Will Kentucky Bluegrass Spread After Pre-Emergent?

Kentucky Bluegrass (KBG) is known for its ability to spread and fill in lawns due to its rhizomatous growth habit.

However, the application of pre-emergent herbicides raises questions about their impact on this grass’s spreading ability.

Pre-emergent herbicides are designed to prevent weed seeds from germinating, but they can also affect the germination and growth of desirable grass seeds if not used correctly.

Will Kentucky Bluegrass Spread After Pre-Emergent?

The spreading of Kentucky Bluegrass after the application of pre-emergent herbicides depends on several factors, including the type of pre-emergent used, application timing, and the existing maturity of the KBG lawn.

Impact of Pre-Emergent on Kentucky Bluegrass

  • Existing Lawns: For established KBG lawns, pre-emergent herbicides generally do not inhibit the grass’s ability to spread through rhizomes. These herbicides target seed germination, so the vegetative spreading of mature grass is not affected.
  • New Seedlings: If you plan to overseed a KBG lawn, applying pre-emergent herbicides can inhibit the germination of new KBG seeds. It’s crucial to time the application correctly or choose a product that is safe for use with new seedlings.

Best Practices for Pre-Emergent Application with KBG

  • Timing: Apply pre-emergent herbicides in early spring before weed seeds germinate. If overseeding, wait until the new KBG seedlings have been mowed 2-3 times to ensure they are established enough to tolerate the herbicide.
  • Product Selection: Some pre-emergent products are formulated to be safe for use around the time of seeding. Look for products labeled as safe for new grass or specifically designed for use with KBG.
  • Follow Label Instructions: Always adhere to the product label for application rates and timing to minimize any potential negative impact on KBG spreading.

FAQs on KBG and Pre-Emergent

Can I overseed KBG after applying pre-emergent? It’s recommended to wait until the effectiveness of the pre-emergent has diminished before overseeding KBG, typically several months after application.

Will pre-emergent completely stop KBG from spreading? No, pre-emergent herbicides primarily affect seed germination. Established KBG lawns will continue to spread through rhizomes.

How can I encourage KBG to spread in my lawn? Regular mowing, proper fertilization, and adequate watering encourage KBG to spread. Aerating compacted soil can also promote rhizome growth and lawn thickening.

In Summary

  • Pre-emergent herbicides are unlikely to inhibit the spreading of established Kentucky Bluegrass lawns but can affect the germination of new seeds.
  • Proper timing and product selection are crucial when using pre-emergent herbicides in conjunction with seeding or overseeding KBG.
  • Established KBG lawns can continue to spread and fill in areas after the application of pre-emergent, provided the herbicide is applied correctly and the lawn is well-maintained.

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