How to Use Borax for Killing Fleas on Hardwood Floors

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Not every pest control expert agrees, but an overwhelmingly large percentage recommend using borax for fleas. Enough have reported success to warrant attacking your own flea problem with the disinfecting chemical. Before you do so, you need to know two things:

  • Borax is mildly toxic and is corrosive to the eyes. There are safer alternatives.
  • Borax works best for flea control when used in conjunction with other chemicals.
How to Use Borax for Killing Fleas on Hardwood Floors
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Borax kills fleas by dehydrating their bodies, which requires that fleas come in direct contact with it. If the biting pests are living in the cracks in hardwood floors, you'll have to get the borax into those cracks to have any success. Once the job is done, it is important to clean up the borax to protect pets or toddlers.

Borax Isn't Boric Acid

Borax is a natural mineral mined from the earth. The world's largest mines are in the southwestern United States (where the famous 20-mule teams once operated) and in Tibet. Boric acid, on the other hand, occurs naturally in seawater, but most of it is derived from borax by reacting the mineral with hydrochloric acid.

Of the two, only boric acid is listed as an insecticide. It kills insects that ingest it. That is immaterial when it comes to flea control, however, because baiting does not work on these blood-sucking insects. They don't have the anatomy required to eat bait laced with boric acid.

The Difference a Molecule Makes

Technically, borax is a sodium salt of boric acid. The chemical name for borax is tetraborate decahydrate, and its chemical formula is Na2B4O7 • 10H2O. The chemical formula for boric acid, on the other hand, is H3BO3. The chemical formulae reveal two key differences:

  1. Both compounds contain born, hydrogen and oxygen, but borax also contains sodium, and the hydrogen atoms are bound into water in the borax molecule. Both compounds are powders, but borax can dry out and leave a film that is difficult to remove.

  2. The borax molecule is larger. This makes it less suitable for baiting than boric acid but more suitable for killing by dehydration. The large molecule may make ingestion more difficult, but it provides more surface area with which insects can come into contact.

Borax is readily available in grocery stores. It is used as a laundry detergent additive, a disinfectant and a flame retardant. Because it is so easy to obtain, you may be lulled into thinking that it isn't harmful. Don't fall for this misconception.

Borax Is Mildly Toxic

Borax is less toxic than boric acid. However, because it's a sodium salt of boric acid, the United States Environmental Protection Agency applies the same cautions to the use of borax as an insecticide as it does to boric acid. It is important to keep the following points in mind:

  • Pregnant women should not risk exposure to any borate product, including borax.

  • Exposure to borax can cause severe respiratory problems for cats and could even kill them.

  • Borax should never be used around food.

  • Prolonged exposure to borax can cause skin irritation for adults. Ingestion of more than 5 mg is considered dangerous.

  • Borax can harm plants.

Fleas In Hardwood Floors

Fleas are microscopic insects that reach an average length of about 2 millimeters, which is less than one tenth of an inch. If you have an infestation in your hardwood floor, it's a safe bet that they are hiding in the gaps between boards. An older floor with wide gaps has plenty of room for an entire colony of the little jumpers, which some people refer to as wood fleas.

How did they get there? The most likely flea vector in any house is a dog or cat, but it isn't the only one. An old carpet is another likely breeding ground, as is an old piece of plush furniture such as a couch or chair. You might even be the culprit. You may have carried the fleas in from a neighbor's house on your shoes or clothing.

Once safely sheltered in your floorboards, the fleas live their entire life cycle from egg to adulthood. It's important to remember this because the borax treatment affects only the adults and not the eggs. To effectively control the infestation, you'll probably have to repeat the treatment several times.

Dust Borax on Hardwood Floors and Repeat

It goes without saying that removal of all carpets, rugs and other floor coverings is a necessary prerequisite to borax application. You should also remove furniture. Take any furniture that may be flea infested outdoors and treat it separately. Close off the room to children and pets while the treatment is in progress.

Wear eye protection and gloves. Open the windows to provide ventilation while you are working but close them when you are done to prevent a draft from driving any of the powder into heating vents and broadcasting it throughout the house.

A Step-by-Step Procedure

  1. Vacuum the room thoroughly using a crevice tool in the gaps and around the edges of the room. Pay special attention to the baseboards. Fleas like to congregate there. Empty the vacuum bag outside.

