Commercial weed killers purchased at gardening centers and hardware stores often contain chemicals that do not jibe with organic gardening practices. If you're concerned about these chemicals, you can easily make an amazing homemade weed killer that will not damage plants with man-made chemicals. This inexpensive homemade weed killer recipe, recommended by the author of "Month-By-Month Gardening," works well on weeds both in the garden and in driveway and sidewalk cracks.
Wash and dry the spray bottle. Pour 1-1/2 cups of 10 percent acetic acid vinegar into the bottle, using a funnel if necessary. This type of vinegar, which is quite a bit more acidic than vinegar used in cooking, is generally available at hardware stores and gardening centers.
Add 1/2 cup of mild dishwashing soap to the vinegar, swirling gently to combine. The soap will help the vinegar stick to the weeds long enough to kill them.
Spritz the solution on the weeds, focusing on the foliage and the base of the plants. Be careful to avoid any plants that you don't want to kill.
Make a shield from a gallon-sized milk jug to use if you're spraying weeds in a particularly tight area (such as a garden). Slice the bottom off of the jug with a knife, then place the jug over an individual weed or clump of weeds. Spray the solution onto the weed through the small opening in the top of the jug.
Repeat this process as new weeds develop. The spray will have a residual presence in the soil and can keep weeds from coming back as well if it's used on a semi-regular basis.