Plant everyone observes at end of field (7)

I believe the answer is:

allseed

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'plant' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?

'everyone observes at end of field' is the wordplay.
'everyone' becomes 'all' (all people).
'observes at' becomes 'see' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'end of' suggests the final letters.
The final letter of 'field' is 'd'.
'all'+'see'+'d'='ALLSEED'

Can you help me to learn more?

(Another definition for allseed that I've seen is " Unwanted growth".)

I've seen this clue in The Times.

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