Rock garden primulas

Editor’s note: This article by the late Ken Girard was originally published in 1999 in the CRAGS Newsletter, “The Voice of the Calgary Rock and Alpine Garden Society” (www.crags.ca), and republished in that group’s Feb. 2008 newsletter. Ken was also president of the Calgary Horticultural Society. Keep in mind that Calgary is not Upstate New York. According to Wikipedia, “Calgary has a semi-arid, highland continental climate with long, dry, but highly variable, winters and short, moderately warm summers (Koppen climate classification BSk, USDA Plant Hardiness Zone 3b).”

Some of my very first experiences with gardening in the great outdoors were with primulas, known to me then as hardy African violets – at least that’s what I called them. I wasn’t familiar with the proper names of many perennials at eight years old, but I had always admired plants lining the walkway to my piano teacher’s door. She grew African violets inside, so these must have been outside ones. One spring these plants had been, in my estimation, decimated, hardly anything left. I asked what had happened and was told that they had been thinned and the leftovers were behind the fence if I wanted any. Did I and how? So began my love affair with Auricula or Dusty Miller primulas.

Nothing says spring to me like a clump of Primula auricula in full bloom. The foliage is succulent with varying degrees of grey, white, gold or silver farina and the flowers are held above the foliage on stems which are also covered in farina. Flower colour ranges from palest yellow to rich gold; violet purple to mauve, as well as pink, cerise and red. Including novelty colours such as brown, tan and green, there are auriculas for everyone’s taste. Auriculas have been such favourite plants for many years in England that there are whole societies dedicated to them and the hybridization that is taking place is absolutely amazing.

I have found it easiest to grow auriculas in semi-shade to full sun as long as the soil does not bake for extended periods of time. In fact too much shade will weaken a clump of Auricula primulas faster than anything else, followed closely by soggy soil. Most of the plants in my garden grow in areas where the tops are in sun most of the day but the roots are carefully tucked behind rock. The soil is composed of 50% grit, 25% compost and 25% of a manure/loam mix. Many of these primulas will actually grow in Calgary gumbo but do far better in a rock garden mix. They flower more profusely and tend to grow in tighter clumps.

The species that comprise this group of primulas are definitely garden worthy as are many of their hybrids and most of them are hardy for us if given a little winter protection. The earliest plants in this group of primulas to flower for me is Primula marginata, a species with lavender flowers and beautifully serrated leaves. The flowers appear in mid-April and last for a few weeks. The plants themselves are rather small when compared to others of the clan and fit well in troughs and dish gardens as well as smaller rock gardens. The foliage stays fresh for most of the summer but eventually goes yellow and dries off by September, leaving behind the large winter bud which contains next years leaves and flowers. There are many selections of P. marginata worth obtaining and growing as well as it’s many hybrids. One of the most popular hybrids is P. ‘Linda Pope’, a fantastic plant with large lavender flowers held well above the beautifully serrated leaves. Some hybrids lose the intensity of the serration on the leaves.

A species which needs to be more popular is Primula hirsuta. It is a mid-sized plant, grows about four inches across in tight clumps, mid-green in colour with a light farina. The flowers are hot pink to cerise depending on the plant. I purchased Primula hirsuta at a nursery on the west coast, planted it, it survived beautifully and bloomed the next year. It was so spectacular, I promptly went back to that nursery the next spring and purchased five more. Hopefully we will see more of them in the near future.

The main species of the Primula auricula group are medium- to large-growing plants that have beautiful fragrant flowers held above the foliage. The original species have small delicate flowers covered in white farina and come in yellow and purple. Plants can range from four to over eight inches in diameter and grow into rather large clumps. The leaves are succulent and usually covered in either silver or gold farina. With the extensive hybridization and selection that has taken place these primulas can now be had in almost any colour except true black, but there are such dark purple ones out there that from a distance they look black. The flowers can come in several colour patterns: selfs (one colour throughout), goldbands, white-eyed, yellow-eyed, completely covered in farina. The possibilities are endless. There are now double-flowering selections, but I have found these to be less hardy and definitely less vigorous than the single forms. They are definitely for the collector and need a little extra coaxing to do well.

Hybrids between the various species of plants in this group of primulas are popular with gardeners and deservedly so. With hybridization, a wide range of plant sizes, growth habits and flowering seasons and colours has been produced. Primula x pubescens (Primula auricula x P. hirsuta) is a desirable grouping of plants giving rise to many of the best garden cultivars. Primula ‘Beverly White’, P. ‘Rufus’, P. ‘Boothman’s Variety’ are all selections of Primula x pubescens. There are many more out there to be had and tried.

Other primula species that I have grown are P. glaucescens which is a small plant for the trough or crevice garden with lavender-pink flowers in small clusters. Primula belluensis is a bit larger than P. glaucescens and has rose to pink coloured flowers. Both of these species require soil with good drainage to do their best. A very choice species in this group is Primula allionii. A rock gardener's dream! It is a diminutive plant well worth growing. Many people grow it in troughs or pans and everyone says, do not get the leaves wet, especially in winter. Those growing it here say that the trick is to make sure it has perfect drainage; grow it sideways or upside down in a crevice with no direct sun. Because we do not have the same problem with winter wet here as many people on the coast do, this worry may be unfounded. There are hybrids of P. allionii available that are definitely worth trying such as P. x miniera (P. allionii x P. marginata). Hopefully through hybridization the exacting requirements of P. allionii can be alleviated a bit.

By late summer all of these plants are beginning to get ready for winter. This year’s leaves will begin to yellow, eventually drying out. These leaves should be left for winter protection as next year’s leaves and flowers will already be produced in a resting winter bud. Do not let the plants ice over or stay too soggy during the winter, this can lead to stem or root rot which is very unfavourable. Some of the more delicate species and hybrids may need some winter protection from sun and wind so a light covering of straw would be best. A mulch which absorbs moisture and keeps the plants wet can be detrimental to the plants.

Fertilizing is best done in the spring with a surface dusting of bone meal applied around the plants. I try to keep the nitrogen to a minimum as this promotes large lush leaf growth, reduces flowering and may make the plants too soft for wintering properly. Dividing is best done either after flowering or in early fall as the plants Primula x pubescens Windrush are going dormant. I prefer division after flowering but can’t always get to it As the clumps grow the stems become rather unsightly, especially on the larger plants. Clumps are best lifted removing the soil from around the roots and with a sharp knife cut through the plant Try to get a few roots with each piece and replant where you want them setting the plant a bit deeper than it originally was so that the buried stem can root out. Cuttings can also be taken, these are best done in late spring and kept in a cool moist area until rooting has taken place and planted out in the garden in the fall or for really tender or rare plants next spring, wintering in a cold frame.

I have had very few pest problems with primulas but occasionally see aphids on the soft tender growth or flower stalks. Gently removing aphids either by hand or a gentle stream of water usually works during the growing season. Watch for black aphids in and around the winter crowns in late summer and be prepared to use an insecticide to eradicate them. Slugs may feast on the leaves especially in spring so be on the lookout for their tell tale trails and leaf damage.

As you can see there are many species and varieties of rock garden primulas just in this group that are worth trying. All garden centres carry the regular P. auricula type hybrids but you need to go early if you want to select and purchase them in flower. Seed from seed exchanges is another way to obtain these treasures but one needs to be patient when growing primulas from seed, and sometimes the seed can be mislabeled or possibly of hybrid origin. Named varieties and true alpine treasures need to be ordered from specialty nurseries and shared amongst your friends through trading and selling at plant sales; Go ahead try a few, I know you will enjoy these early spring jewels of the alpine garden.