Gather acorn tops that have fallen from the trees. Place acorn tops in a bowl of water to soak. Use a toothbrush and a little baking soda to clean them off if you wish. Rinse, drain and pat dry with a towel.
Place the acorn tops on a cookie sheet and bake in a preheated 225 F oven for about 40 minutes. This will kill any remaining insects that may be hiding and will also dry the acorn tops. Remove from oven and let cool on a paper plate in a single layer.
Apply a generous amount of glue to one section of the frame at a time. Cover with acorn tops, hanging the ends of the acorns over the edges of the frame if needed to fit.
Once the frame is completely covered, fill in all the gaps between the acorns with craft glue. Let dry overnight.