Wash the outside of the pumpkin with soap and warm water to remove any dust and grit. Dry off the pumpkin.
Draw a circle around the top of the pumpkin to mark where you’ll cut the opening for the vase or the foam.
Using a sharp knife, carefully cut off the top of the pumpkin. Make sure the opening is wide enough for your vase or foam to fit through. Scoop out all the pumpkin seeds and pulp.
Mix one tablespoon of bleach with 4 cups of water. Add the solution to a spray bottle, and use it to spray the inside of the pumpkin to help kill mold and bacteria. Rub the cut edges of the pumpkin with petroleum jelly to seal.
If using a flower vase: Chose a vase that will fit inside the pumpkin, and not be visible outside the pumpkin. A small flower vase or mason jar are just two examples. If using floral foam: Trim the floral foam to a size that will fit inside the pumpkin.
If you’re using wet floral foam (for fresh flowers), soak it in water first so that it’s nice and hydrated, before placing it in the pumpkin. Cut it to fit snugly inside the pumpkin. If you’re using a vase or jar, fill it with water and place it inside the pumpkin.
Trim the Flowers. Cut the flower and greenery stems to varying lengths for a more natural, layered look. On fresh flowers and greenery, remove any leaves that would sit below the waterline—this helps to prevent them from rotting.
Next, arrange the flower stems. Start by arranging the bigger flowers—like sunflowers or dahlias, placing them evenly around the pumpkin. Fill in the gaps with smaller blooms like mums or roses.
Add your greenery or accents like eucalyptus, wheat stalks, berry stems, or fall leaves, around the edges of the flower arrangement for a full, lush effect.
Place your pumpkin arrangement as a centerpiece on your dining table, entryway, or anywhere that could use a fall centerpiece for decoration.