You just can't get Cantlin Garden to work. You've checked tons of online content and it isn't working.

Chances are it's one of the following:

• Not enough water (you need 8 squares)
  
• Wrong kind of tree (has to be three squares tall)
  
• Not a room (it still has to have walls and a door like any other room)
  
• Not using a brazier (it's the pot-looking torch that sits on the floor...the same one as the top of the watchtower)

Above is a picture of a finished Cantlin Garden. Just to debunk some rumors: You do NOT have to build it in the town border. In fact, while it is possible to do (you have to basically build it underground because the only water source is like 4-5 squares down below the town), it's just easier to build it outside of town, and you can even do it in the swampy area that's nearby.

With your back to the prison front door (where you start), go forward until you reach the town outer wall/border, then hang a left and go straight; you'll run right into it.

The key is to find the right size tree. If your character looks like they could climb the tree, it's probably too small. If it has two layers of leaves, it's probably too big. Use the photo above to identify the perfect size tree; it's near the waterfront, you can't really miss it.

Then you'll need the shovel tool, which by the time you start working this quest you should have, but it's an optional tool, so you might not have it. You need it. OR you need the seedlings for the flowers; same as the grass. Either shovel them or get seedlings (which are dropped by drakees).

You need

• (5) Grass
  
• (10) Flowers (the white, yellow or pink)
  
• (1) Brazier
  
• (1) Bench
  
• (1) Bush (I used the medicinal leaf bush) << Users indicate that this may not be required despite multiple FAQs saying it is. See if it pops without it)

First, go into the water and dig DOWN. Make sure it's deep. This may or may not be required, but it may explain why some are having issues getting it to trigger outside of town (inside of town it'd already have been dug deep). You also need to make sure that 8 squares are inside the room you'll build, so make sure to reference the image above for what I mean.

Next, place your ornaments throughout, making sure to watch out for slimes that might get in the way. It doesn't matter how you place things, only that everything is accounted for.

It's a room, so you need the full walls and door. If one side is water, build a dirt bridge so that your wall is on solid ground.

If you've done it right, you should get the achievement popping up.