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How to Use Pre-Emergent & Grass Seed

By Jennifer Loucks ; Updated September 21, 2017

A pre-emergent herbicide is a chemical used to control growth of annual weeds by preventing their seeds from germinating. Apply the herbicide to the soil at least one week prior to weed seed germination to establish and be effective. Grass seed cannot be planted in the area until the fall season as the pre-emergent must fully leach out of the soil to allow the grass seed to germinate.

Purchase a pre-emergent herbicide that is rated for use with grass seed and lawn. Some pre-emergent herbicides will kill all vegetation and should be avoided on lawns.

Clear all vegetation from the area being seeded in late winter or early spring. Apply the pre-emergent herbicide to the soil in late March or early April. The herbicide must be applied prior to sowing grass seed as it can inhibit seed germination and growth.

Water the soil with 1/2 inch to 1 inch of water immediately after applying the herbicide to push it into the soil. The herbicide will stop vegetative weed growth at the root level and must be leached out of the soil before sowing the grass seed.

Sow grass seeds in the fall season once the temperatures begin to cool. Rake the soil well to smooth the surface prior to sowing grass seed. Apply a starter fertilizer to the soil to assist with seed germination.

Sow grass seeds using a broadcast lawn seeder to get an even application of seed. Gently water the seeded area and place a light layer of mulch over the seed to retain moisture and prevent seed being washed away or eaten by birds.

Apply lawn fertilizer three to four weeks after seeding the lawn to stimulate lawn growth. The seed should sprout and become established at this time.


Things You Will Need

  • Pre-emergent herbicide
  • Water
  • Starter fertilizer
  • Grass seed
  • Rake
  • Mulch
  • Lawn fertilizer


  • Do not apply more herbicide than the recommended amount on the package. Excessive herbicide can stay in the soil longer and damage the sprouting grass seeds.

About the Author


Jennifer Loucks has been writing since 1998. She previously worked as a technical writer for a software development company, creating software documentation, help documents and training curriculum. She now writes hobby-based articles on cooking, gardening, sewing and running. Loucks also trains for full marathons, half-marathons and shorter distance running. She holds a Bachelor of Science in animal science and business from University of Wisconsin-River Falls.