The Primula genus contains at least 500 species and an almost infinite number of hybrids and cultivars. Most are short-lived perennials, and there are species native to almost every temperate region in the Northern and Southern Hemispheres. However, the most common garden varieties are hybrids, derived mostly from P. elatior, P. juliae, P. veris and P. vulgaris. These hybrids are collectively known as Primula x polyantha. These spectacularly colorful plants are short-lived perennials in zones 5 to 7 but are often grown as bedding annuals in colder or hotter zones. P. x polyantha is the variety that is sometimes forced into early bloom as a potted gift plant.
Cultivated varieties usually carry the common name of primrose, and they generally share a similar shape—low rosettes of dark green leaves with umbrels of colorful flowers that arise on sturdy stalks in spring. They may remain evergreen in the zones where they are hardy. There's a lot of variety in primrose flowers. Some varieties have clusters of flowers on a single stem, while other primulas have one flower per stem, with stems that create clusters of flowers that skim the rosette of leaves.
As garden plants, primroses are generally planted from potted nursery starts in the spring. They can be planted from seeds, but they are slow to germinate and even slower to grow into flowering maturity. Further, the seedlings need special chilling that is hard to accommodate when starting them indoors.
|Botanical Name||Primula spp. and hybrids|
|Common Name||Primrose, polyanthus|
|Plant Type||Short-lived perennial, often grown as annuals|
|Mature Size||6–20 inches tall, 8–20 inches wide (varies by species)|
|Sun Exposure||Part shade to full shade|
|Soil Type||Rich, humusy soil|
|Soil pH||6.0 to 6.5 (slightly acidic)|
|Bloom Time||Species are spring bloomers; hybrids are repeat bloomers|
|Flower Color||All colors except green|
|Hardiness Zones||2–8 (USDA); most hybrids are hardy only in zones 5–7|
|Native Area||Species are found throughout temperate zones|
|Toxicity||Toxic to humans and animals|
Primroses thrive in partial shade and look perfectly at home when planted in large swaths near a tree. If they have to, they can tolerate full sun, but they'll need more frequent watering to remain cool and moist. To guarantee you get the flower color and style you want, buy your primroses while they are in bloom. They should still remain in bloom for several weeks after you take them home and plant them.
Once established, primroses need very little care, other than occasionally dividing the expanding clumps if you are growing them as perennials. Just be sure they get regular water, which shouldn't be a problem in the spring, and some shade during the hottest hours of the day. If you plant them in a suitable site, you should have not problems. They don't even require winter protection.
Primroses will brighten any shady corner. They look especially good massed under a tree or in a natural setting such as a rocky cliff or woodland area. Primroses are a good choice for the north side of a house or as an early spring ground cover under foundation shrubs. Your primroses will blend well with other shade garden plants such as ferns, hostas, and astilbe.
The hybrid primroses prefer a part shade location where they experience some morning sun but shade during the heat of the day. Species types, such as P. vulgaris, do a bit better with full shade.
As woodland plants, primrose prefers moist soil with a slightly acidic soil pH. They also welcome copious amounts of organic matter. While primrose plants like moist soil, most varieties do not like to sit in wet soil and need the well-draining texture that a rich, organic soil can provide. (Both Primula japonica and Primula denticulata can handle wet feet.)
Hybrid primroses are fairly thirsty plants and require regular watering. A good layer of mulch will help retain soil moisture, but they do not like to be constantly soggy. Species types are somewhat more tolerant of wet soils.
Temperature and Humidity
Hybrid primroses are hardy in zones 5 to 7, but are often grown as bedding annuals in warmer and colder zones. There are some species types that are hardy as far north as zone 2. But no primroses are suitable for USDA Zones above 9 and up because they require a winter chill to survive and bloom.
Hybrid primroses need regular feeding with a half-strength liquid fertilizer—a requirement that's common with profusely flowering plants. Species types can be over-fed, however, and do well with just a single spring feeding.
Is Primrose Toxic?
Primula species are mildly toxic to humans, earning a class 4 rating (causing dermatitis reactions). They are slightly more toxic to dogs, cats, horses, and other animals, but not dangerously so.
Symptoms of Poisoning
With humans, skin contact may cause rashes, hives, and other allergic reactions. Pets sometimes experience mild vomiting if the plants are eaten.
- Primula x polyantha : These are the modern hybrid primroses, offering many different bright colors. Most garden center primroses are of this type. They are quite easy to grow. They are hardy in zones 5 to 7, but often grown as annuals elsewhere.
- Primula vulgaris: This is the common wild primrose that is native in most of western and central Europe. It has pale yellow flowers that bloom in April. It is not a common garden plant, but it serves as one of the parent species of the many hybrid primroses. It is hardy in zones 4 to 8.
- Primula denticulata (drumstick primrose): This plant is native to the Himalayas and is hardy in zones 2 to 8. It grows about 1 foot high with a clustered ball of flowers atop a sturdy, upright stem. It is one of the few primroses that is relatively easy to grow from seeds.
- Primula veris (cowslip): This yellow-flowering Primula is native to Europe and Asia but has now naturalized over much of eastern North America. It is hardy in zones 3 to 8.
- Primula kisoana (hardy primrose): Hardy in zones 4 to 8, this species has striking pink to rosy mauve flowers that bloom from April to May. It was originally native to Japan but is no longer found growing wild there.
- Primula japonica (Japanese primrose): This is an excellent species for planting around water features, as it thrives in a moist environment. Growing 1 to 2 feet tall, it blooms with white, pink, purple, or red flowers in late spring and early summer. It is hardy in zones 4 to 8.
It's easy enough to lift and divide primrose plants after flowering. This is the best way to multiply your batch since it guarantees you can maintain specific cultivars.
When starting plants from seed, a temperature between 40 and 50 degrees Fahrenheit is required from sowing to first bloom, which is next to impossible to attain indoors. Growing primroses from seeds is a tricky business that is usually discouraged.
Potting and Repotting
Primroses purchased as potted houseplants that are forced for early blooming can be kept growing almost indefinitely, moved outdoors during summer and back indoors for winter. However, they will soon revert to their normal flowering rhythm, which is to bloom in early spring. But plants can quickly become root-bound unless they are divided or potted up annually into larger pots. Use a standard commercial potting mix when growing primrose in pots, making sure the pots have good drainage. Regular repotting can also prevent excessive fertilizer buildup that can ruin plants.
Primroses are generally pest-free, but spider mites can be occasional problems, especially when the plants are heat-stressed. Less frequently, plants may be troubled by mealybugs, aphids, and whiteflies; they are best treated with non-chemical remedies, such as horticultural oils.
Primroses are also prone to a leaf spot disease, which manifests as brown lesions on yellowing leaves. Remove infected leaves and make sure your plants are getting adequate air circulation.