Primula - The Primrose

As we move into autumn so the nurseries and garden centres begin to bring out their polyanthuses and primroses. They’re great plants for for winter colour, either outdoors on even indoors in the case of Primula obconica, but there’s far more to the genus Primula than just these showy hybrids and cultivars.The genus Primula is comprised of around 500 species. They are mainly native of the northern temperate zones, with around 300 species found in China, though some occur in the mountains of Africa, tropical Asia and South America.Polyanthus are not naturally occurring plants but hybrids; most likely between the primrose (P. vulgaris) and the cowslip (P. veris), though their precise origins are unclear and other species, such as P. elatior, may well have been involved. Because of this confusion and the similarity between the many closely related hybrids they are now grouped under the general title of pruhonicensis hybrids, after a now defunct species, P. pruhonicensis, that has been incorporated into with them.Alright, enough of the technicalities; suffice it to say that those plants commonly called polyanthus, Julian primrose anddouble-flowered primrose are now all lumped together in a large hybrid group with a few divisions based on parentage and flower type. The real thrust of this article, however, is not to cover the fancy hybrids but to introduce some of the other, members of the genus, those less extensively manipulated by hybridists.Before going too far I should mention that many of these plants are not widely available in garden centres. If you want ready-grown plants you’ll need to seek out the small specialist perennial nurseries or mail-order suppliers. However, if you’re happy to raise plants from seed then the horticultural societies alpine plant enthusiasts can often help. Of course, seed is not a viable method for propagating most hybrids and cultivars; for these you’ll need to find a plant supplier or obtain some divisions.In common with other large genera such as Rhododendron, Narcissus and Rosa, the genus is divided into groups of species thatshare similar characteristics, and hence usually similar cultivation requirements too. There are 34 of these groups or sections, so you’ll have to excuse me for not describing all of them. Most of the species likely to be grown in gardens fall into the following sections:AuriculaTypified by the common auricula (Primula auricula), this group of about 20 species from the mountains of Europe forms rosettes of leathery leaves, often with a powdery coating. The flowers are usually wide open, nearly flat and are borne at the top of strong stems. They tolerate more sun than most primroses but rarely thrive in warm winters. Some species naturalise in southern areas.The auricula is native to the Alps, Carpathians and Apennines, and reached its greatest popularity in 19th century Englandwhen it became one of the most popular plants for floral competition, particularly in Yorkshire. A huge range of fancy-flowered forms were developed, few of which survive today, though double forms are fairly common. Primula pubescens, probably most widely available as the cultivar ‘Harlow Carr’, is very like an auricula, just not as sturdily built.Primula allionii, a very small species that is barely 5cm high when in flower, is very popular with alpine and rockery enthusiasts, as is Primula marginata ‘Pritchard’s Variety’, a cultivar of a small perennial native to the Cottian Alps, a mountain range between Italy and France. Both have foliage with a distinctive mealy (farinose) coating. These smaller species rarely succeed for any length of time outdoors unless grown in a rockery with perfect conditions. They like a gritty humus-rich soil with some lime and a mulching of shingle chips. They usually do best grown in containers in an alpine house.CandelabraThe candelabra primroses are usually vigorous, strong-growing plants with lush foliage that dies away completely over winter. They have 50cm–1m high flower stems with whorls of flowers, often quite widely spaced, one above the other like the tiers of a fancy candelabra. Most species are native to the Himalayan region and prefer moist, humus-rich soil in partial shade. Some will tolerate very damp soil.The best known species are all quite similar to one another and are inclined to interbreed and self-sow. Primula bulleyana, found naturally in Yunnan at 3000–3200m, has yellow flowers that open late from orange-red buds. The pink-flowered Primula beesiana is from southwest China, while the similarly coloured P. pulverulenta and P. burmanica, are found in southern China and upper Burma. Primula prolifera (syn. P. helodoxa) is again similar, but has bright golden yellow flowers and is found as far south as Indonesia. The deep pink to red-flowered P. japonica has leaves are up to 25cm long with 50cm flower stems and is found throughout Japan and in Taiwan. Primula japonica ‘Miller’s Crimson’ is a very brightly coloured heavy-flowering cultivar.Less common are Primula cockburniana, a late, orange-flowered species from China with flower stems up to 30cm high; Primula × chunglenta, a hybrid between the Asian