What is considered 'ground you can see' as target of a spell like Create Bonfire? Can it be ground overgrown by plants after casting Plant Growth

Question

What is considered 'ground you can see' as target of a spell like the cantrip Create Bonfire? For example, can you see and thus target ground in:

• an area overgrown by 1' of dense grass (you don't see the ground anymore)
• an area overgrown by 3' of dense grass/roots/shrubs (you don't see the ground anymore)
• a room littered with broken furniture and wood (you don't see the floor anymore).

Update: In question/awnser What is "the ground"? it seems more or less agreed upon that ground is 'whatever solid surface the characters and monsters are standing on'. This does not 100% answer my question: you stand on the ground below the grass/bushes, so if the grass is dense, you actually do not see the ground the enemy is standing on. My interpterion of RAW is you could not. But the RAI might allow it?

Concrete case

Being charged by a Troll, our druid cast the 3rd level spell Plant growth (on a grassy & grassy hill with some shrubs), using the option to:

"All normal plants in a 100-foot radius centered on that point become thick and overgrown. A creature moving through the area must spend 4 feet of movement for every 1 foot it moves."

After downing the troll 40' away, we wanted to finish it by casting the cantrip Create Bonfire:

"You create a bonfire on ground that you can see within range. Until the spell ends, the magic bonfire fills a 5-foot cube."

Our DM suggested the ground would no longer be visible, as it is overgrown with thick plants. So we could not see it clearly, thus we could not target it with Create Bonfire. What would the rules say here?

Answer 1

When you're able to see the square you're casting on, and it's a ground square.

5e, outside of a few specifically defined terms, tends to use natural English meanings for words. As such, I don't think that there's an official rule of how to adjudicate this, but here's how I'd do it:

If you're able to draw a line of sight between yourself and the target square (or point between four squares, if an effect that radiates out from a point rather than a cube), and that square has the ground as one of its faces, then you're able to target it with the spell.

So, if there's dense underbrush, but you can still see the square, you can still target the square.