Puppies like to have their noses in everything, and this definitely includes your houseplants. Whether your puppy is actually eating the dirt out of the planter or is just jamming his nose into the dirt to inhale the tantalizing aromas, it is a messy and annoying habit. The best way to stop your puppy from eating dirt out of your houseplants is through a combination of rearranging your plants and behavior modification.
Move as many houseplants as possible up off of the floor. Some planters may be too large to move, but if possible, keep the planters out of your puppy's reach.
Place pinecones or rocks on the top of the soil in the planters within your puppy's reach. Cover the soil entirely, pushing the items down into the soil slightly, so your puppy doesn't knock them out when he noses around.
Spray the pinecones or rocks with a taste deterrent. Be generous with the spray so your puppy will quickly learn to leave the planters alone.
Watch your puppy. If he gets near the planter, say "no" firmly and redirect his activity. He is probably bored and looking for entertainment.