There are over 400 species of primulas, or primroses, found in habitats ranging from marshlands to alpine slopes. Primrose foliage forms rosettes – clusters of leaves in a circle - that grow close to the ground. The flowers grow either clustered together among the leaves or on stalks in umbels, whorls or spikes. Primroses are ideal for a waterside garden, shade garden, or rock garden and some varieties can be used as bedding plants.
Basic Care for Primulas
Primroses tend to prefer climates with cool summers — plant in partial shade to avoid the intense summer heat. Many primroses will take full sun, but usually require constant or at least good moisture levels.
As a rule, primroses do not like to dry out. This does not mean that they like to be water-logged. Many will survive in wet sites, but they need good drainage. To ensure good drainage, add coarse gravel (grit) or sharp sand to the soil.
Primroses do not like windy sites where they will dry out.
Primroses tend to like nice, loamy soil. Mulching your plants with shredded leaves will ensure that there is a rich supply of humus – rich, broken down organic matter.
Amending your soil with well-decomposed compost will improve your soil’s moisture retention and will create a nutrient-rich environment
Fertilize your primroses in the early spring with either a balanced fertilizer or a bloom booster (10-10-10 or 5-10-5). Double-flowering primroses are heavy feeders.
After double primroses have flowered, fertilize them with liquid fertilizer to ensure healthy leaf growth. These plants exhaust themselves when flowering and do well with an additional mulch of composted manure after flowering.
Many primroses multiply freely. Divide the plants in the fall or early spring by digging up the rosettes and pulling them apart. Make sure that the transplants are well watered for several weeks.
The roots of primroses develop from the crown of the plant (the base of the rosette). Plant them at the level of the crown and mulch around them with shredded leaves, well-decayed compost or manure, making sure not to pile the mulch on the crown.
The primroses that you buy from your florist around Mother’s Day (polyanthus primroses) are generally used as annuals. They will flower for up to 8 to 10 weeks in April and May if you deadhead them. Like many other primroses, they like good moisture and rich soil. If you would like to grow them as perennials, plant them in partial shade to shade.
Some Easy Varieties for your Garden
Primula veris (cowslip) – An evergreen to semi-evergreen perennial, it has nodding, fragrant, yellow flowers that appear April into mid-May. Cowslips like very sunny locations. In the wild, they grow in fields and by the woodland edge. They like moist, well-drained, humus-rich soil and can tolerate very damp soil if they are in full sun. Primula veris ssp. macrocalyx has large, sulfur, yellow flowers and Primula veris ‘Katy McSparron’ has lovely, double, upright flowers.
Primula japonica (candelabra primrose) – This is a deciduous perennial from Japan. Its long stems bear anywhere from 1 to 6 whorls of red-purple to white flowers from mid-May into June. It prefers to grow in moist, shady places. In the NYBG Rock Garden, it is growing right on the stream’s edge.There are a number of species called candelabra primulas. Primula bulleyana is another candelabra primrose with orange flowers.
Primula vulgaris (wild primrose) – An evergreen to semi-evergreen perennial, it has clusters of 3 to 25 pale, yellow flowers in early spring. They prefer partial shade but are fine in sun if the soil is kept moist. Wonderful for a wood's edge, the clumps can be divided in September or in early spring before they flower. Good cultivars include Primula ‘Quaker’s Bonnet’ (double, lavender), Primula ‘Cottage White’ (double white) and Primula ‘Marie Crousse’ (double violet).
Primula denticulata (drumstick primrose) – This is a deciduous perennial. It is an early bloomer, with flowers ranging from white to purple appearing on thick stalks in April. The flowers are clustered tightly in umbels that look like little drumsticks. This primrose is easy to grow, is very floriferous and increases well. It likes moist, rich soil in partial shade to full sun. Good garden soil will be fine, as long as it does not get too dry.
Primula sieboldii (Asian woodland primrose) – These flowers range from white to crimson with all shades of pinks and purples in between. Not only do they come in nice colors, they come in nice shapes – bells, stars and snowflakes. They flower from April into May. In the wild they grow in moist meadows and in woodlands. They often go dormant in the summer and prefer to grow in a cool, shady spot.