Weeds in groundcover
Can I use a pre-emergent like Preen on a bed of creeping speedwell ground cover that is fully established to minimize additional weeds?
Cuyahoga County Ohio
Pre-emergent herbicides, like Preen, work by forming a barrier in the upper ½ to 1 inch of the mulch or soil where most seeds germinate and kill weeds as they attempt to emerge.
Because these herbicides have no effect on existing weeds, timing the pre-emergent herbicide application properly is critical for success. Because they work prior to weed emergence, applications must occur before weed germination. Any existing weeds should be hand removed. In most cases pre-emergent herbicides should be applied every 2½ to 3 months.