species P. chungensis and P. pulverulenta raised in 1929 at the Royal Horticultural Society’s Wisley Garden; Primula poissonii, found in Yunnan and Sichuan, China at 2000–3000m with late-opening flowers on stems up to 45cm high; and Primula wilsonii (syn. P. poissonii ssp. wilsonii), which is similar to P. poissonii but larger all round.CapitataeThis group is most often represented in gardens by the type species, Primula capitata, a native of western China, Tibet,northwest Burma and Bhutan. It has rather flat heads of small purple-blue on narrow stems around 30cm high and is very late flowering, often continuing into summer. Its foliage is light green, an effect enhanced by its powdery coating. This is a woodland species that grows very well alongside streams of in any moist woodsy soil in partial shade.CortusoidesThese woodland primulas have spreading roots and long-stemmed leaves. The leaves are usually crinkled and hairy with shallowlobes. They have somewhat bell-shaped flowers and rapidly become dormant after flowering, which enables them to withstand relatively dry summer conditions, though they prefer moist, humus-rich, well-drained soil in partial shade.The most widely grown species from this group is Primula sieboldii, a native of temperate northeast Asia, including Japan.The wild form has purple-pink flowers but-cultivated forms occur in many colours. It is a very dainty little plant that makes a delightful addition to the woodland garden. The effect is reminiscent of the fairy primrose (P. malacoides) often used for bedding but it is later flowering.DenticulataThis group of winter-dormant species is represented in cultivation by the Drumstick Primrose (Primula denticulata), which is found from Afghanistan to Burma at 1500–4500m. It has long leaves with ball-shaped clusters of flowers on strong stems around 30cm high. It is easily grown and often naturalises in temperate gardens. The flowers are usually mauve but cultivars with white, pink or purple flowers are commonly seen and self-sown seedlings often show a range of flower colours.FarinosaeIncluding both European and Asian representatives, this group includes mainly small woodland or alpine species with clusters of tiny flowers on short stems. They generally prefer only light shade. Despite the name farinose, meaning mealy, not all species have the powder-coated leaves that this would suggest.The best known species are Primula clarkei, Primula rosea ‘Grandiflora’ and Primula warshenewskiana, all of which are very small species that quickly develop dense clumps. They are fully dormant in winter and flower in early spring before the leaves are fully developed. All occur naturally in the Himalayan region and often grow best if treated as alpine house plants. Primula rosea ‘Grandiflora’ and P. warshenewskiana, however, are pretty tough and will usually survive quite happily in rockeries, though protection form slugs and snails may be necessary.MuscarioidesOne of the more widely available species, though the only one of this group you’re likely to see in garden centres, Primula vialii, is a Chinese native that in late spring produces flower stems around 30cm high. Sometimes short-lived and not always easy to cultivate, it is worth trying because its flower heads are very distinctive, particularly half open when the purple flowers are topped with red buds arranged like roof tiles. The group name Muscarioides hints at a resemblance to the grape hyacinth (Muscari) and I suppose the flower heads do look a little like very long-stemmed grape hyacinths. This species needs fairly cool winter conditions with soil that is always moist but never wet. It is sometimes monocarpic (dies after setting seed) and is usually raised from seed because divisions often fail to grow under less than ideal conditions.NivalesNivales means "of the snow", so it’s not surprising that Primula sinopurpurea, a southern Chinese primrose with nearly smooth leaves up to 35cm long, should be found in alpine meadows. Its flowers are deep pink and borne on 30cm stems that grow to 1m high as the seed ripens. The species from which the group takes its name, Primula nivalis, comes from the harsh climate of central Asia and does not take kindly to mild winters. It needs dry conditions in winter when dormant and moisture in spring and summer when active.PetiolaresOnly two species from this group, Primula edgeworthii and P. whitei (syn. P. bhutanica), are generally seen in cultivation. Both are spring-flowering natives of the Himalayas with powder-coated leaves and short stemmed flowers. They are favourites of alpine and rockery enthusiasts and like Primula allionii and P. marginata mentioned earlier prefer alpine house conditions and can be tricky to grow outdoors. Primula edgeworthii has soft yellow flowers, while those of P. whitei are mauve-blue.SikkimensisThe species in this group are strong growers and have very tall flower stems. Those of the giant cowslip (Primula florindae) from southeastern Tibet can reach 90cm high. Unlike the candelabra primroses, the flowers are usually only borne only at the top of the stem rather than in whorls along it. The flower colour is variable