Step 1: Tumbleweed Shopping
Step 2: Score!
I gathered a few different kinds to have the best selection. Most tumbleweeds have leafy remnants and spiky protrubances that could require more cleanup work, so I suggest finding the smoothest one possible with the least bugs living in it.
Step 3: Cleanup
Next I snap off any unruly branches that jeopardize the overall shape. The bottom has an extra long stem so I took a little hand saw and cut it down.