The landscape evaluation of Hebe at the North Willamette Research and Extension Center (NWREC) was established in 2000 and was removed in 2009. The purpose of the planting was to compare performance of a range of Hebe species and cultivars under typical western Oregon conditions and gather information on their landscape performance. One of the main goals of this trial was to develop comparative data on hardiness of Hebe cultivars and species and identify cultivars that were capable of tolerating typical cold events in a Pacific Northwest winter. In addition to assessing hardiness, other goals were to record flowering and growth information on the various cultivars and species, and also any pest or disease problems.
- Data Collection
- Cold Hardiness of Hebe Cultivars and Species
- Cold Hardiness Results
- Pests and Diseases
- Drought Tolerance
- Books and Websites
The first 48 selections of Hebe were planted in 2000. Over the following 4 years, plants were received from cooperators, usually as unrooted cuttings. These were rooted, grown on to 4” or 1 gallon-sized plants, and added to the evaluation each April. In 2001, 88 selections were added to the planting, and in 2002, an additional 45 were added. In 2003, 80 were added, and a final 33 selections were planted in 2004. Primarily because of plant losses to cold and to some extent disease, the evaluation consisted of 201 clones in November, 2006.
The planting consisted of a 0.4-acre plot, with 16 double rows, with individual plants spaced at 3’ by 3’ within each double row. Three plants of each clone were planted to allow statistical evaluation of data, although because of the sequential planting over several years, the plants are not randomly distributed in the evaluation, but planted in groups of three. Planting occurred once per year, in April or May, to allow for good plant establishment before winter. Following planting, each row was mulched with bark dust.
Each established plant was fertilized with 2 tbs of 13-13-13, while each new plant received ½ tbs of the same fertilizer. A 5’ wide grass strip separated each row for access. A micro sprinkler irrigation system was installed with the assistance of a grant from the Hardy Plant Society of Oregon.
Meteorological data, including daily maximum and minimum temperature, rainfall and wind speed, are available from the US Bureau of Reclamation Agrimet weather station installed in 1998, located immediately adjacent to the plot.
Plants came from a variety of sources in the western United States and Canada, including nurseries in Oregon, the University of California (Santa Cruz) Arboretum, Strybing Arboretum in San Francisco, Washington Park Arboretum in Seattle and the University of British Columbia Botanical Garden in Vancouver, B.C. However, the majority of the collection was provided by cooperators the New Zealand and the United Kingdom, including Lincoln Botanical, Landcare Research and Christchurch Botanic Garden (New Zealand) and individuals within The Hebe Society (U.K.).
Plant size was recorded at planting time and again in October at the end of the growing season. Plant size was recorded by measuring the height, and two width measurements at right angles to one another, allowing a plant size index to be calculated.
Data on flowering was collected once per month throughout the year, as flowering on various selections continues almost year-round. Flowering information included a rating of flowers on a 0-5 scale. Cold hardiness information was collected following cold events and again in early April. Plants were rated for damage on a 0-5 scale, with 0 indicating no damage and 5 indicating plant death. Intermediate ratings indicate varying levels of damage to leaves and shoot dieback. Information on insect pests and disease problems was collected on a casual basis. The main disease problems proved to be Phytophthora root rot; leaf spot, caused by Septoria exotica, and downy mildew, caused by Peronospora grisea. See Pests and Diseases for more information. A more recent evaluation involves assessing foliage quality and form of the plants, again on a 0-5 scale. The goal was to give some indication of the appearance of the plant in general.
Cold hardiness of Hebe cultivars and species
In New Zealand, Hebe species can be found growing in a wide range of habitats, from sea level to alpine regions, so it is no surprise that cold hardiness of the species, and the cultivars derived from them, varies widely as well. There is truth to the old saying that hardiness of Hebe is related to leaf size. As one goes up in elevation from sea level to alpine areas in New Zealand, the leaf size of the Hebes tends to decrease, and overall plant size decreases as well (Kristensen, 1989). Other characteristics like coriaceous and/or glacous leaves and white flowers are also typical of alpine Hebe species (Wardle, 1978). So, generally speaking, you could say that the larger the leaf of the Hebe, the less cold hardy it tends to be. As with all living things, the rule is not perfect, but the most tender Hebes are usually the largest-leaved, and the hardiest are those with the smallest leaves.
The most extensive study of cold hardiness of Hebe was undertaken by Warrington and Southward (1995), who assessed summer and winter hardiness of 35 species and cultivars. This study showed that large differences in hardiness existed among the various selections. Not surprisingly, the hardiest of those tested were two whipcords, H. cupressoides and H. propinqua, both of which are typically found in alpine or subalpine regions and have very tiny leaves. More important than altitude however, this study observed significant differences in hardiness of species from northern or southern parts of New Zealand, with species of southern origin exhibiting greater overall hardiness.
Some of the research on hardiness of Hebe has utilized excised shoots as sample material for laboratory studies. Bannister (1986) found that detached shoots of Hebe albicans, a South Island species often found in subalpine scrub above 1000m, withstood mid-winter temperatures of -10°C, one of the hardier of the native species studied. Other Hebe species were not tested. In a more extensive study, Bannister (1990) found that mid-winter freezing resistance of foliage of H. buchananii, a diminutive shrub of alpine areas in Canterbury, was as low as -11°C. Freezing resistance of foliage of H. rakaiensis and H. salicifolia, both of which are found at lower elevations on the South Island, was found to be -5.2°C and -6°C respectively. Buds of H. rakaiensis were found to be hardy to -11°C, significantly hardier than leaves. Testing of both H. speciosa, a tender species from seacoast areas of the North Island, and H. odora, a widely distributed shrub of subalpine scrub, found early-winter hardiness of -6°C and -9°C, respectively. Sakai and Wardle (1978) tested excised stems of a wide variety of New Zealand trees and shrubs in mid-winter for hardiness. H. brachysiphon was rated as one of the hardiest species tested, having leaf and bud hardiness of -10°C and -13°C, respectively.