and includes all shades of yellow, orange andred. This may be because the garden forms are hybrids rather than the true species. Primula sikkimensis, which is found in various forms through much of the Himalayan region at 3300–4400m, is large-leafed and late-flowering. Its flowers are usually bright yellow, and although I haven’t seen them much over 60cm, the stems supposedly reach 90cm high. The Himalayan cowslip (Primula secundiflora) comes from the same area but its foliage is far more foxglove-like and its flowers are pinkish purple.SoldanelloideaeYou’re only likely to see one species from this group, and even that’s pretty rare. Primula flaccida (syn. P. nutans Delavay non Georgi) is a native of southwestern China where it occurs at altitudes up to 3500m. Its flowers, mauve to purple and slight downward facing, open from head reminiscent of those of Primula vialii and are slightly scented. The leaves are upward facing and nearly as high as the flower stems. Primula flaccida prefers woodland conditions and becomes dormant soon after flowering.VernalesThis group of mainly European and west Asian species includes the parents of the modern garden primrose and polyanthus. Cowslips (Primula veris [syn. P. acaulis]) and the similar but taller-stemmed oxlips (P. elatior) are spring-flowering species found from Britain to central Asia. The true species have soft to bright yellow flowers, downward facing for cowslips and usually upwards for oxlips, but cultivars occur in a range of colours. Both species have a pleasant soft scent. Primula algida, from the Caucasus and the mountains of Turkey and northern Iran, resembles the cowslip but seems to be unscented.The common primrose (Primula vulgaris) more closely resembles the garden polyanthus in leaf shape and general form. However, it only bears one of its pale yellow flowers per stem, or rather the stems is very short and hidden in the foliage so giving that appearance. The tall, multi-flowered stems of the polyanthus show the influence of oxlips and cowslips, but their flower shape is pure primrose. Primula vulgaris var. sibthorpii is a rare primrose variety, sometimes listed as a species (P. sibthorpii), that has mauve-pink-flowers.So there’s far more to primroses than just your everyday poly! Indeed, the many and variable species could make a very interesting garden just on their own, though of course they look much better with a few of their woodland and alpine friends.Raising Primula from seedAs Primula seed is best sown as fresh as possible I recommend sowing as soon as you get it. That may mean providing warmth in winter or cool shade in summer, but either way you’re sure to get better results than delaying sowing, which can only resultin a lower germination percentage.Because of the short viability period don’t purchase seed until you intend to sow it and don’t buy more than you can use immediately. Primula seed, especially that of the fanciest hybrid polyanthus, is often very expensive. The price of even the smallest commercial packets can be quite daunting.Use a very finely sieved high-humus seed-raising mix. Either a peat- or bark-based mix will do. Having a finely sieved mix is important because the seed is very small and the seedlings are not vigorous. They will suffer if they have to push their way up through heavy soil mix.Sow the seed reasonably thickly and don’t cover it with soil; just moisten it in very gently and cover the seed tray with a pane of glass and a couple of layers of newspaper for shading. If the potting soil dries out, water it by soaking the seed tray in a shallow basin or tray rather than watering from above — you don’t want to wash the seeds around.The key to success with primula seed is to keep everything cool and moist. Keep the seed tray at around 12–20°C and well away from any hot sun. Once the seed has germinated you can remove one of the layers of newspaper and wedge up the glass with stones or small pieces of wood to allow the air to circulate. After a week or so replace the glass and newspaper with a couple of layers of shadecloth draped over the trays. Although the seedlings need light and air to harden off, on no account should they be exposed to full sun or drying winds.A shade house or fernery provides ideal conditions for growing on the seedlings. Don’t be in a hurry to prick them out; they transplant well even when quite large but damage occurs if they are handled roughly when small. If you feel the seedlings may be suffering from being in the seed trays too long, thin them out a little and apply some dilute liquid fertiliser.When they can be safely handled, plant the seedlings into small pots or filled with good quality potting mix. Add someshort-term slow-release fertiliser and a quick acting general fertiliser. Fancy hybrid primulas are heavy feeders that benefit from regular liquid feeding.Getting consistent results with primula seeds requires some experience. It’s very easy to overwater the seedlings or keep them too humid, causing them to damp off or rot. Just remember to keep everything cool, feed the seedlings well and don’t rush.

Comments? Questions? Email Here

© HowtoAdvice.com

How to Advice .com