Re: landscape wiring in conduit
If its a listed system, it would be installed under the provisions of Art 411. Art 411 does not require conduit. If the system is not listed, then it could fall under the rules of Art 725, and it would depend on the power (VA) of the "low voltage" system. Once you exceed the power limits in Art 725 then you have to use a chapter 3 wiring method.
For the typical "malibu" system, conduit is not required.