How to control weeds in your lawn using pre-emergent herbicides, post-emergent sprays, and cultural practices. Step by step seasonal weed control schedule.
Apply pre-emergent herbicide when soil temperatures reach 55 degrees at a 4 inch depth for three consecutive days. In the Omaha metro, this typically occurs in late March to mid April. Products containing prodiamine or dithiopyr create a chemical barrier in the top 1 to 2 inches of soil that prevents weed seeds from germinating. Water in with 0.5 inches of irrigation within 24 hours of application.
Once dandelions, clover, and other broadleaf weeds are actively growing (typically May), spot treat with a selective broadleaf herbicide containing 2,4-D, dicamba, or triclopyr. Apply when temperatures are between 60 and 85 degrees and no rain is expected for 24 hours. Spray individual weeds rather than blanket treating the entire lawn to minimize chemical use.
If your pre-emergent product does not provide season long control (most prodiamine products last 3 to 4 months), apply a second application in late May or early June to maintain the germination barrier through summer. This catches late germinating crabgrass and summer annual weeds like spurge and prostrate knotweed.
Mow at 3.5 to 4 inches during summer. Taller grass shades the soil surface, which reduces soil temperature and blocks light from reaching weed seeds. Cutting too short is the single most common cause of summer weed invasions. Never remove more than one third of the grass blade in a single mowing.
September through mid October is the best window for killing perennial weeds like creeping charlie, clover, dandelion, and wild violet. Perennial weeds are transporting carbohydrates to their root systems for winter storage, and herbicides applied now follow that flow deep into root systems for a more complete kill. Use triclopyr for tough creeping weeds.
Wait 2 to 3 weeks after post-emergent herbicide application, then overseed bare areas with quality grass seed at 4 to 6 pounds per 1,000 square feet. Filling in thin spots with new grass is the best long term weed prevention. The new grass competes with any weed seeds that survive the herbicide treatment.
In early September, apply a pre-emergent to prevent winter annual weeds like chickweed, henbit, and annual bluegrass from germinating. Note: if you are overseeding, skip the pre-emergent in overseeded areas because it will also prevent grass seed from germinating. You can apply pre-emergent to areas you are not overseeding.
All weed control falls into two categories: pre-emergent (prevents weeds before they sprout) and post-emergent (kills weeds that are already growing). A complete weed control program uses both, timed to the weed life cycles in your region.
The third and most important factor is cultural control: keeping your lawn thick and healthy enough to outcompete weeds naturally. No amount of herbicide will keep a thin, stressed lawn weed free.
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