Your dog experiences his world primarily through his nose. Scent leads him to some objects -- including sticks, leaves and dirt -- that he wants to investigate further with his mouth. Puppies under 6 months old are especially notorious for eating everything in sight, whether edible or not. While sticks, leaves and dirt are natural items favored by many dogs, letting your dog eat them is sometimes a dangerous proposition.
Stick to It
A dog with retrieving instincts will readily chase a thrown stick, but just about any dog will settle down to chew on one. Sticks that have fallen off the tree and had time to dry pose a risk of splintering, causing injury to your dog's mouth, throat or intestinal tract. Freshly fallen sticks don't pose as great of choking hazard but may have toxic substances that make your dog ill. The ASPCA website lists 65 types of common trees poisonous to dogs on its toxic plants list, including apple and other fruit trees as well as popular landscaping trees.
Do It in the Dirt
Dogs enjoy supplementing their diets with a bit of dirt or greens -- such as grass and leaves -- that provide living enzymes and nutrients they lack in their commercial food. In the wild, wolves eat the stomach contents of herbivorous prey first to get enzymes from the leafy matter, and they spend days when meat is not available nibbling on leaves and berries. As long as leaves are nontoxic to dogs and you don't apply chemical fertilizers or pesticides to your soil, its okay if your dog nibbles a few leaves or ingests a mouthful of dirt here and there. Adding pet-safe fresh vegetables to your dog's diet sometimes reduces leaf and dirt eating behavior. Dogs are known to much on leafy material, including grass, when they have stomachaches.
Stop the Madness
A puppy normally grows out of putting everything he can in his mouth by 6 months to 12 months old. If your dog is regularly obsessed with eating sticks, dirt and leaves, and he's getting plenty of nutrition, he may have a disorder known as pica. Make sure your dog gets plenty of one-on-one time with you, and has toys and chews that provide a better alternative to items found around your yard, as boredom is often a factor in pica. Puzzle toys with treats hidden inside help keep his nose, brain and mouth fully engaged for extended periods of time. Consult your veterinarian if eating sticks, leaves and dirt persists.
The Great Unknown
Teaching your dog the commands "leave it" and "drop it" helps keep your pet out of danger in unfamiliar surroundings such as on a walk or hike where unfamiliar plants, trees and soil may pique his interest. To clarify the command, it helps to have a tasty bite-size treat reward to exchange for the item you command him to leave or drop. Should you see your dog eating leaves or sticks from a plant you are unfamiliar with, take a sample with you for identification by your veterinarian should your dog begin showing symptoms of toxic poisoning.