Answer: In my experience, mondo grass Ebony Knight" (Ophiopogon planiscapus 'Ebknizam') does not require division. (Perhaps the directions were intended for one of the clump forming ornamental grasses instead. Those do benefit from occasional division to maintain vigor throughout the clump. Over time, the center tends to die out leaving a sort of donut shaped plant.) This plant spreads by rhizomes, so you might want to control its spread by digging out the perimeter portions as needed. The resulting divisions can be replanted elsewhere. Also, I should probably point out that in your area (zone 5A, the coldest part of zone 5 and potentially as cold as zone 4 depending on the microclimate) mondo grass would be marginally winter hardy at best, so it might never get dense enough to worry about spreading. I hope this helps.
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