The ornamental design for a sphagnumcolumn, as shown and described.
FIG. 1 is a perspective view of a sphagnum column showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is a perspective view of the sphagnum column where the sphagnum column is in an open state; and,
FIG. 10 is an enlarged view of portion 10 shown in FIG. 2.
The dash-dash broken lines in the drawings depict portions of the sphagnum column that form no part of the claimed design. The dot-dash broken lines represent boundaries of the enlarged portion and form no part of the claimed design.