The keywords, FIRST, SECOND, THIRD, and  FOURTH differ only by their first letters.

Come FIRST to my garden. Put plants in 

   the pot.

They SECOND will flourish, or THIRD on

   the spot.

Don't be in a FOURTH. Just stay calm.

   Tend the plot. 

Answers:

 

HITHER

EITHER

WITHER

DITHER

 

Credit:
The Enigma

April, 2023

BROBBERTY