The ornamental design for a vertical plantpotholder, as shown and described.
FIG. 1 is a front elevation view of a vertical plant pot holder in a position of use with portions of the article not claimed;
FIG. 2 is an enlarged detail view of the area circumscribed in FIG. 1;
FIG. 3 is a perspective view of FIG. 2;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The evenly-spaced broken lines shown in the drawings depict portions of the vertical plant pot holder that form no part of the claimed design. The dot-dash-dot broken lines denote the boundary of the claim and form no part thereof.