Hi Central CT Gardener,
I've never heard of that.* Daylilies, oriental lilies and asiatic lilies all are members of the Liliaceae family aka lily family.* Daylilies belong to the genus Hemerocallis.* Asiatic lilies and Oriential lilies belong to the genus Lilium.* They are related but are not the same.* Daylilies grow from fibrous roots that have tubers attached that store food and true lilies (Asiatic, Oriental, onion, hyacinth) grow from bulbs where the food is stored.*
The only thing I can think of as to not plant them together is to space them far enough apart for the Asiatics and Orientals to multiply.* I grow both together, but spaced far enough apart for the faster multiplying bulbs of Asiatic and Oreintal lilies to have space.* That way I only need to dig and replant the bulbs of the Oriental or Asiatics every 3 to 5 years.*
Hope that answers your question.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.