Check out this Artist:
He does some amazing natural artworks using things we can find out side.
Here are some other Ideas for making Art Outside.
Build Rock Cairns by stacking and balancing different sized rocks on top of each other. Mr. Blake has posted some of hi creations on Class Dojo, maybe you saw those. Big rocks are easier to stack than small ones, but they are heavy so be carfeul.
Use something wet, like a stick or rag to create temporary water paintings on concrete or another dry surface.
Weave me Alone
Sit down and take a quiet moment to create a weaving using sticks, leaves, or other fibrous natural material. Remember you need to make a loom with warp before your weft does the over-uder-over-under pattern.
Will it float?
Make a boat out of found objects. Will things other than wood float? What about paper? Plastic? That piece of candy wrapper or an empty soda can?
Painting with Rocks
Organize rocks by color then create a pattern or design
As with all activities, get your parent or guardian permission and if possible supervision.