The ornamental design for a platform for plants, as shown and described.
FIG. 1 is a front perspective view of the platform for plants;
FIG. 2 is a rear perspective view of the platform for plants of FIG. 1;
FIG. 3 is a front view of the platform for plants of FIG. 1;
FIG. 4 is a side view of the platform for plants of FIG. 1;
FIG. 5 is a top view of the platform for plants of FIG. 1; and,
FIG. 6 is a bottom view of the platform for plants of FIG. 1.
The broken line showings of the platform for plants are included for the purpose of illustrating portions of the platform for plants and form no part of the claimed design.