[titan7]

Can I just put the wires in a trench that will be under the concrete slab or do they need to be in PVC conduit?

 

[Arrow3030]

You're required to have a chase under a slab. A slab walkway that breaks up landscaping for instance should have a pipe going under it.

 

[titan7]

It a patio slab that it needs to go undera slab

 

[MrElectricianTV]

Can I just put the wires in a trench that will be under the concrete slab or do they need to be in PVC conduit?

If the wires are rated for direct burial, than you can put them in a trench. I agree that putting a conduit under the slab is a good idea for future use and to protect the wires.

If the wires are only rated for wet locations, they will need to be in conduit all the way.

If the wires do not have any outdoor, wet, or sunlight resistant ratings, they should not be used outdoors or in the ground.

 

[Oso954]

Definitely put the conduit in.

Both LV landscape wires and sprinkler wires are subject to damage. Once they have been damaged and spliced, they are subject to water intrusion and corrosion if the repair splices are not perfect. Over time, you may not have any recourse other than replacing the wires under the patio.

Do you want to tear up the patio at that point ?

The only other good solution is to look for another location for the LV transformer and sprinkler control. You could relocate them now and avoid wires under the patio.