When to plant after using weed killer?

Julia purchased her first home in time for spring and she was excited to plant a garden. She found the perfect spot, but the area was completely over-grown with grass and weeds. Julia was eager to clear the area and prepare the soil for her garden so she asked her local retailer for advice. The retailer recommended a pesticide that kills weeds. He told her to apply the product to the unwanted plants according to the label directions, and she should start to see results within a couple of days.

The next day Julia sprayed the weeds with the product. After a few days Julia was thrilled to see the weeds begin to wither and lose their green color. However, she began to wonder what this meant for desirable plants nearby, and the vegetables she would soon plant in the soil. Would the product move through the soil and harm her flowers? Would it stay in the soil and prevent her vegetables from growing, or cause them to wither like the weeds? How long should she wait to plant the garden? Julia had many questions and decided to call NPIC for answers.

Take Home Message

Julia learned that some herbicide products contain at least one active ingredient called glyphosate. Glyphosate is a post-emergent, nonselective herbicide that is absorbed through the leaves following application, and moves throughout the plant, including the roots. Glyphosate works by preventing the plant from making certain compounds necessary for survival.

Julia also learned that, once applied, glyphosate tends to stay put in the soil with limited movement to untreated plants, such as her nearby flowers. In the soil, glyphosate generally breaks down within days to weeks, and the way it sticks to the soil makes it less available to untreated plants that may grow in the same soil at a later time (such as Julia's vegetables).

The NPIC specialist explained that there are many different weed killing products available to consumers. Some are suitable to use for garden plot preparation and some are not. Consumers should always read the product label carefully to be sure their product has been approved for this use. Julia also learned that the product label would help her determine how quickly she could plant her veggies following application. Julia read from the product label that she could plant cucumbers and peppers now, but she would have to wait a few weeks before planting her tomatoes and herbs. The NPIC specialist also provided Julia with the telephone number for her local Cooperative Extension Service to obtain additional advice about preparing the soil before planting her garden.