Getting Started with Primroses

by Dee Peck

The Primula is probably one of the best known plants throughout the world, and yet the average gardener is barely acquainted with even the commonest kinds. Somehow they have acquired the reputation of being exotic and consequently very difficult to grow. Many of the loveliest are exotic and impossible to grow away from their native terrain, but many others can be grown by the expert gardener, and a generous number will flourish even under the hand of the beginner. Here we will deal with the last category and add a sprinkling of the more difficult for those who relish a bit of challenge.

Most of the four hundred or so species of primroses are hardy perennials and are scattered extensively throughout all parts of Europe, Asia and North America. Oddly, only one species is found below the equator, Primula magellanica of South America. Probably the greatest number are native to Asia and were introduced to the western world by plant explorers of the last century such as Farrer and Kingdon-Ward.

With few exceptions, primroses share the same cultural needs: a rich humusy soil, good drainage, ever present moisture, and moderate amounts of light-the need for each depending upon the degree of the others. For example, if your primroses are in shade, moisture requirements are lower than if they are in the sun for part of the day. If your soil is sandy and fast draining, watering must be frequent, more so than if your soil is a humusy loam. Fortunately all these factors can be modified, as we shall see.

The name Primula springs from the Latin word “primus”, or “first”, signifying the plants’ early appearance. The very first to appear in most areas is Primula denticulata, close on the heels of the last snow, and occasionally caught by it! In very early spring, this primrose emerges from swelling rosy buds that remained, barely visible, when the foliage of the previous summer died down. A sphere of blossoms opens even before the stem elongates. The leaves expand as the stem rises slowly, usually to about ten inches in height. The bloom period is three weeks, and bloom color is usually pale lavender. However, forms are available in pure white, purple, pink, and red-all with a white eye. Self-sowing is common, and it is a good idea to pull and discard unattractive colors before they seed. Good colors can be allowed to seed, and can also be easily divided after flowering, in the following manner. Carefully lift the clump, shake gently to remove soil, and carefully separate the crowns. Trim the roots of each division lightly, remove dead leaves and spent blossoms, shorten the leaves by about one half, and replant in rich, well drained soil. Make sure the crown is at soil level and carefully spread the roots, firming the soil about them. Some dilute liquid fertilizer at this time will help counteract the shock of transplanting. Care must be taken that the divisions never dry out. Water religiously until established, and shade if necessary. This method of division can be used for most primroses and will increase choice colors rapidly.

Although it is one of the easiest primroses to grow, it is important that Primula denticulata be well-drained in winter. It has rather heavy, thong like roots, which, along with the crown, will rot in standing water. It prefers a shaded position but will tolerate more sun if planted near a large rock for shade and a cool root run. A stone mulch is also excellent. It promotes drainage, cools the soil and conserves moisture. Primula denticulata is not pretty when bloom is over. The foliage has enlarged to foot-long cabbage-like leaves and the tall stems are topped by untidy seed heads. An attractive solution is an inter-planting of deciduous ferns. The uncurling fronds appear after the flowers of the primroses are gone. This same camouflage can be used with other early flowering primroses.

From late March to early April the “bird’s eye” or farinose primroses appear. The type Primula farinosa, is a tiny three-inch lilac-pink beauty covered with silvery meal. Primula frondosa is almost identical, but somewhat larger. Primula rosea is a glamorous cousin, tiny and a glowing rosey pink. It needs more moisture and thrives near running water. These last two are somewhat more difficult, but P. farinosa and P. frondosa are well worth trying. They want the same culture as P. denticulata, and especially love the gritty, humusy stone mulch.

The vernal primroses arrive at the height of spring. They are the ones which most of us know, and are the easiest of all to grow. The true “primrose” is the wild primrose native to the British Isles, Primula vulgaris. Its pale yellow blossoms are borne singly on short stems that rise just above the foliage. Crosses with its Turkish counterpart, the pink P. sibthorptii, have yielded hybrids in an endless array of colors; pink, rose, pale blue, red, white, orange, bronze and deep velvety purple. These hybrids are properly known as P. acaulis.

