Heathers for Warm Gardens

Careful trial of the great many available is making possible the use of many heathers previously thought unsuitable for gardens in warm climates. The author is Professor of Biology at Pacific Union College and Vice President of the Pacific Northwest Heather Society.*

Few people consider California a good place to grow hardy heathers. Cool, moist climates like those of Scotland and England are usually thought of in connection with them. Gardeners in the Pacific Northwest, especially in the Puget Sound area, have been growing heathers for a long time with great success. However, there are a few die-hards who persist in growing heathers in California, in spite of discouraging advice from their gardening friends. Their success has been due in part to proper site selection and soil preparation, but more to selecting heathers suited to warm conditions. One that has been grown for a long time in California is known in much of the literature as Erica mediterranea and, as the name implies, it is native to the Mediterranean region, more particularly to Spain and Portugal. In recent literature it is listed as Erica erigena, and its cultivars are sold as tree heaths. Much of California has a Mediterranean climate with generally mild, damp winters and long, hot, dry summers. It is not surprising, therefore, that tree heaths do well here.

There are other tree heaths, not as well known to Californians, which deserve trial in our climate, namely Erica arborea from the Mediterranean area and North Africa, Erica australis from Spain and Portugal, Erica lusitanica from Spain, Portugal and southwestern France, and Erica terminalis from Corsica, Sardinia, southern Spain, and Italy. Tree heaths are fine-textured, vertically branching, evergreen shrubs from three to ten feet tall. They have limited use in California landscapes, but should not be overlooked. They flower from midwinter to spring and also in summer. The small bell-shaped flowers with colors ranging from white to pink and purple are grouped in terminal clusters that, together, cover the plant. These heaths can be a pleasant addition to a landscape dominated by junipers and other evergreens. Some tree heaths are rapid in growth, reaching a height of three feet or more in three years. Winter hardiness is not a common characteristic of Mediterranean plants and therefore tree heaths may be damaged by sudden frost.

Erica herbacea (E. carnea) ‘Ruby Glow’, a popular winter flowering heather.

Erica herbacea (E. carnea) ‘Ruby Glow’, a popular winter flowering heather. Photographs by the author except where noted.

Nursery catalogs frequently picture a heather with snow on the flowers. This is usually the winter heath, Erica herbacea (E. carnea), native to the Alps, the Apennines and some mountains of eastern Europe and, as would be expected, its fifty or more cultivars are well adapted to cold winters. They are spreading, ground covering plants with abundant small flowers of pure white, pink, red or purple that are beautiful throughout the winter and early spring. However, they do not always prosper in our long, hot, dry summers.

The best qualities of the winter heath and the Mediterranean tree heath are, fortunately, combined in a plant that thrives in California. More than sixty years ago there appeared in the nursery of James Smith and Sons of Derbyshire, England, a cross between Erica herbacea and Erica erigena that has the cold hardiness of the winter heath and the sun tolerance of tree heaths. Its growth is intermediate between ground cover and upright shrub and its flowering habit is close to that of the winter heath. This hybrid is Erica x darleyensis, and one of the oldest selected cultivars of it, called ‘Darley Dale’, has been used in gardens here for a long time. It performs best in full sunlight and can be used either as specimen plant or ground cover. It is somewhat drought tolerant, but thrives best under the same moisture conditions as azaleas. I have seen Erica x darleyensis ‘Darley Dale’ with half opened buds completely encased in ice during a winter storm, but after thawing the flowers opened as if nothing had happened.

Erica x darleyensis ‘Darley Dale’ on the campus at Pacific Union College, Angwin, California.

Erica x darleyensis ‘Darley Dale’ on the campus at Pacific Union College, Angwin, California.

Will other cultivars of Erica x darleyensis thrive as well here? Answers to this and other questions are being found by trial plantings made by members of the Pacific Northwest Heather Society who live in California. One of the most extensive trial plantings is on the campus of Pacific Union College at Angwin, Napa County. It was started in 1979 as a research project in the College’s Department of Agriculture. Plants of seventy heather cultivars were obtained from the University of British Columbia Arboretum. Other gifts and purchases from nurseries here and in England bring the total number of cultivars on trial to 150. Heather Society members are also exchanging plants in an attempt to discover which do best in various parts of California. These are long term projects which will continue to produce information over a period of years as the plants mature and are sub­jected to seasonal and yearly variations in climate. However, some significant facts are already coming from the trial plantings which could help gardeners in selecting heathers for their own gardens.

For instance, all cultivars of Erica x darleyensis, including ‘Darley Dale’, ‘Furzey’, ‘George Rendall’, ‘Silberschmelze’ and ‘Arthur Johnson’ appear to perform best in full sunlight. In shade they made loose wiry growth with very few flowers. In full sunlight or at least six hours of unfiltered sun, they grow into compact mats or mounds up to two feet deep with abundant winter flowers. They spread by tip layering but may be easily kept in bounds by trimming.

