How Long to Wait Before Transplanting Vegetables to a Garden Area Where Herbicide Was Applied

Glyphosate Products

• Glyphosate is the active ingredient in several common ready-to-use and concentrated weed killers. While glyphosate is a non-selective herbicide, it is only effective on actively growing green plants. The herbicide is absorbed through the leaves and circulated throughout the plant, killing the weed down to the roots. The label states that vegetables may be planted three days after applying the weed killer. Because glyphosate may take up to four weeks to kill the weeds, applying the herbicide a month ahead allows you to kill the weeds and remove them from the garden bed before setting out your transplants

The Persistence of 2,4-D

• Another herbicide found in many weed killers that are readily available to the public is 2,4-D. Like glyphosate, 2,4-D is a non-selective herbicide. Its half-life in the soil is seven days, meaning that its toxicity to plants decreases by one-half in seven days, to one-quarter in 14 days and one-sixteenth in 28 days. In general, you can transplant vegetable seedlings one month after applying 2,4-D to weeds. Always check the herbicide's label for specific instructions regarding planting times; the manufacturer might have another herbicide mixed with the 2,4-D, which can change the rate of degradation.

Selective Herbicides

• Some herbicides are selective, only affecting specific families of plants. Herbicides such as bentazon, dimethenamid and siduron are generally effective for one to three months in the garden. Depending on the specific herbicide and the weeds targeted by its formulation, you might be able to plant vegetables in a few days or after three months. The label on the herbicide container should carry specific information on what plants are affected by that particular herbicide.

Residual Herbicides

• Residual herbicides are used on the soil in areas where you don't want any vegetation, such as gravel walks, driveways and next to outbuildings. However, once you've decided to plant a garden, that might be the only place with sufficient sunlight for vegetables. Herbicides such as clomazone, diuron, oryzalin and trifluralin generally persist for three to 12 months in the soil. Transplanting vegetables into an area sprayed with any residual herbicide is risky. Consider using containers for the first year before turning the soil and using the garden bed for vegetables.