Pre-Emergent Herbicide
An herbicide applied to soil before weed seeds germinate. Pre-emergents create a chemical barrier that prevents seedling roots from developing. They don't kill existing plants — they only prevent new ones from sprouting from seed.
Pre-emergent herbicides work by creating a treated zone in the top layer of soil. When a weed seed germinates and its root begins to grow, it contacts the chemical barrier and cell division is disrupted, killing the seedling before it can establish.
Key principles:
- Pre-emergents must be applied BEFORE seeds germinate. They have zero effect on established plants.
- They must be watered into the soil after application (½ inch of irrigation) to activate the barrier.
- They prevent ALL seed germination — including grass seed. Do not overseed within 8–12 weeks of application.
- The barrier is disrupted by soil disturbance — do not aerate or dethatch after application.
Timing: For spring crabgrass control, apply when soil temperatures reach 50°F at a 4-inch depth — typically 2–4 weeks before forsythia blooms.
More on Pre-Emergent
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