A few cultivars of Erica herbacea have already proven themselves in our trial plantings. E. herbacea ‘Springwood White’ is one of the few heathers that flower in dense shade. It is one of the quickest growing ground covers in our plantings. Several plants have spread as much as twelve inches in one year. It does well cascading over a low wall or spreading over a rocky slope. In full sun it spreads more slowly and is low growing — only about four inches high. In shade it forms a looser mat up to eight inches high. It is almost covered with pure white flowers in early spring. This plant is one of the most highly rated in its class by both British and American growers and we are pleased to see it perform well here in north-central California. According to Chapple the plant was found growing wild on Monte Carreggio, Italy, by Mrs Walker of Stirling, Scotland. It was first grown in her garden and introduced in the nursery trade in 1930. I highly recommend it to California gardeners. It will be interesting to learn of habitats in which it performs well. Similar is ‘Springwood Pink’, but we have not grown it long enough to know how it will perform. It appears that Erica herbacea is the most satisfactory heather for low growing ground cover in our area and we have twenty cultivars of this species in our trials.

The genus Erica includes many other species which should be tried in California. We have included in our trials a number of cultivars of Erica cinerea because of the brilliant flowers carried from May through September, but their pattern of growth raises questions about their garden value. New growth is initiated by a few warm days in January and continues vigorously throughout the rest of the winter and spring. Some of our plants appear never to have stopped growing throughout the year except during hot dry weather in August and September. Most cultivars are upright with many stems from the central portion, and this continuous and rapid growth produces plants resembling empty baskets with rings of flowers at the rim. In colder climates these ericas form large mounds rather than empty baskets and remain dormant throughout the winter months, bursting into flower in spring. Their colors are intense, ranging from white to very dark purple. We have not eliminated them from the trial, but we are disappointed in their performance here as compared with other climates. We are pruning several of them severely in an attempt to slow them down.

Erica tetralix has not yet made a good showing in our plantings. However, its gray-green foliage and large bell-like flowers set it apart from most other heathers, and it may have value for the contrast it provides. It appears to be quite tolerant of high temperatures and bright sunlight.

Erica vagans has some outstanding cultivars that may be adaptable to California gardens. E. vagans ‘Mrs D.F. Maxwell’ is widely grown. The foliage is dense and compact, which gives it good form as a specimen plant. The bright pink flowers open from July through September forming dense upright racemes up to six inches long. The plant may be as high as eighteen inches in full sunlight. Plants in the shade do not flower well.

Erica ciliaris and some of its cultivars are performing nicely in the trials. The flowers are some of the largest (up to half an inch long) on any of the ericas that are winter hardy here. The foliage is fine textured but the plants are rather loose and shapeless. They will look better in mass plantings than as specimen plants.

Gardeners in parts of California where the temperature never drops below 28° F. and frost is infrequent can include the fascinating Cape heaths in their plantings. There are nearly five hundred species within the genus Erica, and most are from South Africa. Manning’s Heather Farm in Sebastopol, Sonoma County, near the northern California coast specializes in this group of heathers and they have many from which to choose. Those of us in more severe climates can only look longingly at these colorful heathers, or maybe grow them in containers so they can be moved indoors during frosty weather. Some are borderline cases and may thrive for several mild winters only to be cut down during a severe freeze. Erica mollis and E. canaliculata (still sold incorrectly as E. melanthera) are examples of borderline plants in our trial plantings. Against a south wall we have a four year old plant of Erica mollis that was a solid mass of light lavender flowers during November, December and January of the past two mild winters. One night below 26° F. will reduce it to a mere entry in our records. It is grown for cut flowers in milder parts of California and is sometimes referred to as the regerminans heather.

The true Scotch heather or ling, Calluna vulgaris, is distinctly different from the ericas. It is an extremely variable species with a fascinating array of cultivars — over 300 of them in the nursery trade. This diversity has led us to search for those that show adaptation to our climate. Of the fifty named cultivars in the Pacific Union College heather trials, there are a few that appear to be well adapted to this north-central California climate. In fact, there are some that are little known in the nursery trade that seem to be better than those being sold.

Calluna vulgaris ‘Sister Anne’ has done particularly well here in an exposed, rock garden setting. The common Scotch heather of the moorlands is an upright shrub with wiry branches. C. vulgaris ‘Sister Anne’, however, crawls over the ground as a soft-textured, mossy carpet. It was discovered by Anne Moseley growing in crevices of serpentine rock near the Lizard in Cornwall, England. The fact that many northern California soils are serpentine may have something to do with the success of this plant here. I was concerned at first to know how it would respond to our intense summer heat, but it appears to be somewhat drought resistant. The coastal cliffs of southwestern England are open to winds that sometimes leave the thin layer of soil dry, and the low growing mat-like form of this plant is typical of those stressed by desiccating winds. Plants in our trials are spreading by tip layering, and have begun to cover an adjacent rock which, no doubt, gets rather hot in the summer. There are other heathers similar to C. vulgaris ‘Sister Anne’. One of these is C. vulgaris ‘Dainty Bess’ which, according to Van de Laar, originated in the United States in 1962. We have not had success with ‘Dainty Bess’ or its relative ‘Bess Jr’, but they should be tried elsewhere.

