Crossword Genius

Flower holder for mushroom? (6)

Ross

I believe the answer is:

deepen

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But I can't explain it at all! Could you help me understand?

(Other definitions for deepen that I've seen before include "Make (colour) darker" , "Get stronger" , "Dig out" , "Make stronger" , "make room for more water" .)

I've seen this clue in The Hindu.
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