I have a Casa Blanca. I am not familiar with Crystal Blanca. However, I find it extremely important to water all trumpet lilies (oriental lilies) very well not only during, but following the blooming period.

I also feed my Casa Blanca with a liquid fertilizer following its bloom, simply because next year's growth and bloom comes from the goodness of its leaves and stalk as they gradually turn brown and wither. All that nourishment is going into the bulb below.

So cutting any of the blooms to put in a vase, or ignoring the plant following its bloom, affects its ability to gather strength from its leaves and stems. Plus, in the Spring, lilies need to be well fertilized as they prepare to grow and bloom later in the season.

I don't know if I am telling you things you already know and are practising. But this is simply my experience.

Lilies should not get weaker. If anything, they should be producing more bulbs to the point where you can divide them.

Thank you, from
Zone 4, British Columbia, Canada

Thanks krakatowa,

I believe I am doing something wrong. I'll follow your system.

I'm doing something wrong too, they are dwindling and getting weaker for me too and they should not be in my climate. There are commercial lily growers here for goodness sake.

I have been told not to water them much and not to fertilize so I will try doing both and see what happens.

I have Bahia Blanca as well as Casa Blanca. Bahia Blanca has been better. More upright, less sprawling. No increase but 4 or 5 years later, it's still doing well, where Casa Blanca is dwindling.