The ornamental design for an planter, as shown and described.
FIG. 1 is a perspective front view of a planter showing my new design;
FIG. 2 is a front elevation view of FIG. 1, the rear elevation view being a mirror image thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is another front elevation view thereof.
The broken lines showing the stand, bucket, chains and inside surface in FIGS. 1-7 are included for the purpose of showing features that form no part of the claimed design.