Answer: The problem with berries spreading rampantly like this is because they spread by underground runners. Many times you have to control brambles in a bed designated for berries because they grow so wildly. This is usually accomplished with an underground barrier. Try cutting down the bramble (as you have done) and then going to the source of the blackberry (if you can find it, perhaps go to where the woods meet her lawn) and dig down 2-3 feet and put in a wood or metal barrier so the roots can't spread. A little edging would need to be left at a few inches above soil level, because they will "jump" the barrier in the summer....keep an eye out for them, they are very, very aggressive. Short of that, you could just keep mowing the new sprouts down as soon as they appear. Hope this helps, my mother has a Sweet Autumn Clematis that is trying to eat her house so I can sympathize!
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