Making sure the water goes into the holes can be a bit tricky, so I decided to make funnels to make filling up the water easier.

There is a funnel for the square 28cm planter and a funnel for the square 22,5cm planter.

I have designed it so the water indicator can poke through and you can see how much water there is currently.

As always, the Fusion 360 files are attached, feel free to update and remix.