This article give a good overview of the growing needs and care of Daylilies.
Here is a great article that will help you with soil amendments to ensure a good environment and well drained soil for plant health.
I would also encourage you to have a soil test preformed to determine what may be going on in your soil.
Your County Extension Office can help you with a soil test for a few dollars.
Here is a link to help you locate your nearest office.
That could be a complex answer, meaning it may be a combination of factors or the reasons could differ from why one bulb kind failed to why the next failed. Maybe you could give us a bit more info...? Like are you planting in the ground or containers? If in the ground, what type of soil do you have - sandy, hard clay, etc? Are the bulbs rotting before they grow and bloom the first time or do you mean they are rotting after the initial season and not coming back year after year? And there are lots more specifics that may be the cause(s)...planting at the wrong time of year, site location may not have ideal conditions, maybe something as simple as the specific variety does not grow well in your area. There really is a very long list of things that may be contributing to your bulbs rotting but I'm sure we can help, at least for future successes.