The ornamental design for a growingsystem for plants, as shown and described.
FIG. 1 is a top and front perspective view of a growing system for plants showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a side elevational view thereof; and,
FIG. 5 is a rear elevational view thereof.
The broken lines disclosure is understood to represent a portion of the article in which the claimed design is embodied, but which forms no part of the claimed design.