Timing Is Everything

Can you use the bloom time of forsythia and daffodils to determine when to apply pre-emergent herbicides? Not necessarily, says master gardener Paul James.

Figure A

Forsythia in bloom is a pretty unmistakable sight, and although it's certainly possible that forsythia--and daffodils--in your area do indeed flower at about the time you should apply a pre-emergent herbicide, it's not likely.

"Here in my neck of the woods, forsythia and daffodils often bloom two to three weeks after many of the most common lawn weeds are already up and growing," James says, "so coinciding the application of herbicides with the bloom time of those plants would have no effect on the weeds."

Plus, not all forsythia are alike, meaning they don't all flower at the same time; in fact, the bloom time among forsythia can vary by several weeks. The same is true of daffodils, particularly because there are daffodil varieties that are considered early-, mid- and late-season bloomers, and the differences between their bloom periods can vary by as much as five or six weeks.

"The surest way to determine when to apply pre-emergent herbicides is to carefully inspect the lawn between mid to late winter for any weed growth. When you see a weed, apply the herbicide."

Figure B

Instead of relying on forsythia or daffodils as your cue to apply pre-emergent herbicides, James recommends substituting another yellow, spring-flowering shrub, witch hazel. In USDA zones 4, 5, 6, and 7, these beauties bloom a few weeks before forsythia, which makes them a much more dependable cue."