Eco-friendlier Weed Killer

img_20180618_103235087Even though we have a laissez faire–approach to vegetation and lawn growth, some places can’t have weeds. One of them is our garden beds, but we take care of that through sheet mulching (to be covered in an upcoming post). Another is pathways, and in this case, we can use an environmentally friendlier plant killer than RoundUp or other harsh chemicals. In fact, you’ve probably consumed these ingredients recently. A big thank-you to my friend Tony in St. Louis for turning me on to this.

Salt and Vinegar

The main ingredients are salt and vinegar, which you probably have in your kitchen right now. Together, these chemicals break down the cell walls and cause the plant in contact with them to die. Indeed in the ancient world, victors would sometimes sow salt into the fields of the defeated foe in order to make them less fertile. In a recent book (Why did Ancient Civilizations Fail?), I wrote about salinization through irrigation in ancient Mesopotamia:

The fundamental flaw in Mesopotamian agriculture, though, was not dependence on precipitation, but its method of irrigation. Without humans modifying the landscape, the Tigris and Euphrates would build up their floodplains with silt deposited each spring. When the silt grew too high, the rivers would bust their banks and form new primary channels. The salts dissolved in the rivers from the distant mountain sources were washed out to sea. When canals and levies were built, however, this self-regulating system was disrupted. The Tigris and Euphrates are relatively salty to begin with, and as the water was slowed in canals, more of it evaporated, increasing its salinity. Because the river was kept in the same course, the silts grew higher than would occur naturally, further reducing the flow of water in the rivers, canals, and fields. The alluvial flood plain has poorly drained soils, which tend to concentrate salt in the upper layers, instead of flushing it down into the water table. Compounding this problem is the high watertable, which is (you guessed it) also relatively saline. Salt occurs naturally in low-lying, poorly drained, arid soils, which is exactly how Mesopotamian farmers designed their fields.

Farmers were aware of salinization and attempted to mitigate its effects through various strategies: increasing drainage of fields, flooding fields right before planting to leach away surface salts, using weeds on fallow fields to absorb excess salinity, and abandoning overly saline fields for a lifetime to let natural processes restore equilibrium. Mesopotamians chose crops that were best suited to the saline level of the soil: wheat is more sensitive to soil salinity and it was planted in the least-saline fields. Over time we see saline-tolerant barley replacing wheat in the archaeological record, indicating an increase in soil salinity over time. . . It is ironic that Mesopotamians, by attempting to enlarge their arable land through irrigation, actually reduced the amount of farmland because of the salinization caused by over irrigation.

The main consideration to take into account is that this may cause any location where it is applied to be vegetation free for months or years, depending on the strength of the application.

Weed Killer Recipe

  • 1/2–1 gal white vinegar (5%)
  • 1 C salt (any type)
  • 2 T dish soap (optional)
  • up to 1/2 gal water

Pour the vinegar into a pot and add enough water to bring it up to a gallon. Heat on high and add the salt, stirring until it is dissolved. For extra contact-killing power, boil the mixture and apply while still hot, or, for easier handling, let the liquid cool and then apply with a pressure sprayer or watering can. A little dish soap will help the mixture cling to the plants have have more efficacy.

Some complain that this is more expensive than RoundUp and that it is not a systemic killer (that is, it only kills what it contacts; it is not taken up by the plant circulatory system and brought into the roots). What this critique doesn’t take into account is the aversion many — including the EU, which only narrowly approved its application — have against the active ingredient glyphosate. Furthermore, the author states that “pound for pound” salt and acetic acid (vinegar’s main ingredient) is more toxic to mammals, which is true, but comparing a pound of acetic acid to a pound of glyphosate is a little disingenuous, since they are applied in a diluted state.

You can find more resources on this in other places on the internet: Weed Control Freaks and San Francisco Gate are good ones. The latter suggests using rock salt on pathways and we’ll be doing this as we build a paver patio: sprinkling salt below the bricks to help keep away weeds instead of using a large plastic barrier.

Kill Stumps with Salt

StumpI had to take down a few trees that were growing into the siding of our house. After cutting it down, it resprouted with suckers. Then I remembered how to kill a stump with salt: drill holes into the stump and fill with salt. For every 4 in diameter, I drill one 1/2-in-wide, 3-in-deep hole and fill it with salt. Then I put something on top to keep the rain off, like a brick. The holes need to be refilled occasionally, but this will dessicate and kill any new growth.


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