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California Lawns Ready for Pre-emergent Herbicides

by Gabby Hyman, All About Lawns Columnist

Early March is the best time to apply pre-emergent blockers in California if you want to defeat crabgrass, clover, or goosegrass in your lawn this summer. While most broadleaf weeds germinate later in the spring, crabgrass seeds arewell into their sprouting cycle as soon as soil temperatures climb into the 53-58 degree range. You may want to invest a few dollars on a soil thermometer to make sure you hit weeds at the perfect time.

Goosegrass typically germinates two weeks later than crabgrass, so plan accordingly and read pre-emergent weedkiller labels carefully to make sure you're treating the right seeds at the right time.
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Applying Lawn Pre-emergents Scientifically

"The key to any pre-emergent weed treatment is timing," says Bob Cline, golf course superintendent at Sacramento's William Land Golf Course. "If you wait too long, pre-emergent chemicals are ineffective on visible weeds and you might be dealing with herbicide degradation if you apply it too early."

Cline recommends buying a soil thermometer that costs between $8 and $15 and using it between March 1 and March 20 in California. Soil thermometers have a depth line to indicate precisely how far they must penetrate your lawn to gather an accurate temperature. Soil thermometers look like kitchen meat thermometers with a long, sharp probe and a circular readout on the top.

Pre-emergent weed chemicals don't kill seeds; they coat them to prevent sprouting. Use these weed retardation applications on a yard that is already established because some of them can block the germination of grass seeds that you might be putting down to fill in or over seed your lawn. The length and effectiveness vary by brand, the amount applied, the soil texture, moisture, and temperature. Problems with runoff or leeching are minimal and microbes in the soil eventually break down the applications. 

About the Author
Gabby Hyman has created online strategies and written content for Fortune 500 companies including eToys,, Siebel Systems, Microsoft Encarta, Avaya, and Nissan UK.

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