Bellis perennis 'Prolifera', the hen and chickens daisy, is an old cottage-garden curiosity: a proliferous sport of the common English lawn daisy in which each double, pompom-like flowerhead sprouts a ring of smaller satellite flowerheads directly from its base, on tiny stems of their own — the 'hen' surrounded by her 'chicks'. Unrelated to the succulent houseleeks that share the common name, this is a small, low-growing herbaceous daisy grown for the novelty of the effect as much as for garden color, a fixture of historic European cottage and edging borders for centuries.
It is usually grown as a biennial or short-lived perennial for cool-season bedding, edging, and containers, and needs the same easy care as any English daisy — moist, fertile, well-drained soil in sun to part shade. The proliferous trait doesn't reliably come true from seed, so division of an existing plant, rather than sowing, is the dependable way to propagate more true hen-and-chickens daisies. Deadhead regularly to prolong bloom and keep the plant from putting energy into non-true seed instead of more flowers.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.
Crown Rot
Lower leaves yellow and wilt; the base of the rosette turns brown and soft, sometimes with white fungal threads at the soil line. Plants collapse in wet conditions.
Remove and destroy affected plants. Improve drainage and avoid overhead watering. Do not mulch directly against the crown. Space plants for airflow and avoid replanting in the same wet spot.