With the trend towards environmentally friendly treatments for lawns increasing, the use of natural weed killers for lawns has re-emerged as a common method of weed control. These natural methods have many advantages such as speed and effectiveness; they also have disadvantages such as the short duration of effectiveness and potential damage, depending on the type of material used.
Natural weed killers are organic, simple substances that are found in nature and can eliminate weeds. These substances occur in small amounts in nature and are not harmful in these portions. In large amounts, these substances can cause adverse affects quickly. Examples of natural weed killers for lawns include salt, alcohol, boiling water, organic acids, bleach, vinegar and heat from steam.
Most natural weed killers alter the cell structure of the affected weed. Natural weed killers are good for individual plant removal and spot applications. You can apply them to both foliage and root systems with the same effectiveness.
There are three types of natural weed killers: acetic acids, fatty acids and water-based. The acetic acids change the chemistry of the roots and cell sap. Damage occurs rapidly and can increase in speed during higher temperatures. An example of this type is vinegar with a 15 to 20 percent acetic acid solution.
Fatty acids dissolve plant membranes and dehydrate the plants. The use of salt is one such method. Water-based applications include boiling hot water and steam. This method kills weeds using a rapid increase in heat, thereby burning the plant.
The lasting effect of many natural weed killers for lawns is not as long as for chemical treatments and may require multiple treatments to be effective. An example is the application of acetic acids that have effective control within 24 hours of application, but require three treatments of high acetic acid solution to remain effective. Water-based treatments may last only 24 hours, and the weeds may recover. On the opposite end of the spectrum is salt, having a near permanent effect on treated areas when used in high amounts or over long periods of time.
Natural weed killers are not selective and will kill or severely damage any plants they come into contact with. Dead spots can appear in areas where you use natural weed killers. Excessive use of salt can poison soil, causing permanent damage to bacteria, earthworms and beneficial micro-organisms. Salt is not biodegradable, making runoff from affected areas a problem: excess salinity can spread to surrounding areas.