Time Frame

• Strong-smelling natural plant products like garlic, as well as basil, citronella and eucalyptus, are effective mosquito repellents for up to two hours, according to the Mississippi State Department of Health.
  
  

Amount

• Commercial garlic sprays will have instructions on how much to use in a backyard. Homemade garlic sprays should have a ratio of one part crushed garlic to 64 parts water. A one-gallon spray bottle is sufficient, because the garlic spray is used on tablecloths, chairs, plants and other areas mosquitoes may congregate as opposed to the entire backyard. Another method of employing garlic is to eat a clove of raw garlic or take garlic supplements.
  
  

Considerations

• Chemical mosquito repellents like DEET can be dangerous to use on children or animals, and natural methods like raw garlic spray are harmless. Similarly, it can be dangerous to the ecosystem to spray insecticides outdoors, making garlic spray a healthier option. However, garlic is potentially toxic to cats, so avoid using garlic spray in areas where cats congregate.