Create a border around around the intended mulch or rock bed area. Borders may be very short wooden fences or strips of thick rubber. Gardening border is available at most commercial outlets.
Place mulch around plants. Surround the plants with the mulch covering the root radius of the plants. For some this may be a small area, while others, such as small trees, may have a wide root radius.
Lay garden sheeting or strips of plastic in the areas intended for the rocks. This will prevent weeds and grasses from growing in the rock area. Cut the plastic to fit the area. Clear away debris from the area and smooth the dirt prior to laying. Slope the plastic in the desired direction for water run-off. For plants in need of more water, slope the plastic toward the plants. For wetter areas, slope the plastic away from the roots.
Spread the rocks onto the plastic area, around the mulch. Smaller rocks may mix with mulch at the edges. Larger rocks may give a neater appearance, as they will allow for less mixing with the neighboring fibers.