You can also use smaller pieces of flagstone, laid on edge like a a curb stone and buried over halfway into the ground, as an edging. But again, use big enough stones on the border, and no edging will be required. Follow the above link for more detail on this issue. Properly laid ...
But the main thing we discovered when we had to finally purchase some to match our other landscaping was that this edging was one of the cheapest options out there for a long-lasting cement edge. They are between $1.69-2.00, depending on where you live for a 2-foot section, and $1 ...