Help Cannot find secret garden!

[Cigar and a Fedora]

Ahaha, I had the same problem... That's why I was asking for help on the Breeder's Discord to find it C: Well, there you go:

- Enter the Victory Road from Legen Town.
- There, in the sector with the tall grass you're in now, hold yourself as  south as possible.
- You'll shortly find a cave entrance, go in there.
- In that cave, there's a river leading north, follow it ti the end.
- Nearby is a cave exit. Go out, and welcome to Secret Garden.

An Elite Trainer couple with a team of Lv.72 Pokemon capable of megaevolving is there, defeat them to get the desired can. It will make your growing berrie plants all happy~

You need Waterfall don't you? 
I really wish the Wiki had told me that and saved me an hour of looking.