I have always heard this but i have a pile of grass clipping that is in a washout to keep it from eroding any more and after 3 years still have no bermuda grass coming up only crabgrass on a occasion. It really depends on what kind of clippings you use mine has a wide variety of different grasses in it including bermuda.if you use grass clippings for mulch is a good way to introduce unwanted Bermuda grass to your garden.