Primroses

Sara Williams

Williams is a graduate student with the Department of Horticulture Science. This column is offered as a service of the

Division of Extension and Community Relations and the Department of Horticulture Science, University of Saskatchewan.

Primroses or primulas are spring-blooming herbaceous perennials of low stature, which do well in shady locations with even moisture. Adding peat moss to the soil is recommended; peat moss increases the soil's water-holding capacity and lowers its pH.

For the best effect, use primulas "en masse"; one or two plants alone have little effect on the landscape.

Many are easily grown from seed, which should be sown as soon as it ripens. Some seed will require a cold treatment before germination occurs. If the seed has been stored dry, alternate freezing and thawing in an ice cube tray in a freezer can overcome dormancy.

Some primulas will readily self-seed. Most are easily propagated through division.

The following species have been tried in Saskatchewan with varying success. Saskatoon is located in Hardiness Zone 2. Zone 1 is farther north while Zones 3 and 4 are to the south.

Primula auricula ('Dusty Miller' primrose)

Native to the Alps Mountains of Europe, and reliably hardy in Zones 2-3, the Auricula primrose has mealy green leaves said to resemble a flour-sprinkled miller's apron. The flowers have yellow "eyes" with either yellow, red, lavender, purple, or red petals. They bloom in May. Auriculas have proven reliably hardy for over a decade in Saskatoon gardens with no extra protection. They are more tolerant of partially sunny conditions than most primroses and are easily propagated by seed or crown division. They do not tend to self-seed.

Primula cortusoides (Cortusa primrose)

Hardy in Zones 2-3, the Cortusa primrose is native to Siberia. It has a basal rosette of light green "wrinkled" leaves with attractive pink flowers held above the foliage on 30 cm stems. It blooms in May. Large clumps may be carefully divided by gently teasing them apart, but this is seldom necessary; the Cortusa primrose self-seeds or "naturalizes" very easily, given moist shady conditions. It is one of the primroses least tolerant of hot, dry conditions and will soon wilt if placed in direct sunlight. It is considered reliably hardy. No dieback has been experienced in the author's garden in the decade in which it has been grown there.

Primula 'Assiniboine' (Assiniboine primrose)

This is a hardy hybrid of P. pallasi X P. officinales which was introduced by the late Dr. Frank Skinner of Dropmore, Manitoba, in 1965. It is still available from Skinner's Nursery. Extremely rugged, 'Assiniboine' grows in the open garden or in partial shade. It has peach-coloured petals and a yellow "eye", is about 30 cm high and blooms in May. It over-wintered successfully in the author's garden during the winter of 1987 with no added protection. Further hardiness testing in Saskatchewan is needed, but it seems very promising.

Primula denticulata (Drumstick or Himalayan primrose)

Hardy in the Devonian Botanic Gardens in Edmonton, and also successfully over-wintered by some gardeners in Saskatoon, the drumstick primrose is nevertheless classified as reliably hardy only in Zones 4-5. For this reason it is best planted in a sheltered location in which it will be assured maximum snow cover. Further hardiness testing in Saskatchewan is needed.

The individual flowers are 1 cm in diameter and form rounded flower heads (which are said to resemble "drumsticks") in lilac, violet, or white, on 25 cm stalks. The white-flowered form is supposed to breed true from seed. The drumstick primrose is native to the Himalayas.

Primula sieboldii (Siebold primrose)

A native of Japan, the Siebold primrose is classified as hardy in Zone 4. Only 22 cm high, the flowers are available in white, rose or purple, and are about 4 cm in diameter. Like other primroses, it demands even moisture. This particular one is recommended for pond-side gardens and will withstand more sun than others. The Siebold primrose survived for two years in the author's garden and then disappeared. It would be worthwhile trying again in a sheltered location with dependable snow cover. Further hardiness testing in Saskatchewan is needed.

Primula X polyanthus (Polyanthus primrose)

A large group of hybrids resulting from intercrosses of P.veris, P. elatoir, and P.vulgaris, the polyanthus primroses are supposedly hardy in Zone 3. They have never over-wintered in the author's garden, although they might survive in a more sheltered location with dependable snow cover. (Ironically, they are offered for sale more often locally than any other type.) Further hardiness testing in Saskatchewan is needed.

Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.