I am having the same trouble.

Hi, Usually when the foliage of a plant turns yellow it is a lack of an acid fertilizer, or too much fertilizer, too much or not enough water. Not trying to confuse you, but a plant that is yellow is trying to tell you something. I use Osmacote fertilizer on mine and bone meal once a year, also try adding ashes from your fireplace in the winter, it richens the soil, great for all bulb plants. My poor front bed evey winter is covered in white ashes from my fire place, lol. But I get wonderful results from my bulbs year after year.

I hope this helps

Kathy