Hi Redroses--it really depends on what zone you're in. They should be covered in all zones except the very warmest if they're at the base of the stems, attached to the roots. Itohs can actually go a bit deeper than herbaceous but I'd play it safe and cover them with up to 2" of soil if you're in a cold zone, less if you're warmer. I'm zone 4b and mine are under 2" of soil. Itohs do put out buds higher up on the stems, you don't want to bury them that deep but some people have had success with cutting the stem below the bud and planting it. Those buds are wasted in the colder climates, they'll completely freeze and won't grow the next spring, so an attempt at getting a new start on a plant is a good thing...

Thanks Lizbest, wow glad you told me all about that, this is my 1st itoh, Im in zone 6, kansas.Ok, l will cover it with 2 " soil. Thanks.