Also growing wild in Britain and much of the continent are the cowslip, P. veris, and the oxlip, P. elatior. They are not flashy beauties, but have a quiet charm and are of special interest because they, crossed with P. vulgaris (or P. acaulis) are thought to be the progenitors of the fantastic hybrid polyanthus primroses.

The polyanthus primrose (Primula x polyantha) is a hybridizing triumph. It exists in every color, some brash and brilliant, some pale and subtle, some so deep a purple as to be almost black. All carry a cluster of blossoms on a six to eight-inch stalk. There are many forms, from charming miniatures to giants with sturdy stems and massive flowers. There is ‘Jack-in the Green’, an old form with a green ruffled collar about each blossom. Some are hose-in-hose, some double.

The last vernal primroses we will talk about are Primula juliae and the P. x juliana hybrids. Primula juliae is a low plant with tiny half to three quarter inch kidney or heart-shaped leaves and luminous wine red blossoms carried singly on short red stems. It spreads into mats by means of a creeping rootstock rather than multiple crowns. A striking effect can be achieved by interplanting P. juliae with Chionodoxa, Scilla, grape hyacinths or early flowering miniature pale yellow daffodils.

Crossed with Primula vulgaris, Primula juliae has produced the hybrid line of Primula x Juliana. The best forms have P. juliae’s small size, and have acquired the best P. acaulis colors. Some have single blossoms, and some have umbellate clusters. Among the best are: ‘Wanda’, crimson-magenta; ‘Pam’, brilliant red; ‘Jewel’ crimson; ‘Schneekissen’, white; and ‘Marguerite’, yellow.

The vernal primulas, unlike the deciduous denticulata and farinosa, retain their foliage throughout the summer and even into the winter. Watering is very important as the leaves can be badly disfigured by red spider and the plant weakened in conditions of drought. For the same reason, partial shade and rich moisture retaining soil are essential. If grown under sunnier conditions, as much humus as possible should be incorporated into the soil. Vernal primroses multiply rapidly and should be divided every two or three years, as described under denticulata, and the hard center portion of each clump discarded.

While all this activity has been going on in the woodland and its borders; in the rock garden the Auriculas have been coming into their own. The distinguishing characteristics of the Auriculas are their thick succulent leaves and heavy stems. This tells us that they have adapted to drier, more open conditions than their thin leaved relatives are used to. It also points out the importance of rapid drainage to prevent rotting of the crown and indicates that ideal planting spots would be on scree-like slopes, between rocks, or in dry walls. However, this does not mean that the roots may ever be permitted to dry out. A constant supply of moisture is still necessary. Fortunately the Auriculas are able to send their long tap-roots deep into cracks and crevices in search of water.

The two groups of Auriculas that can be grown out of doors are the European mountain or alpine Auriculas, and the garden Auriculas. The wild mountain or alpine species and their hybrids are an extensive group. They are by no means impossible to grow, but tricky enough that they do not fall within the limits set for this article. However, as your expertise increases, do try some! They are somewhat difficult to find, but can be obtained from nurseries selling alpine plants. Others can be grown from seed, available through the American Primrose Society and American Rock Garden Society seed lists. A few worth trying are: Primula auricula v. albocincta, P. rubra (also called P. hirsuta), P. x pubescens, and P. marginata.

The garden Auriculas are similar to, but larger than, the alpine Auriculas. Through hybridizing, the color range has been expanded from the original yellow and lavender colors, into odd and interesting shades including brown, mahogany, maroon, crimson, and gray. They usually are found in catalogs simply as Primula auricula. The heavy foliage lasts all season and well into the winter. Their culture is identical to the alpine Auriculas, but they are tougher and easier. Choose a site as described for the mountain species, and plant in a good, gritty soil. Then cover the surface with a thick stone-chip or gravel mulch and partially shade the plants with large rocks if natural shade is absent. They can be divided after flowering just like the other primroses, but often the roots are scanty and it is wise to treat such divisions as cuttings until more roots develop. A special cutting bed with a plastic-covered frame is useful for this. Place it in a bright, but shaded area and take care that it is not too moist or the crowns will rot. Just barely moist at the roots and humid around the foliage is the key to success.

