Hand weeding is time consuming and---many gardeners believe---hard work. Chemical sprays and granules kill weeds effectively, but are often not considered safe for humans and animals. No wonder, then, gardeners often seek a safer weed killer. Back when borax was popular for washing, gardeners noticed washwater poured in the garden sometimes killed weeds.
Some gardeners mistakenly believe borax is a proven, all-purpose weed killer. However, Iowa State University, which conducted the initial testing on borax as a weed killer, found it effective only on ground ivy ("Glechoma hederacea," or "creeping Charlie") growing in turfgrass. The Iowa State University website states, "Borax should not be applied to flower and vegetable gardens ... [where it] may damage or destroy many of the flowers and vegetables."
The benefit of using borax as a weed killer is that it is less toxic than manmade chemicals. Borax is a naturally mined mineral and, if used properly, is safe for use around humans and animals. Borax is also considerably less expensive than chemicals found in gardening centres.
Borax contains boron---an element all plants need to thrive. However, plants only need small amounts of this element; larger doses are toxic. Just how sensitive plants are to boron varies greatly. The reason borax works to kill ivy in turfgrass is that ivy is more sensitive to boron in soil than in grass.
Iowa State University suggests using Twenty Mule Team brand borax. Dissolve 5 teaspoons in 1 quart of water and pour it in a garden sprayer. Spray uniformly over 25 feet. For larger areas, dissolve 284gr of borax in 2 to 3 gallons of water and apply evenly over 1,000 square feet. The University of Iowa's website stresses that application must be even and applied to the correct area, or the grass may die, too.
Borax is toxic if ingested by people or animals. If handled with bare hands, it may cause redness or a rash, so handle borax only after donning rubber gloves, and store it out of reach of children and pets. According to Dirt Works, a provider of "Earth friendly" gardening products, apply a borax spray only in the spring and for no more than two years. Otherwise, the soil may contain too much boron and kill the grass.