Greetings from the Pacific Northwest.

I am building a makeshift bamboo planter for p nuda bamboo. The intention is
to fit two recycled Yoshida barrels, sawed in half lengthwise, into a
trench.

My question regards the drainage holes. I believe I should have some holes
drilled in there. Ideally, they would be the right size for water and root
fibers, but too small for the rhizomes to penetrate and start growing in my
neighbor's yards.

Is there an ideal size? And how many holes would a half 55 gallon barrell
need

Thanks

Nathan