What can I do to make sure crabgrass preventing chemicals actually work?
There are several things that can go wrong with crabgrass preventer application. An unusually wet season can cause the chemical to wash out of the soil. Failure to water it in promptly can allow it to degrade before it ever works into the soil. An application too early in the season can wear out before the crabgrass stops germinating. (Some crabgrass preventers are effective for only 8 weeks or so, whereas crabgrass seeds may germinate until the end of summer). On the other hand, if you wait too late in the season to apply it, crabgrass seedlings may become established before the herbicide is effective. Be certain to apply the crabgrass preventer before the soil temperature reaches 55 F in spring. On south-facing slopes and near driveways or sidewalks, this may happen early in spring. One cue that many gardeners use for timing crabgrass preventer applications is when forsythia is in full bloom. Soil temperature measurements are more precise, but the bright golden forsythia blossoms serve as a good reminder.
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