Lynne, I have all my hardies planted in dollar store dishpans, both round & oblong. I'll put a layer of fertilizer (Osmocote green cap 14-14-14) mixed half/half with Colorburst fertilizer (I get both at Home Depot) on the bottom, then dirt, the plant, & gravel on top. I am probably putting too much fertilizer in the pan 
If you have a particularly stubborn lily, plant in a pot with a couple of holes for gas exchange. Another fertilizer I'll use is the Jobe's Tomato spikes when I don't want to mess with pulling the plant out of the pot.
Hmm, you have me thinking about that whole gas exchange....maybe that's why they all got buds when I divided them. They liked the air. I can make holes in them. Small scissors....and I might try a couple more tabs, or some pantyhose buried with some osmocote. Only thing about the osmocote is, this year, for some reason, it seems to be kicking the cyanobacteria in to full blown blooms. Never had it before this year, and only in the containers with it, in a plant or the Tea Cup. But I have been unable to get rid of it, even with more oxygen and water changes. It smothers the small pygmy lily pads, and the parrots feather FAST. But I will give that a try.
Meanwhile, the Trickett has finally started in again. This pic was from yesterday, or the day before, and as you can see the pads are HUGE. They are well over 13". There are NINE buds on it, more than it's ever had. This one got 6 tabs over the span of a week, then it went crazy. See the lemon mist, not one bloom. Sad.
Anyway, I am so glad it recovered from repotting it. And it seems as strong as ever. In fact, the most buds it ever had before at one time were 7, so it's actually doing better than before.
Here it is before-or right when I repotted it;
And the other day;
