Crossword Genius

Spring greens go mushy without nitrogen, Yankee admitted (6)

Ross

I believe the answer is:

geyser

I'm a little stuck... Click here to teach me more about this clue!

'spring' is the definition.
(a geyser is a naturally forming hot spring)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for geyser that I've seen before include "Spring spouting steam and hot water" , "A jet of hot water from natural spring" , "Natural spout of hot water" , "Spring that discharges steam and hot water" , "It blows off steam" .)

I've seen this clue in The Independent.
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