Planting Grass After Roundup


Roundup is a brand of Monsanto Corp. that is listed as a post-emergent herbicide to remove unwanted weeds in the landscape. There are several types of Roundup available for use by the home gardener. Each of the formulas is specifically designed for various types of gardens, from flowers and roses to herbs and vegetables. The original formula can be used at any time to remove weeds and undesirable vegetation. There are some things to consider when you use the product prior to planting grass seed.

Active Ingredient

  • Roundup lists glyphosate as the active ingredient that kills most weeds. For the herbicide to have any affect, the seed must have sprouted and the plant must be actively growing so the stomas on the stems and leaves take in the glyphosate and disperse it clear to the roots. Roundup is not selective when destroying plants. Flowers, grass and weeds are all susceptible to the herbicide. Over-spray carried by the wind can be harmful to nearby plants, trees and shrubs.

Application Times

  • The best time to apply Roundup is when there is no wind or rain in the immediate forecast. Rain water can wash the chemical from the weeds and reduce the effects. You have to reapply the chemical for eradication of the weeds. This could damage any grass in the area. Once the glyphosate enters the plant's system, the damage is done. Depending on how long it takes the chemical to reach the roots, the grass or other plants could be dead within days.

Effects on Seeds

  • Since seeds are a self-contained feeding system, the glyphosate in the Roundup has no effect on the seed. Nor will the emerging new sprout be affected. You can sow grass seed within hours of applying Roundup to the weeds in the yard. This process is good only for post-emergent Roundup varieties that do not boast extended weed control. Those products that contain extended weed control will kill the seedlings as they sprout because the chemical is transferred from the soil to the plant through the roots.

Planting Grass Seed

  • For best results when planting grass seed after using Roundup, wait at least seven days after treatment to ensure the unwanted vegetation has been removed from the area. Re-treat the area, if necessary, to remove all the weeds. The package directions also state that the weeds may take longer than seven days to die and that new seeds may sprout after treatment. While you can sow the grass seed after the weeds are treated, waiting about a week lets you know whether the weeds are dead or if you have to re-treat.

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