These fall centerpieces begin with greening in the pumpkin. Common and inexpensive foliage that is a standard in every flower shop is leather leaf fern.
It has glossy green leaves with separated fronds that work beautifully in all flower designs.
Work with the natural curve of the leaves, allowing them to arch gracefully down the sides of the pumpkin arrangement.
Note how the green is inserted in the side of the design, coming out and then curving downward. If you had cut the foam too short (level with the top), the greenery would be sticking straight upward. This is a common mistake of an amateur.
I like to cut my greens, giving a sharp clean edge to the fern stems and allowing a clean insertion. Don't discard the leaves you strip off the bottom, but insert them into the foam as well.