Appearing just a little later than the vernal primroses, but very similar in their cultural needs are the Japanese woodland primroses, members of the Cortusoides section. The one most commonly grown is Primula sieboldii. This is a relatively easy and long lasting primrose, which grows into clumps of scalloped oval leaves. Its underground rhizomes creep over the lightly shaded forest floor, forming three-inch high mats. The umbels of large one to two-inch flowers rise well above the foliage. The species color is magenta-rose. However, pinks, reds, and a pure white are available, all with notched petals, some deeply cut, lacey and frilled-truly beautiful. After flowering, the foliage dies and disappears. The rhizomes can then be easily lifted and divided-but need not be so often as other primroses. Because of this early dormancy and late spring appearance, it is a good idea to carefully mark the patches so you won’t forget where they are and inadvertently dig into them!

Another lovely Cortusoid primrose is Primula kisoana. It has tuffets of geranium-like leaves covered with white fuzz, surmounted by three to five rose colored blossoms. The leaves are not completely expanded until after flowering. It spreads by underground stolons - new baby plants appearing as much as a foot away from the parent-rather like the strawberry begonia (Saxifraga sarmentosa). When a good root system has formed on the offsets, they can be severed and transplanted into well-prepared soil. If the situation is to its liking, this primrose becomes a veritable ground cover. It can also be grown in the rock garden if partially shaded and well mulched with rock chips.

The last primroses to be considered here are the Candelabras. The members of this group are moisture lovers and thrive at bog’s edge and pond-side. Primula japonica is the typical candelabra primrose and the one most often grown. It is quite tall and large leaved, commonly attaining a height of two feet. It will carry as many as six tiers of blossoms, the first tier opening close to the newly expanding leaves. As the stem elongates, succeeding whorls of bloom open for about three weeks, illuminating the transition of spring into summer. When fully open, the leafy clump is as much as a foot across, the foliage long and toothed. P. japonica prefers shade, but with adequate moisture at the roots will tolerate a sunnier spot, even the perennial border. The colors range from wine, through rose and pink, to white. As with P. denticulata, they come easily from seed and self-sow freely. By culling the poorly-colored seedlings, one can obtain quantities of good color selections with little initial outlay. Some of the excellent named varieties obtainable as plants are ‘Glowing Embers’, ‘Miller’s Crimson’, ‘Alba’, ‘Pink Lady’, and ‘Rosea’. Because they are so prolific it is easy, when one has space, to have them in great drifts. When grown this way they truly light up the pond, stream-side or woods that is their home.

Candelabras go completely dormant in fall, retaining no leaves to mark their location through the winter, and since they resume growth very late in spring, one must be careful to mark or remember their location-and not despair of their reappearance.
Having been captivated by primroses, and wanting to try a large variety not easily obtainable, growing them from seed is the next logical step. Here is a simple method that works. Gather together in your work area the following materials: a very fine sterile planting medium such as Jiffy Mix, mixed 3:1 with sharp builder’s sand; coarse grit or fine gravel; some paper towel cut to fit the bottom of your pots; labels and containers (I prefer square two and one-half or three-inch plastic pots). Place a small square of paper towel in the bottom of the pot to prevent washing of the medium through the drainage hole. By the time the towel deteriorates, the medium will have consolidated and will stay put. Fill the pot to the brim with the planting mixture and firm it gently but thoroughly with the bottom of a second pot to about one half inch below the pot rim. Add more medium if necessary. Until now your seed should have been in the refrigerator, secure in a jar with a tight lid. From the envelope, or a folded paper, tap the seed gently onto the surface of the medium-not too thickly. Try to keep them well spaced (about one-eighth to one quarter inch apart). Now cover the entire surface with a thin one-eighth inch layer of the coarse grit or fine stone chips. Label with the plant name, date, and any other pertinent information. Water from below until the surface of the medium is obviously moist. If the medium sinks drastically into the pot you didn’t firm it enough. Place pots securely in a well-drained flat and place the flat in a spot outside where it can remain all winter. Cover flats with an old window screen to break the force of rain and exclude marauding mice and birds. Winter rain and snow should take care of your watering problems, but watch the weather and check if necessary.

