Primroses (Primula species) are native to the northern hemisphere. Primroses are also known as polyanthus and cowslip. Primroses mainly bloom during the spring and are favored by some species of butterflies.
Primroses are perennials with heavily veined, toothed- or scalloped-edge, dark green leaves forming clusters of closely crowded leaves from a very short stem near the ground surface (basal rosette). Some primrose species produce flowers tucked among their leaves, and others bear flowers in clusters. Its five-petaled flowers are tube-shaped and open into funnel shapes or flat discs with each petal notched at its tip. Primrose flowers come in a variety of colors, including yellow, white, pink, lilac and purple.
Most primrose species like growing in a woodland garden setting in dappled shade in locations with cool summers. Primroses prefer moist, rich, well-drained soils. "Bog" primroses, such as Primula japonica, prefer damper conditions and naturalize in stream-side locations. Propagate primroses by division of clumps when dormant (not actively growing or flowering). Divide clumps of primrose when they are overcrowded. Primrose hardiness varies by species, with some hardy in USDA zones 3 through 9 (Primula auricula) and some less cold hardy, growing in zones 8 through 10 (Primula verticillata).
Primroses look lovely in massed beds, containers or borders. They are useful in moist woodland settings. Primula height varies by species, growing from under a foot up to 2 feet tall, with an 8-inch to 2-foot spread.
Primula auricula is a yellow primrose and usually fragrant. It needs moderate levels of moisture and is shallow rooted. Auricula primrose blooms from spring to midsummer.
Primula chugensis has whorls of fragrant, red, tube-shaped flowers with orange petals.
Florinda primrose (Primula florindae) grows in zones 6 through 8 and forms clusters of up to 40 yellow, fragrant flowers on strong stems with broad, glossy leaves. Florinda primrose prefers damp locations.
Primula vulgaris, or English primrose, looks good in mass plantings and forms tufts of green leaves and pale yellow flowers. English primrose tolerates drier soils than other primroses and is considered easy to grow.
Primroses are bothered by slugs and spider mites. Slugs prefer moist locations (like many primroses). Keep slug-prone areas weed and litter free to reduce their populations. Shallow containers (such as jar lids) placed at ground level can be useful for trapping slugs. Control spider mites by spraying plant leaves with a solution of 3 tbsp. dishwashing soap mixed with 1 gallon of water. Reapply once a week until mites are eliminated.