'Thalia' has been grown since 1916 and still has no real replacement. Each 14 to 16 inch stem carries two or three nodding, pure white flowers with reflexed petals, which is why it is called the orchid daffodil. It is lightly scented and flowers late, after most of the trumpets, extending the season by a couple of weeks.
It likes a little more moisture than the big yellows and is happy in light shade under deciduous trees. Plant it in groups of ten or more; a single stem is easy to miss. Leave the foliage to die back on its own and it will come back for decades.
Botrytis (grey mould)
Grey fuzzy mould on petals and stems, worst in cool wet conditions.
Remove affected parts immediately. Improve air circulation. Avoid overhead watering. Apply copper fungicide if severe.
Narcissus Basal Rot
Brown rot starting at the base of the bulb, spreading upward; soft, decaying tissue and stunted or failed growth in spring. Fungal growth may appear pink or white.
Discard infected bulbs. Plant only firm, healthy bulbs in well-draining soil. Avoid hot, wet conditions during summer dormancy and rotate planting sites.
Narcissus Yellow Stripe Virus
Yellow or pale streaks running lengthwise along leaves; distorted foliage and reduced flower size or vigor over successive years.
No cure. Remove and destroy infected plants. Control aphids, which spread the virus, and buy certified virus-free bulbs.