Baking soda neutralizes the ph in the soil and nothing will grow there. Use baking soda in a 6" wide area around all of the edges of my flower beds to keep the grass and weeds from growing into my beds. Just sprinkle it onto the soil so that it covers it lightly. Do this twice a year - spring and fall.
Why Use Roundup? Make Your Own Weed Killer Note: spray on the plant, it will kill anything tender that it touches. If it gets in the soil, the salt in it will prevent anything from growing for a few months to several years, depending on how much was used.