Line a greased 15x10 inch jelly roll pan with parchment paper; grease paper too.
In a large bowl, combine the first 5 ingredients until well blended.
Combine remaining dry ingredients and add gradually to the pumpkin mixture. Pour batter into the prepared pan.
Bake at 350^ for 20-25 minutes or until a toothpick inserted near the center comes out clean. Cool for 5 minutes before inverting onto a wire rack to cool completely. Carefully remove the paper.
In a large heavy saucepan over low heat, combine the syrup, egg whites and cream of tartar. With a portable mixer, beat on low speed until frosting forms stiff peaks, about 7 minutes. Remove 1/4 cup mixture divide up into 2 small bowls and tint 1 with green and 1 with yellow food coloring and set aside.
2Cut cake width-wise into thirds. Place one layer on a cake platter. Spread 1/3 of the remaining frosting between the layers and on top - do not frost the sides- just let the frosting ooze out if it wants too.
Arrange candy pumpkins on cake , add vines with reserved frosting and little yellow pumpkin blossoms.