According to the University of Kentucky, boric acid works so well because it is not an insect repellent. Cockroaches will return to the treated area again and again, carrying the boric acid back to their nest. The most common method is to sprinkle the powder along baseboards and in floor cracks. Commercial spray solutions are available, but it is easy and cost-efficient to make your own.
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Mix 3/4 of a cup of boric acid, which is available at any home improvement store, with 1 gallon of water. Mix thoroughly. Pour the solution into a plastic spray bottle.
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Remove all serving dishes, pet food, water dishes and any food from counters and floors where you intend to spray.
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Spray a generous amount of the boric acid solution along baseboards and the back of counters, avoiding any food-preparation surfaces. Let the solution dry.
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Re-apply every other day for two weeks, or until you no longer see any cockroaches.