not in my experience sadly. They can reduce some insect pests as they are aromatic. but my rosemary has couch grass intermingled with it.

some germinating seeds secrete a chemical that inhibts germination of seeds close by and I cant for the life of me remember what that is called. If I remember I will come back and re post guest.

alleopathy is the name for seeds inhibiting the germination of others. often seeds of different species though some will inhibit there own kind. :o)

was this an exam question? Dont mind if it was It is fun to help.

I am not aware of any plant that inhibits the growth of annual weeds.

can you imagine how much money you'd make. mind i bet the weedkiller companies would buy you out asap :o)

Using your BBC iPlayer, If you go to GQT on Radio 4 and click on this weeks programme, Bob Flowerdew says yes they do suppress annual but not perennial weeds. Apparently they secrete something that deters weeds.

well not in my garden they dont.

not in mine either I've had annual weeding IN the rosemary!