Which Liquid Kills a Plant Faster, Saltwater or Vinegar?

Salad Dressing or Weed Killer?

• In 2002, the USDA Agricultural Research Service performed an experiment in which vinegar was used to kill weeds. The acetic acid in vinegar kills the leaves -- preventing food from being made -- and lowers the pH of soil. The researchers found that vinegar with a 5 percent or 10 percent concentration of acetic acid killed most weeds within two weeks, but this was on weeds that were only two weeks old. Vinegar is most effective on newly sprouted weeds. Older weeds required vinegar with higher levels of acetic acid. Household vinegars usually have a 5 percent concentration. Vinegar with a 20 percent concentration was found to kill some established weeds in as little as two hours. So, the amount of time it takes to kill a weed with vinegar depends in large part on the age of the weed and the concentration of acetic acid in the vinegar.

Season Your Weeds

• Salt -- even ordinary table salt -- contains sodium and chloride, both of which are toxic to plants. Salt dehydrates plants and interferes with food production. In fact, salting the soil can destroy crops for years to come, and the method was used in ancient warfare to ensure that the enemy would not be able to grow anything in the land it overtook. Some plants can resist salt more than others, however, and even salt-sensitive plants can resist salt for a while. It takes ongoing, concentrated applications of salt to kill a plant. In general, the higher the concentration of salt, the more quickly it will kill the plant. So, the amount of time it takes salt to kill a plant varies widely according to what type of plant it is, how large the plant is, where it is located and how concentrated the saltwater is. Salt tolerance varies so much, in fact, that there are conflicting reports about it, and data taken from plants at one location may not apply to the same plant in a different location, according to Purdue University Extension.

Recipe for Success

• It is hard to say which kills plants faster -- saltwater or vinegar -- because there are so many variables. You can, however, do some things to increase the potency of the vinegar by using vinegar that has a 10 percent or higher concentration of acetic acid. You can also increase the potency of your saltwater simply by heating it up. The Reader's Digest recommends combining salt with boiling water, which scorches the plant. Use a ratio of 1 cup of salt for every 2 cups of water. Plants that are exposed to plain boiling water usually take a few days to die, according to the University of Washington, but it's possible the salted boiling water will kill the plant more quickly. As for vinegar, combine 1 quart of white or cider vinegar with 4 ounces of concentrated lemon juice to make it even more acidic.

Tips & Tricks

• Apply the saltwater or vinegar to the plants on a dry, hot day, with the sun at its highest. If the plants are wet, the water may protect it from the solution. Put the vinegar solution in a spray bottle and be sure to protect your skin and other, nearby plants. Cover as much of the plant's leaf area as possible with the solution. With the boiling saltwater, simply pour it -- very carefully -- over the weeds, taking care not to splash it on yourself or on other, nearby plants.