Answer: I think it will cover that area quickly and in all honesty I think it is a risky thing to plant and would discourage you strongly. You might be able to control it seeding about by trimming off the bloom stems (annually, for the rest of your life) but the underground runners are irrepressible in my experience. Mowing along the edges will not contain it. Perhaps a barrier several feet deep would hold it, but I would not want to be responsible for being the one who told you that on the day you realize it has gotten loose. (I have heard of it crossing under sidewalks, for instance.) How does your sister contain it? Perhaps that would work for you too. Perhaps another ground cover would work? Vinca minor, lamium, hostas, golden moneywort, and variegated English ivy could all be considered alternatives.
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