Is it liturgically correct to have boulders and dried-up plants in sanctuary by the altar during Lent?

Regarding the decoration of the altar area during Lent, the General Instruction of the Roman Missal states:

Moderation should be observed in the decoration of the altar . . . During Lent it is forbidden for the altar to be decorated with flowers. Laetare Sunday (Fourth Sunday of Lent), solemnities, and feasts are exceptions. Floral decorations should always be done with moderation and placed around the altar rather than on its mensa. (GIRM 305)