Start looking for seedlings when the temperature has been at fifty degrees for a couple of weeks. When they appear, place flats in bright shade, keep moist but not soggy, and continue protection with screen. Seedlings are ready to transplant as soon as they are large enough to handle (usually when first true leaves have appeared). A planting medium consisting of fifty per cent Jiffy-Mix, twenty five percent sand, and twenty five percent garden loam (or a comparable mixture) should be used at this stage. The loam simplifies feeding as it helps retain the fertilizer in the mix, thus reducing the need for frequent feeding.

Using two and one-half inch pots, or flats, fill with the above mix. Again use paper towel squares in the pots, or a sheet of newspaper in flats to hold the medium in. Prick out seedlings and set to just below the first set of leaves, one per pot and one to two inches apart in flats. Water from below and place beneath screens in the shade until established, at which time screens can be removed. Keep well watered and fertilize with soluble fertilizer at least once during the summer. Plant out in prepared area at least one month before expected frost to allow plenty of root development before winter. This will help prevent heaving. A light mulch of evergreen boughs after the ground has frozen also helps. Auriculas may not be large enough to plant out the first year and should spend the first winter in a cold frame or in an area protected from excessive moisture.

I would like to end with a quick reprise on primrose culture. In general, I hope I have convinced you that primroses are easy to grow if their basic requirements are met. All like rich soil, good drainage, plenty of moisture and some degree of shade. They should be divided every second or third year, with the exceptions noted, and replanted in well prepared soil containing plenty of peat or leaf mold, bone meal, wood ashes, and in the case of the denticulata, auricula and farinosa, plenty of fine stone chips or coarse gravel.

So you see-getting involved with a few pretty primroses can open up a whole new world of gardening. To quote Doretta Klaber, that marvelous grower and writer: “Beware! I warn you! Primroses cast a spell. The only way to avoid it is to have nothing to do with the plants. Once you start to grow primroses you are lost. You want more and more, earlier and later kinds, more varieties, more species, more colors. You start with a few plants. You are entranced. Soon your little patch spreads. You divide your plants because you want pools of one color. You raise primroses from seed to have them by the hundreds. A corner at the edge of the woods soon becomes a Primrose Path. The path grows, new paths branch off. Primroses are insidious, they are devastating-growing them becomes a habit. And few things can possibly give you so much pleasure in both anticipation and fulfillment.”

Bibliography
Primroses and Spring by Doretta Klaber. M. Barrows and Co., Inc., New York.
Rock Gardening by H. Lincoln Foster. Bonanza Books, New York.
Pictorial Dictionary of the Cultivated Species of the Genus Primula Ed. by Mrs. J. W. Watson. 1. S. Kohaly Press, Richmond, B.C. Canada.
New Illustrated Encyclopedia of Gardening Ed. by T. H. Everett. Greystone Press, New York.

Wyman’s Gardening Encyclopedia by Donald Wyman. Macmillan Co., New York.
Dictionary of Gardening of the Royal Horticultural Society Ed. by Fred J. Chittenden. Oxford Clarendon Press, Oxford.

Growing Woodland Plants by Clarence and Eleanor Birdseye. Dover Publications, N.Y.
Perennials Time-Life Encyclopedia of Gardening by James Underwood Crocket.
All About Rock Gardens and Plants Walter A. Kolaga. Avenel Books, New York.
All About the Perennial Garden Montague Free. Doubleday and Co., N.Y.

Photo Credit: Ed Buyarski photo of Caroline Jensen's garden at Pearl Harbor in Juneau