The effect of nitrogen on flowering is not simple.
It is common knowledge that excess nitrogen delays flowering and scientific research confirms that for many plant species. But it is not necessarily simply a delay in flowering.
Much of that research has been done with annuals.
Most plant species, both annuals and perennials cannot flower under normal conditions until they reach a particular size; they need to become mature or adult. As well, the larger the plant the more flowers (and therefore seeds) it produces.
When an annual species is growing in poor conditions (low nitrogen, for example) it will flower soon after reaching its minimum adult size. When it is growing in luxuriant (or optimum) conditions it will not flower at the minimum size but will grow larger than the minimum before flowering. The goal with annual species in a garden is to have them start flowering quickly and to keep flowering as long as possible. It is not considered a good thing for them to delay flowering even if they might produce more flowers in the long run because they may not have enough time to produce large enough numbers of flowers to make-up for the delay before winter arrives.
Perennial species, such as daylilies, also need to reach a minimum size to be able to flower. But perennial species often flower at specific times of the year. Providing them with high nitrogen allows them to reach flowering size sooner (fewer years or months) and to produce more flowers and it probably allows them to be more likely to rebloom.
I grow several daylily cultivars that have not flowered for many years. I have one that has never flowered since I bought it 12 years ago. It does not flower because every winter it is set back and so it has never managed to become large enough to reach its adult/mature size. The same is true for the other cultivars.
Two of my slowpokes are Munson cultivars; one is 'Borgia Queen' and another is 'Chinese Cloisonne'. Another slowpoke is 'Lady Blue Eyes'.
@Kabby, How many fans is 'China Dawn' and how many is 'Wild Child'?
