-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 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 (a lot of them still focus heavily on the AP build despite the nerfs and the rework, or is centered too much around Deadman's Plate rush.)

-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 1/2 (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+ Inspiration is the most commonly used rune-set when building tank, and for a good reason.
Both help to mitigate the biggest issues Maokai has, survivability when engaging and early mana sustain.

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, 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 a bit.

From Inspiration we want to have Biscuit Delivery as Maokai runs out of mana early on rather quickly even with a conservative mana management.

For the 2nd option every minor rune outside of Magical Footwear has some merit to it. (As a support you wanna have boots early on to move around faster, and Mao also relies on MS a lot to be able to catch people with his W, as it's rather short range.)
I personally prefer Hextech Flashtraption as it gives me more flexibility at engaging/roaming, helps with warding over walls/ in enemy jgl, and there are a lot of situations where a fight transfers over terrain which Maokai can't follow by default unless he manages to catch someone with W.
If I were to opt for something else, it would probably be Cosmic Insight for more frequent flash/ignite usage.

Update 14.4: Currently not recommended!

As I mentioned in the notes, I only take this runepage vs double poke lanes. These are the likes of Lux/Senna/Brand/Xerath/Ashe...etc

While you still looking to all in onto these champions as you have good kill pressure once you unlock your W(+Q)+Ignite combo, Arcane Comet+ Scorch helps to relive some of the early pressure these double ranged lanes can put on you and your ADC, especially during lvl 1.

Eating one empowered Sapling does about 1/3 of the HP of these squishier champions when you run Comet, which increases your kill potential at lvl 2 a lot.

Since we run Manaflow Band as well, we can also spam our saplings more freely, even throwing at enemies not near the bushes.

The main thing to keep in mind with this Rune set is that we do sacrifice some survivability in the later stages of the game, so only opt for it if you are sure the lack of Aftershock won't hinder you in the bigger fights.

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.

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 2 main options that synergize well with Maokai:
- Celestial Opposition
- Solstice Sleigh

My primary choice is Celestial Opposition

The main reason is that the overall damage in the game is very high atm, so we appreciate anything that makes us more durable. It has a reasonably low CD compared to other items with similar effects, and it does an excellent job at mitigating front loaded burst.

Solstice Sleigh: With the latest buff to it in 14.4 (finally does meaningful healing as the game progresses), this item also became a good alternative. Vs poke heavy comps where Celestial Opposition would not have reasonable uptime, this item is probably preferred.
___
-Boots:
Boots of Swiftness is the most commonly built/optimal choice.
One reason is it's price, compared to the defensive options it costs 200g 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.

1st item:
With the removal of the Mythic system and the loss of Evenshroud, we are once again back to a Movement Speed oriented build. This time around Trailblazer takes the spotlight though as our primary item, compared to the previously used Dead Man's Plate.

While the later is still viable as an alternative, Trailblazer is 500g cheaper, and the stat difference is only 50HP, 5AR and 20MS between the two items. DMP also lost it's slowing effect, which can be pretty valuable vs mobile champions.

I do consider the team MS buff aspect of the item pretty underwhelming, but the cheaper price and the slowing effect still makes this item the preferable choice.

Unless we are playing against something like Ashe specifically, I would not consider going for Dead Man's Plate. (A newly added effect on the item is slow reduction.)
___

2nd item:
Since Trailblazer is purely an AR item, we will generally build an item with Magic Resist as our 2nd item. After reasonable playtesting in S14, I decided to pick Kaenic Rookern as our primary defensive option.
While I still think Abyssal Mask is a very strong item, Kaenic Rookern is just game-breakingly broken atm. The passive shield it offers just provides way better survivability, and with the damage creep in S14, it's something we really need.
Until Riot nerfs this item into the ground or just removes it, it overshadows the other options by a long shot.


On paper Force of Nature sounds very strong as well, but to proc it's passive, you need to tank for quite a while, so in general I prefer to have the magic shield instead, and would only opt for this item as a 2nd MR item.

___

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).

As we discussed our core items, which will basically be the "framework" of our builds in majority of our games, let's take a look at the situational items that possibly can fill the last remaining item slot we have.

Locket of the Iron Solari: Pre Evenshroud era this used to be the item to round out the DMP+Abyssal rush build, as this was the only Tank Support Mythic at the time. While the mythic system is gone, this item still remains a very good choice as a 3rd item.
It's very cheap, offers decent stats with mix resistances, and it also offers a reasonably strong AoE shield for you and your teammates around you.
If I don't need to opt for any of the anti-heal options, and don't need any of the situational defensive items (very high magic damage on enemy team, specific carry I need to survive against) then this is my go-to item.

