I had always thought my daffodil drifts were “forever,” too, but lately some old naturalized clumps here have fewer flowers than in previous years.
Generally, when plants of any kind don’t bloom it’s usually an issue of either not enough light; too much nitrogen (which makes green, not flowers); too little of the other nutrients they need; or overcrowding (particularly relevant in the case of bulbs). Improperly timed pruning (cutting back too soon, whether with shrubs or bulbs) can diminish bloom as well.
A checklist of causes:
- Are you feeding with high-nitrogen fertilizer (the first number in the N-P-K ratio should be low; high N=no flowers)?
- Did you neglect to feed for more than a year or two? Feed bulbs when they begin active growth, when the green shoots are emerging. Use an all-natural organic fertilizer intended for bulbs. Apply according to label directions.
- Did you cut foliage back too soon last year? (At least 6 weeks of “ripening” time is needed, with their foliage growing and intact, is needed.)
- Is the area very dry? Bulbs need ample moisture when they are in active growth. (On the other hand, a soggy area is harmful to them.)
- Is the area filled with tree roots, or with other competing plants who grab all the nutrients and moisture? Areas under evergreens can be inhospitable, for instance. Dividing may be called for (or transplanting to another, better-suited area).
- Were the bulbs recently planted or recently transplanted? Both can set back the bulbs for a time.
With daffodils (and bulbs in general) there are some additional triggers of diminished bloom, says the American Daffodil Society. Read their full list of possible causes.