Notice that 飾る has a different nuance between 花を飾る and 玄関を飾る. The former is closer to "to put", whereas the latter is "to decorate". Therefore 花で玄関を飾る has a nuance of "being filled with flowers", not only the ground but maybe also the walls or door. It's also same for 壁に絵を飾る vs. 絵で壁を飾る. The former is "to put a picture on a wall", but 絵 might not be singular in the latter.