What should be done with the exposed ground under the deck?

Very little will grow under a deck and relatively few decks have anything underneath them besides dirt.

If anything, pitching the grade the correct way for water runoff and making sure leader pipes are secured and draining properly is more important.

If you like more of an assurance that nothing will grow or would like to dress up the underneath of a deck, landscaping fabric can be installed with a layer 2-3 inch layer of 3/4 inch crush stone on top.

For elevated decks that are high enough, concrete patios or pavers are sometimes installed.