If you are standing in your garden this spring looking at a clump of healthy green daffodil foliage with no flowers to show for it, the most likely explanation is simple: those bulbs have gone blind. It is a term you will hear used by gardeners to describe exactly this situation, where established bulbs continue to produce leaves year after year but stop flowering. It is not a disease, it is not a sign that the plants are failing, and it does not mean you have done anything wrong. It means the clump has become congested, and that is something you can fix.
When you plant a single daffodil bulb, it does not stay as a single bulb. Over the years it multiplies, producing smaller bulbs around the original. In a well-maintained garden that is a good thing — one bulb becomes five, five becomes fifteen. But left too long without intervention, that underground clump becomes so crowded that the individual bulbs can no longer swell up enough during the growing season to store the energy they need to produce flowers the following spring. The foliage is still there, still doing its work, but the bulb beneath it is too small and too squeezed to bloom. That is what blind means.
The fix is straightforward, but the timing matters. You cannot do it right now while the plant is in growth — you wait until the foliage has completely died back.
In an Irish garden that will typically be late May or June, depending on the season. When the leaves have yellowed and collapsed fully, lift the clump out of the ground. What you will find underneath is not one bulb but a tight cluster of them, pressed against each other. Pull them apart gently by hand — they will separate easily at the natural join between them. What was one congested clump of eight or ten might give you eight or ten individual bulbs, each of a reasonable size. Replant those individually in the autumn, spaced properly so they have room to establish, and the following spring you will have flowers again.
There is one other situation worth considering, and it applies if the daffodils in question are not long-established but were planted more recently. A new planting that fails to flower in its first or second spring is not necessarily blind — it may simply be that the bulbs were on the small side when you bought them. Bulb size matters considerably for daffodils, tulips, alliums, and most other spring bulbs. The bigger and heavier the bulb at planting time, the more energy it contains, and the better the flower it will produce. A small bulb from a cheap multipack will often produce only foliage for a season or two while it builds up to flowering size. If that is your situation, the answer is patience rather than lifting — though feeding the soil well as the foliage dies back, with a high-potassium, high-phosphorus feed or a biochar-based granule, will help the bulb put on size more quickly.