Items you will need
Fleas multiply quickly. It doesn't take long for them to spread from your pet, to your home and even to your garage. The sooner you begin to get rid of the fleas, the easier it will be. You must treat your pet for the fleas before you begin treating your garage. Otherwise, your pet will visit the garage and infest it with fleas all over again. Getting rid of the fleas in your garage is not hard, and you can even enlist the help of your older children.
Remove all of the items on your garage floor. This may take awhile if you have a lot of tools or stored items, but it is necessary.
Vacuum the garage floor, and throw the vacuum bag away in an outdoor trash can. Make sure you seal the vacuum bag in a trash bag first. This will get rid of a good number of the fleas.
Sprinkle borax all over the garage floor. Borax can be purchased in the laundry aisle of your grocery store. One large box will cover a small garage, so if your garage is on the larger side, pick up two or three boxes.
Wait 24 hours for the borax to kill all of the fleas. The borax will pierce the exoskeleton of the flea and cause it to suffer from dehydration. Without the ability to retain water, the flea dies.
Vacuum up the borax and discard the vacuum cleaner bag.
Mix one gallon of hot water with five tablespoons of flea shampoo. Use this solution to wash the floor of your garage. This is a good backup method in case any of the fleas managed to avoid the borax.
Fleas hate the smell of cedar. You may want to set some bowls of cedar chips around the garage to discourage the fleas from returning.
If your garage does not have electricity, you may need to run an extension cord to use the vacuum.
Keep your pets away from the garage until you have finished using the flea shampoo.