Two other heathers originating in the United States are of interest in our trials. Calluna vulgaris ‘Californian Midge’ was apparently discovered as a seedling in a garden in California and sent to Fred J. Chapple, an English heather grower, who propagated it and sold it under its present name. It is a lovely rock garden plant forming a neat mound of compact bright green foliage up to ten inches in diameter. The British Heather Society gives it good marks in their heather trials and I believe it will do as well for us. I purchased C. vulgaris ‘Valorian’ from Mayfair Nurseries in Pennsylvania about 1973. According to Walter Kolaga, owner of the nursery at that time, it resulted from a cross between C. vulgaris ‘Mrs Ronald Gray’ and C. vulgaris ‘Foxii Nana’. In our trials it is a slow growing mat of rich dark green, the tips of new growth marked with a lighter green. I believe it has a definite place in California gardens.

It is interesting to note that most cultivars of Calluna vulgaris have been chance seedlings found in nurseries and heather gardens or among plants in the wild. Very little controlled crossing and selection has been done. There are so many cultivars already available that it is more important to try them out in a variety of conditions than to produce new ones. However, a plant as variable as this may provide hybrids for many different habitats if deliberately bred.

An interesting example of a Calluna vulgaris cultivar that was discovered in its native habitat is C. vulgaris ‘Mrs Pat’. According to Fred Chapple it was found by the wife of P.S. Patrick while she was walking with her dog on the moors in the vicinity of Maxwell and Beale’s nursery. She recognized it as something different because of its colorful coral-red tipped foliage so she dug it up with her walkingstick and carried it home. Today it is grown around the world and is performing nicely in our trial plantings when exposed to at least six hours of unfiltered sunlight each day. A plant of ‘Mrs Pat’ growing in my back yard in the shade of large oak trees has shown no color on the new growth except pale yellow.

The double flowers of Calluna vulgaris ‘H.E. Beale’. Staff photograph.

The double flowers of Calluna vulgaris ‘H.E. Beale’. Staff photograph.

Calluna vulgaris ‘H.E. Beale’ is another Scotch heather found by chance. About 1925 a lady whose identity is unknown was walk­ing in the New Forest in southern England and noticed a heather with double flowers. She picked a sprig of it and sent it to the nursery of Maxwell and Beale for identification. The twig had three side shoots about one half inch long and since it was new to them they carefully made cuttings of these and were successful in rooting two of them. From those two cuttings have come all the plants of this widely grown heather and no one else has been able to find the original plant in the New Forest.

Another widely grown double Scotch heather is Calluna vulgaris ‘Tib’, discovered in 1934 on the Pentland Hills near Edin­burgh, Scotland, by Miss Isobel Young. Tib is an affectionate nickname for those called Isobel in Scotland. This cultivar, introduced by Maxwell and Beale in 1938, is the earliest of the double-flowered cultivars to bloom. The origin of the white double Scotch heather Calluna vulgaris ‘Alba Plena’ is disputed. According to Fred Chapple it was discovered in the Black Forest of Germany by an English climber. While taking refuge from a storm he noticed an unusual flower at his feet and collected a portion of the plant on which it grew. John Letts says it originated in Germany, but as a sport of the older cultivar ‘Alba Elegans’. Still another authority, Harry Van De Laar, says that an American seedling ‘Else Frye’, selected in Seattle, is essentially the same as ‘Alba Plena’.

Among the dwarf forms of Calluna vulgaris is ‘White Mite’, a small rounded ball of green that was found above 3000 feet on Sgoran Dubh, in the Cairngorm mountains east of Inverness, Scotland. Another dwarf and compact form called ‘Minima Smith’s Variety’ was propagated from an unusual growth called witches broom that is reproduced vegetatively. Those in our trials develop fascinating shapes — some like fox tails and others like miniature pine trees trained as bonsai.

Calluna vulgaris ‘Robert Chapman’ prized for the color of its foliage

Calluna vulgaris ‘Robert Chapman’ prized for the color of its foliage.

Winter foliage color is an attractive characteristic of a number of Scotch heathers. Calluna vulgaris ‘Orange Queen’ and C. vulgaris ‘Robert Chapman’ turn rich orange-red as soon as temperatures drop below 40° F. in November and retain the color until spring growth begins. C. vulgaris ‘Cuprea’ has coppery tips and C. vulgaris ‘Aurea’ is a mixture of gold, copper and red during the colder part of winter. There are many others with colored foliage in winter, but in all cases sunlight is essential for its development and plants in the shade will be drab. In fact, these plants are best situated in such a way that they will be viewed from the south, because the brightest colors are on the side facing the winter sun.

Heathers are not readily available in California nurseries. The catalogs of the largest do not list heathers at all. A few nurseries list four or five cultivars, mostly incorrectly named. You are more likely to find them in retail stores or specialty nurseries. Most retail nurserymen could get them for you by ordering from growers in Oregon and Washington or the northeastern states. As more people become aware of heathers and of their usefulness in California the demand for plants will encourage more retailers to carry them. Members of the Pacific Northwest Heather Society in California will help by introducing heathers to this climate. Rooted cuttings are being shared among members and everyone who grows them contributes to the larger experiment of determining which are best in California.