>In Pokémon X and Y, Mulch can be acquired from one of the Berry fields composters. By putting in different combinations of Berries, different kinds of Mulch can be produced. If traded to Pokémon Omega Ruby and Alpha Sapphire, Mulch cannot be used, as the soil is unsuitable for Mulch.
Yes, you can get it in ORAS, but it cannot be used. The only way to get it is by trade.
Source: Experience and above link