Decorate cake. Using spatula and light green icing, roughly ice cake, leaving spatula marks on sides and top of cake.
Using medium green icing with pull-out star technique, pipe cacti in various heights and sizes. Using light magenta icing, pipe star on top of each cacti. Using white icing, pipe pull-out dots to form needles on cacti ridges.
Using striped bag with pull-out dot technique, pipe leafy succulents, starting at outside and working towards center.