The genus Primula includes at least 500 species and an almost infinite number of hybrids and cultivars. Most are short-lived perennials. Cultivated cultivars usually go by the common name primrose and are generally of a similar shape – low rosettes of dark green leaves with umbrellas of variegated flowers emerging on stout stems in spring. There is a wide variety of primrose flowers. Some have clusters of flowers on a single stalk, while other primroses have one flower per stalk, with the stalks forming clusters of flowers straddling the rosette of leaves. In the zones where they are hardy, they can remain evergreen.
Primroses thrive in partial shade and look perfect when planted in large clusters near a tree. Some varieties tolerate full sun but need more frequent watering to stay cool and moist. Most prefer partial shade to thrive. To ensure you get the flower color and style you want, buy your primroses when they are in bloom. They should flower for several weeks after you bring them home and plant them.
Once primroses are established they require little maintenance other than occasionally dividing the expanding clumps if you are growing them as perennials. Just make sure they get regular water, which shouldn’t be a problem in spring, and that they have some shade during the hottest hours of the day. If you plant them in a suitable location, you shouldn’t have any problems. They don’t even need winter protection.
The hybrid primroses prefer a partially shaded spot where they get some morning sun but provide shade during the heat of the day. Species such as P. vulgaris do somewhat better in full shade.
As woodland plants, primroses prefer moist soils with a slightly acidic soil pH. They also welcome large amounts of organic matter. While primrose plants like moist soil, most strains don’t like standing in wet soil and need the well-drained texture that rich, organic soil can provide. (Both Primula japonica and Primula denticulata tolerate wet feet.)
Hybrid primroses are quite thirsty plants and need regular watering. A good layer of mulch helps retain soil moisture, but they don’t like being soaked all the time. Species species are slightly more tolerant of moist soils.
temperature and humidity
Hybrid primroses are hardy in zones 5 through 7 but are commonly grown as an annual bedding plant in warmer and colder zones. Some species are hardy to zone 2 in the north. However, primroses are not suitable for USDA zones above 9 and higher, as they require a winter chill to survive and bloom.
Hybrid primroses need to be fed regularly with a half-strength liquid fertilizer—a requirement common for profusely flowering plants. However, species species can be overfed and do well with just a single spring feeding.