Q: My pansy beds have lots of chickweed in them each spring. How can I control this pest?
A: When the chickweed has germinated and covered the pansy bed with a thick covering of green, about all you can do is pull it by hand.
I’ve learned from experience that even an extremely careful spraying with Roundup inevitably gets some poison on the pansies…which then die within the week.
Make a note to put a pre-emergent weed killer on your beds next fall when you plant.
This publication has recommendations on the chemicals that might help you.
Weed Control in Pansies