Whether your home is built on a slab, raised perimeter or other type of foundation, it comes in contact with bare earth. However, contact with the ground is not a good thing, it is the pathway to destruction via moisture and insects. To preserve your home's exterior siding and foundation, you must ensure that dirt, dense vegetation, mulch or anything the can hold moisture against your home is properly cleared away.
Periodically and especially before the wet season, you should inspect the perimeter of your home. The concrete portion of your foundation has to be in contact with the ground, but all other materials must be have adequate clearance. Wood siding, stucco, vinyl, brick - all siding, should ideally have at least 6 to 8 inches clearance above the ground. Any clearance is better than none. If the adjacent ground is concrete, such as part of a patio or a sidewalk, it still requires the same clearance as bare earth.
The reason for this clearance requirement is that while moisture will rot wood and damage other siding, even if the ground isn't holding water against the siding, rain splashes up and soaks the siding. Also, the closer to the ground the siding, the more easily termites can go undetected and the more easily rodents can bore their way into your home.
Remove dirt or other material to lower the grade until proper clearance is created. It isn't always possible to provide the required clearance. Don't try to create clearance by trenching next to the foundation. Creating a trough for rainwater to collect is probably worse than having inadequate clearance. What you can do is make sure the ground slopes away from the foundation so water will run off. Make sure all downspouts have splash blocks or even better, extenders to carry the water away from the foundation.
Cutting back plants from the walls is a good idea, especially dense foliage and ivy. Plants can hold moisture against the building, slow down the drying effect of circulating air and they provide a hiding place for rodents. Cutting plants back just a few inches is all that is needed.
While you are inspecting the perimeter, keep an eye out for mud tubes going from the ground up to the siding. These tubes are little termite highways. Termites build them to protect themselves from sunlight and predators. If you find the tubes, note there locations, destroy them and take appropriate steps to treat for termites and inspect for structural damage.
Inspection is easy and should take no more than 10 minutes. Remedying any problems you find will be easy in most cases. A small amount of effort will pay large dividends in protecting your most valuable asset. Don't let a simple problem cause serious damage to your home.