  2. Spread a thin film of borax powder over the entire floor. If the room is large, you may want to do this with a garden spreader.

  3. Sweep the powder into the gaps and cracks in the floor using a soft-bristle broom. Use slow, gentle strokes to avoid raising dust. Be sure to sweep powder under the baseboards.

  4. Leave the borax on the floor for a period lasting from six hours to two days

    – the longer, the better. Do not allow young children or pets in the room during this time.

  5. Vacuum the floor thoroughly using a crevice tool to remove powder from cracks in the floor and from under the baseboards. Empty the vacuum bag outdoors.

Repeat the treatment after a week. That's how long it takes for eggs that were freshly laid before the first treatment to hatch. If you have a heavy infestation, it is probably a good idea to repeat the treatment twice.

Improve the Treatment by Adding Salt or Baking Soda

Borax isn't the only household compound that kills fleas by drying them out. Common table salt also does this, and it makes an effective additive. You need finely ground table salt or sea salt. Designer Himalayan salt crystals won't work.

Mix the salt and borax in equal proportions. Because salt is heavier than borax, the combination will sink more deeply into hardwood cracks than the borax will by itself. Salt is corrosive and will damage the floor finish if you don't vacuum it promptly after a day or two. Never allow the floor to get wet when salt is present.

Baking soda also kills fleas by dehydrating them, so adding this multi-use household standby to the borax is a way of fortifying it. There's no reason you can't mix salt, baking soda and borax together in equal proportions to make a triple-whammy flea killer.

Alternatives to Borax for Controlling Fleas in Hardwood Floors

If you are going to combine borax with salt and baking soda, there's also no reason you can't simply eliminate the borax. Salt and baking soda are both desiccants that will probably do the job as well as borax. Remember that the fleas aren't ingesting the mixture, so there's no reason to rely on the toxicity of borax to their digestive systems.

Diatomaceous earth, or DE, is another good substitute for borax and is one that is recommended by a number of pest control experts. It appears as a white powder, but it is actually composed of microscopic shells that kill insects by lacerating their bodies. Unlike borax, DE is safe to use around children and pets, and unlike salt, it won't harm the floor.

An Ounce of Prevention

A flea infestation can be difficult to eradicate, so it pays to prevent the little blood suckers from entering your home in the first place. They most commonly find their way inside on the coats of dogs and cats, so keeping your pets free of fleas is the best place to start your prevention program. Do not use borax for this.

You can use any type of flea shampoo for your pet, but if you don't have any, regular dish soap works. A weekly bath is always a good idea if you're worried about fleas. A bath is an absolute necessity when you notice your pet scratching or biting himself.

Consider Natural Repellants

Exterminators recommend a number of natural remedies for flea control inside the house. One is horse apples, also known as Osage oranges. If you live in the southern United States where these are common, you can cut them up and spread them around the house to repel all kinds of pests, including fleas.

Rosemary is another effective natural repellant. Dry out some rosemary leaves, grind them into a powder and spread the powder on the floor. It won't kill any fleas that are already living in the cracks, but it will keep away fleas that haven't yet arrived.

Don't Forget the Carpet

Your efforts to control fleas hiding in the floorboards will be for naught if you don't keep them out of the carpets and furniture as well. Borax is one remedy for fleas in furniture, although not necessarily the best one. Pest control experts do recommend borax for getting rid of fleas in carpets, though. Because of possible health issues, it is best to take the carpets outside for treatment.

Wait for a dry day, and then lay the carpet flat on the ground and dust it liberally with borax. Let the dust remain in the carpet for at least six hours, and then vacuum it thoroughly. Repeat the treatment after a week.

Don't Forget the Furniture

You can treat flea-infested furniture by washing it with detergent and water after vacuuming it. A single treatment won't kill eggs, though, so a repeat treatment will probably be necessary. As an alternative, use a commercial insecticide spray that includes an insect development inhibitor. It stops the eggs and larvae from developing into adults.

Another recommended method to kills fleas living in furniture is to dust the furniture with DE. Be sure to vacuum thoroughly after dusting with this compound.

If you decide to treat flea-infested furniture with borax, it's important to keep the furniture dry for the entire time of the treatment. Because the treatment involves two dustings spaced five to seven days apart, you'll need to find a safe place to keep the furniture for about a week. Vacuum thoroughly after each dusting has dwelled in the fabric for at least six hours.


Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at

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