Thornmail: Can be considered as an extra AR item as well vs very AA-reliant comps. Since the Grievous Wounds changes back in S13 it isn't that reliable as an anti-heal item, but still remains one of the strongest defensive options for it's price.
That being said, if the problematic healing champs rely a lot on their auto-attacks, then this is also your primary choice for anti-heal.

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 CC, 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 while Morellonomicon got a massive price reduction, we still don't want to finish the full item until we can't buy anything else. We only opt into this item for the anti-heal passive, and the 800g component already covers that.

____
Situational Defensive items:

Abyssal Mask: With Kaenic Rookern becoming our primary MR item, I am moving down Abyssal to 2ndary options. It's still a great item for it's price, Kaenic is just superior atm.

Force of Nature: This item is also very strong, but to proc it's passive it requires you to tank some dmg, so it's better as an additional MR item instead of a primary one.

Anathema's Chains: Strong defensive item when the enemy team doesn't have a well rounded comp (rely on a specific carry as their main damage). It's also good as a pseudo AR/MR item if the enemy team has only a single carry of a specific damage type.

____
Honorable mentions:

Randuin's Omen: This item became better as S13 progressed (stat increase, price decrease), but given that it's competing with Thornmail (+50HP -15AR) or Locket of the Iron Solari (+500g) it still remains super niche.

Knight's Vow: Item is cheap and got a reasonably good stat buff in exchange of the base HP regen, so on paper it should make a decent AR alternative.
The main reason I don't value this item is simply because Maokai mainly wants to throw himself into the enemy team in teamfights, so the passive won't be that useful, if anything it's counter-intuitive (makes us less tanky).
In a more peel-oriented/Warden-style Locket build it might still see some games.

Zeke's Convergence: Item has okay stats (although at the time you build it, you don't really need the extra mana) and it got it's old passive back, which makes the item slightly less niche. The items it's competing with though are simply better, so unless it gets some further buffs, it probably won't see many games on Maokai.

Frozen Heart: Very strong AR item, and it became support budget compatible in exhcange of 20 AR. The main issue is the lack of HP. Unless the enemy team is extremely AD heavy, it probably won't see many games on support.

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.

___
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.

E or W start?

-My general rule of thumb is that vs ranged supports (except Yuumi*) you should start with E.
The reason is, your E is the only thing that stops a ranged support from perma-harassing you and your ADC at lvl 1, and forcing you off the wave.
Without it, you can't really push for lvl 2 advantage using your support item ((unless you have a lane bully ADC, and enemy is weak at lvl 1)), which would be a mistake as lvl 2 vs ranged is one massive spike for Maokai.

-E start also helps you with placing a ward in the enemy jungle, to get info on the enemy Jungler's pathing. This information can dictate how aggressive you are allowed to play the lane early on, so it's very valuable.

-Generally if my team wants to invade at lvl 1, I tell them that I Need my E for the early lane, and I only agree to invade (W start), if I think we have the champs for it, and the enemy doesn't have many tools to counter us. Otherwise just ping them off from doing it.

*Vs Yuumi you should always start W. One reason is that your E is pretty useless against her, because she is sitting on the ADC. The other reason is, that once she detaches, you usually can surprise her with W start, and CC her for a good amount of dmg, especially that most of the time she will start Q, so won't have E to heal/mitigate it. W start into Q also allows for quick lvl 2 plays even against her ADC, which should secure you an early push.

-Vs melee both E and W has its merits.
E still helps with bush control, which can be useful vs catchers/hook champions.
W start means you get your W+Q combo quicker, and is usually preferred if you have the stronger ADC, to look for lvl 1-2 plays.

If you are unsure about a specific 2v2 matchup, you can always start E as a safe option, and wait for lvl 3 to get your full combo.

If the enemy has an aggressive ADC like Draven, Tristana, Kalista...etc paired with an engage/hook support, you probably better of playing it safe, and wait for lvl 3 with plays, unless you also have a strong ADC, in which case you should try to contest the lvl 2, but only if you are confident in your knowledge of the matchup, and in your execution. "It's better to be safe than sorry".

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.

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 on your 1st back, buy Boots and this is the latest time you should equip Oracle Lens. 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 before finishing Mythic, 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.

___
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.