Two species of quite different flowering habit are the most popular for greenhouse culture. P. malacoides produces dainty flowers on fairly long stems almost continuously; P. obconica blossoms in huge clusters the size of a half-dollar. Plants bloom January to May. Colors range from white through pink to reds and lavender.
Seed is extremely fine and best sown on moist sphagnum moss in a flat and enclosed in plastic. Sow P. malacoides April to August; P. obconica March to June. Remove plastic when seedlings appear; transplant to a mix of 1 part soil and 1 part sand in flats. Before seedlings crowd each other in the flat, transplant to 3-inch pots using the same mix.
Make final shift to 4- or 5-inch pots before roots become potbound, using a mix of 2 parts soil, 1 part sand, 1 part well-rotted manure; or equal parts sand and soil with a complete fertilizer. Water freely, especially during summer; primroses wilt badly when moisture is insufficient. Shade is essential during summer.
The foliage of P. obconica may cause severe skin irritation to some gardeners, so handle carefully, especially when transplanting.