If you planted Mexican Weeping Bamboo(Otatea acuminata ssp. aztecorum), or one of it's varieties, which all look very similar to Elegia capensis, then you probably wouldn't need a barrier. Do some research and decide for yourself.

The barrier depth depends on how deep the roots grow on a particular plant. Tap roots aren't anything to worry about, it's the roots that grow parallel to the ground that are troublesome. They are the ones that will produce new plants. Most barriers are available for a depth of about 36 inches.

Kt