March in Arizona: Winter Weeds Are Established — Here’s What To Do Now

It’s March in Arizona. Winter rains started in December, and more rain is still coming. That means winter weeds are no longer “just germinating.” Many are established, actively growing, and some are close to flowering.

If you manage residential landscaping, commercial properties, HOA communities, or real estate listings, this is the critical control window.

Common Arizona winter weeds right now include stinknet (globe chamomile), London rocket, filaree, and annual grasses. The University of Arizona Cooperative Extension notes that invasive winter annuals like stinknet spread aggressively and become a significant fire hazard once they dry in late spring. Learn more here: https://extension.arizona.edu/topics/stinknet

At this stage, prevention has shifted to containment and suppression.

What To Do About Weeds Right Now in March

• Treat immediately with post-emergent herbicide. Weeds are actively growing due to continued moisture. This is actually ideal for post-emergent applications because plants are taking in nutrients — and herbicide — efficiently. Treat before flowering to prevent seed production.

• Prioritize properties with visibility or liability risk. Focus first on entryways, sidewalks, parking lots, HOA monuments, and listing properties. These areas directly impact curb appeal, property value, and safety.

• Remove flowering weeds manually. If weeds are budding or blooming, they must be removed before seed drop. Bag and dispose of them. Leaving them on-site allows seeds to mature and spread.

• Plan for a second application. With repeated rainfall since December and more forecasted, staggered germination is common. A follow-up treatment within 2–4 weeks is often necessary to catch late-emerging weeds.

• Apply pre-emergent in cleared areas. After clearing heavily infested zones, applying pre-emergent to bare soil can help reduce additional germination through spring.

• Evaluate irrigation systems. Many Arizona landscapes are still programmed for higher watering frequency than necessary. Reduce irrigation cycles to avoid creating ideal germination conditions.

Property-Specific March Strategy

Homeowners

Walk your yard weekly. Small patches are manageable; large seed-producing patches create next year’s problem.

Commercial Properties

Increase monitoring frequency during active rain cycles. Clean grounds influence customer perception and tenant satisfaction.

HOAs

March is when complaints increase. Visible weeds suggest lack of oversight. Early aggressive treatment reduces costly spring cleanups and lowers fire fuel loads.

Realtors

Listings photographed in March and April must look clean. Landscape condition significantly affects buyer perception and resale appeal, according to National Association of Realtors research.

Why March Is a Critical Turning Point

By late March and April, winter annual weeds begin transitioning toward flowering and seed production. Once seeds drop, the soil seed bank increases, making next winter’s outbreak worse.

Winter weed control in Arizona is no longer about prevention — it’s about stopping seed formation and preventing a larger cycle next year.

If your property has experienced continuous rain since December, assume multiple germination waves have occurred. A strategic, aggressive response now will reduce labor, cost, and fire risk heading into summer.

Schedule an inspection, treat active growth immediately, and implement a follow-up plan before seed production begins.

Author

Deborah Munoz-Chacon

Owner

Sonoran Oasis Landscaping