Funny, I'm noticing the same thing as I grow out my gray. My formerly fine, colored hair that textured and clumped fairly easily -- the gray part is grizzly and coarser, not as curly, more dry, and wants to separate and frizz.
Probably the co-wash you are using is fine, but you may want to raise the moisture/emollient bar a bit on your leave-in, either by adding something like one of the following:
- Karen's Body Beautiful Hair nector
- Jane Carter nourish & shine (great on wet ends over condish)
- a little (pea-sized) shea butter softened with a few drops of oil
- Qhemet Burdock Root Butter cream
Also I cleansed my hair last week with a clay treatment (rhassoul clay, water, ACV, honey) followed with KBB hair milk and Knot Today
, and my grays were noticeably silkier and clumpier when dry.