If you want to control the flea population on your pet without using strong chemicals to kill and repel them, garlic isn't the solution. The notion that garlic is effective for controlling fleas is nothing more than an old wives' tale -- in fact, attempting to use it as a repellent can be unsafe for your pet.
Garlic is not just ineffective as a method of flea control, it is unsafe. According to the ASPCA, garlic -- and every other member of the onion family of plants -- is toxic to dogs, cats and some other household pets. Its ingestion can result in health problems like anemia, vomiting and bloody urine. A bite of food with garlic as a limited flavoring ingredient might not present symptoms; but a bite of garlic bread or food heavily flavored with garlic could be trouble. If you have given your pet garlic, consult your veterinarian as soon as possible. Ask your vet about safe methods of natural flea control to complement frequent washing of your pet's bedding and grooming with a flea comb.