This is a really cool fabric dyeing technique that I learned when I was younger.
It's surprisingly simple: all you need is a hammer, some fabric, a flat surface, and some plants.
Well, and something to fix the dye helps.
Step 1: Lay Out Boards
Step 2: Cover Boards
Paper towels are a good material for this. This will help protect your surface from plant colors.
Step 3: Place Fabric on Boards
Step 4: Lay Out Plants
Ferns and green things work best.
Step 5: Tape Down Plants
Step 6: Carefully Flip Over the Fabric
Step 7: Hammer!
Step 8: Iron
Step 9: Flip Right Side Up and Remove Plant Gunk
Step 10: Fix Dye
Soak it in a salt bath!
I'm not actually sure how effective this is.