draven even more kill pressure.
You scale very well though, so if you don't feed him in lane too much, he won't be an issue at later stages of the game.

Samira/ Nilah overall very strong(S+ Tier) champions currently. Lane you might secure a lead, even a few kills, but one misplay is enough by your team during mid game, and they snowball out of control. Samira with her relatively high PR is ban worthy champ. Nilah sees less gameplay overall, but can be just as problematic to deal with.

Sivir Boring, perma-wave clear champion with a spell shield. If she and her support plays it safe, there isn't much you can do in lane, so try to roam and secure early objectives/kills elsewhere so she doesn't have an opportunity to scale into late game.

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Regarding synergies, Maokai is pretty much playable with all ADCs and even APCs, because he is very good both as engage and as a "Warden-like" peel support.
The only exceptions are probably Senna (You can't really farm for her) and Aphelios (he is rather weak early, and not many players are adept at playing him).

This and the fact that he doesn't really have terrible matchups makes him a very good/safe Blind pick overall.

14.4 Update regarding starting ability: Start Q/W. Q is the more standard, W is good for invade/lvl 1 bush plays. E CD is too high currently, so lvl it up 3rd.

Your basic combo is W onto enemy champ, Q towards your ADC (to separate the support and ADC) and ignite them. This usually secures a kill vs most champions, especially if they weren't full HP to begin with. (You can AA after Q/ignite if they still in your range, Aftershock dmg also should go off in time, but the important part is to get the Q direction off properly and in time - your W is a very short CC, so Q has to be pretty quick). Not very hard to learn, 5 mins in Practice Tool should do the trick.

(One thing to note: If enemy ADC has Cleanse, getting this combo off is much harder, assuming they use it properly, so be more thoughtful of your engage in lanes like this.)

Once you have your entire W+Q combo and have Ignite available, there aren't many champions that you don't have kill pressure on with the help of your ADC, but it's especially true vs ranged/squishier supports.

Unless the wave is very close to their tower or you/your ADC is very low, you should always at least consider an all in.
When you have Flash available as well, you can engage from even further, and if you took my advice and equipped Hextech Flashtraption, you can be more "liberal" with your standard Flash usage, as Hexflash from bushes still allows for you to engage from range.
The only drawback of not having Flash up, is you are more easy to gank by the enemy jungler, but since you have your E for vision, this isn't an issue most of the times.

To have more successful engages from the lane bushes, you should get Oracle Lens either by backing until 0:55 after you placed your 1st ward (this still gives you time to help with leashing your jungler if they need it) , or after your 1st back.
This will also help in case you want to make a quick gank attempt at mid after your 1st back.

This is not "Maokai-exlusive" but buy Boots on your 1st back. This will unlock your roaming potential to some extent, also helps to rotate faster between lanes/objectives.

Ideally you want Boots, Ruby Crystal, Control Ward at your 1st back, but as long as you get Boots, you are fine.

I generally get Boots of Swiftness (or tier 2 boots) before finishing my 1st item, it helps with better roams/rotation.

Maokai is very good at objective control once he hits lvl 6 because of his ult and saplings, so if your team isn't behind, you should generally look to secure early objectives with your jungler.

Use your saplings to check bushes, and use this to place deep wards in enemy jungle when you have some time to roam.

Maokai makes a great Warden with his Q(knockback ability), always play him according to what your team needs the most (engage/peel).

Since Maokai is a 3 role-flex pick, you can fake hover champions from Jgl/Top lane, to pretend you are picking for one of those roles. This sometimes can help to secure a favourable matchup for your teammates, who otherwise would not get the counterpicking opportunity.

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Hope you find this guide somewhat useful, if you have any questions/feedback feel free to reach out to me in DM/Comment.

GL on the Rift, FunnyBunnyH.