The ornamental design for a holder for flower or plant pots, as shown and described.
1.1 : Perspective
1.2 : Front
1.3: Back
1.4: Top
1.5: Bottom
1.6 : Left
1.7: Right
The portion of the design shown in the color gray is for the purpose of illustrating portions of the holder for flower or plant pots that form no part of claimed design.