MirelaCarare,
I think it is good advice that daylilies do like a certain amount of a nitrogen boost. You did not say where you are located, so your statement about acting on this advice during the summer might not be the best timing to be adding nitrogen. I suppose the amount and the method would be very important to consider also. I like early spring and fall for adding fertilizer to my plants, but I am in zone 8b. During the hot summer my plants are usually pretty well stressed with the heat and the droughts we have had recently.
Edited to add:
I also wanted to mention that you may have also read that daylilies are very drought tolerant( and they seem to be), but the best thing to improve daylily performance is plenty of water. Some say adequate water is more important to performance than any fertilizer. I think this is probably the most common misconception people new to daylilies have, that they don't need or like much water.
