This is a perennial, but is not usually a problem weed. It is included here as is sometimes appears, and is similar to the Chickweeds, to which it is related. It grows in most soils that are moist.
Weedkillers to use:-
See also Common Chickweed, Common Mouse-ear and Greater Stitchwort which are closely related and have similar flowers. Another weed which looks similar to Bog Stitchwort in its early stages is Blinks