It sounds like the soil may be too heavy for the root system and they arent able to breath, others will come along and give you great advice about the soil. I always add perlite to my potting soil to make it a little lighter and I've had great success.
Christine

I'm surprised no-one else has responded to this one yet.

Peace lilies can be grown a number of different ways but if you want to grow them in soil, the easiest way to go about it is to buy a bag of orchid mix and then mix it in equal parts with the regular soil and re-pot your plant in that. The trick is to keep the roots moist but at the same time to give them plenty of air around the roots. Moist, not wet (although they do grow wonderfully in semi-hydro or even just water). Water it when the top of the soil feels like it is drying out. Water enough so that you see it draining out of the bottom of the pot.

Peat can be good for your garden but in potted plants, too much of it can cause a lot of problems.

When you do your re-pot, wash all of the original soil off the roots before potting it up and cut off any of the roots that are mushy or broken.

I have one that's been growing completely in water for over a year now, it's on the edge of a pond. It's always grown well and is flowering. But it gets the sprinkler twice a day, so it gets a flush of fresh water regularly. So if you have them in a soil that retains water they should be flushed well regularly. I think it's stagnating water that does them the most damage.

IMHO Peace Lilies like to get to the point of flagging before watering again once in a while.

Seems to strengthen the roots and encourage flowering. Constant wetness makes them 'lazy'.

They are definitely plants that people have a number of differing opinions about. I would never let mine dry out and others say to let them dry enough to start wilting the leaves.

I have some that are grown semi-hrdro, rooted in LECA and they never stop growing new leaves, sending out runners and flowering. They are always kept with the roots in water.

I've seen some really great looking PL's at a local shop that they had washed all of the soil off the roots and placed them in small glass globes with smooth river stones and filled with water, no soil at all. These were some of the fullest Peace Lilies I've ever seen and the whole setup looked pretty cool too. I have some soil grown plants that I'm thinking of trying this on if I ever get the time to do it..

I agree Dellis, I've seen them set up in ponds and growing and flowering really well. That's what prompted me to try one in water. But mine is in gravel in a pot sitting in a pond. And I've seen photos of them in habitat, sitting in water.