Six years is a long time for a clump of Asiatics to go without being divided, so the decline in the bloom count isn't surprising. When the clump gets to the stage where bulbs are being forced out of the soil, root competition is pretty fierce. The normal advice is to lift and divide them about every 3/4 years - but careful observation of their performance, like yours, is as good a guide as any.

The best time to lift them is just as the foliage yellows & dies back - that way you can see where the clump is (and not accidentally spear too many) and they'll have the longest time to re-establish themselves before starting into growth again. But, if you can't do it then, any time before the clump starts into growth will do. The time to avoid is after shoot growth has started - young lily stalks snap very easily, and pulling the bulbs apart will cause a lot of damage.

Replant them at the same depth as the lowest bulbs you find, and with the same spacing as originally. You'll probably have a lot of spare bulbs at this stage - unless you're deperately keen on this lily, be prepared to dispose of any that are small, damaged, or just surplus (remember, you'll be doing this again in a few years).

When you're lifting a clump is also a good time to amend the soil if it needs it, to improve drainage if that's a problem, incorporate fresh compost, etc.. Don't be tempted to mix strong fertilisers in with the soil around the bulbs. When they're not in active growth they won't use it and it might actually burn them. If you feel that you absolutely have to use it, scattering it onto the surface is best.

Hope this is useful.

Some great advice from kayman. It sounds as though you'll probably have a big ball of bulbs to separate. Be prepared for it to be a rather sow process. You'll have to gradually work the bulbs and roots free from the clump and each other. Sometimes it helps to spray the dirt off with a hose. Replant the biggest bulbs and you'll have lots of "babies" to share with friends or re-plant in another area.

Thank You both so much. I figured they should have been divided a couple years ago but time always seemed to fly by and then it was too late. I will make sure to get it done this year.

Oops! I meant to say slow, evidently the fingers were moving faster than the brain. (again)

Wow, what a gorgeous clump of lilies! The dark green foliage is especially impressive!!!!!