Probably the most extensive anecdotal evidence for hardiness of a wide range of Hebe species and cultivars is provided by Trees and Shrubs hardy in the British Isles (Bean and Clarke, 1991). This monumental work, in 5 volumes, lists descriptions and basic hardiness information on over 100 Hebe species and cultivars. The most extensive field trial of Hebes which included cold hardiness results was the trial of RHS Garden Wisley between 1980 and 1982. In addition to selecting 33 cultivars or species for awards, the trial also indicated which of the trialed plants failed to survive the winter of 1981. Harris and Decourtye (1995) evaluated cold hardiness of many New Zealand plants in field trials over several years in Angers, France. This trial indicated that H. dieffenbachii was tolerant of prolonged cold weather with temperatures as low as -12°C. H. pauciramosa, H. pinguifolia and H. amplexicaulis showed some foliar damage from these conditions. Later data from this trial (Harris et al. 2000) showed that H. albicans and H. subalpina were not injured or suffered only slight injury from prolonged winter cold snaps with temperatures as low as -15°C.
In North America, Hebes are grown primarily as a landscape plant. Because of the intolerance of most Hebes for excessively hot or cold weather, cultivation of Hebes in North America is almost entirely limited to west of the Cascade or Sierra Nevada Mountains in California and the Pacific Northwest. Elsewhere in North America, the climate is generally too cold or hot, or both, to allow for outdoor cultivation, although dedicated enthusiasts have been successful with some varieties in many other areas.
Even in the Pacific Northwest, Hebes are sometimes thought of as too tender for general landscape use, a reputation which is primarily the result of experience with a few popular cultivars which are not particularly cold hardy. Plantings of ‘Amy’, ‘Tricolor’ or ‘Patty’s Purple’ have been severely damaged in cold events on a regular basis, which has unfortunately given the entire genus this reputation. The key to growing these tender cultivars is to provide a protected location near a house or nearby plant.
Despite this, many other commonly-available Hebe cultivars like ‘Emerald Gem’, H. carnosula, or H. cupressoides ‘Boughton Dome’, never suffer winter damage.
The level of injury to cold will of course vary depending on the temperature experienced. The hardiest Hebes-the whipcord types and other small-leaved plants-have not typically shown any reaction to winter temperatures in western Oregon over the course of this trial. Since 2000, the minimum temperatures have been no lower than 19°F (-7°C). Even tender Hebes will tolerate temperatures of 25°F without showing signs of stress, especially if these temperatures occur in mid-winter. Abnormally cold temperatures in the fall or early spring are often responsible for damage to these plants and that has been the case in this trial.
The mildest form of damage is leaf discoloration at the shoot tips. More severe cold damage will cause browning and leaf loss on shoot tips.
Major cold damage will cause browning of most of the leaves on the canopy, followed by dieback. Sometimes, plants will recover over a 2-3 year period from this damage if subsequent winters are mild. Very severe, sudden cold often turns the entire plant brown and sensitive cultivars do not recover from this damage and require replacement.
Bannister, P. 1986. Winter frost resistance of leaves of some plants growing in Dunedin, New Zealand, in winter 1985. New Zealand Journal of Botany. 24:505-507.
Bannister, P. 1990. Frost resistance of leaves of some plants growing in Dunedin, New Zealand, in winter 1987 and late autumn 1989. New Zealand Journal of Botany. 28:359-362.
Bean, W.J. and D.L. Clarke. 1991. Trees and shrubs hardy in the British Isles. 5 Volumes. John Murray.
Harris, W., A. Cadic and L. DeCourtye. 2000. The acclimatization and selection of New Zealand plants for ornamental use in Europe. Proceedings of the 19th International Symposium on Improvement of Ornamental Plants. Acta Horticulturae 508:191-196.
Harris, W. and L. Decourtye. 1995. Observations on cold damage to New Zealand plants grown at Angers, France. Horticulture in New Zealand. 6(1):9-19.
Kristensen, L. 1989. The Genus Hebe-A botanical report. Danish research Service for Plant and Soil Science. Report #S-2034.
Sakai, A. and P. Wardle. 1978. Freezing resistance of New Zealand trees and shrubs. New Zealand Journal of Ecology. 1:51-61.
Wardle, P. 1978. Origin of the New Zealand mountain flora, with special reference to trans-Tasman relationships. New Zealand Journal of Botany. 16:535-550.
Warrington, L.J. and R.C. Southward. 1995. Seasonal frost tolerance of Hebe species and cultivars. New Zealand Journal of Crop and Horticultural Science. 23:437-445.
Cold Hardiness results
Winter temperatures over the course of the trial varied significantly, as might be expected. Temperature data for each period from late October through mid-March, from 2000-2006, are shown in the graphs below. Generally speaking, only temperatures of 27°F or below are of significance, as in this trial, even the most tender Hebe seemed not to suffer injury above this temperature, regardless of when it occurred. More than the actual minimum temperature, the date on which a low temperature was recorded has had the most profound impact on Hebe survival and damage at this site.
The most serious cold damage which occurred during the evaluation followed cold temperatures in early November, 2002, when temperatures dropped suddenly to 22°F. This was a particularly early freeze that caught many Hebes growing and in full bloom, and did extensive damage to many selections, some of which failed to recover. A similar, though less severe freeze, occurred on November 1, 2003, when the temperature again dropped quickly from mild lows to 24.6°F. Again, because of the relatively severe temperature early in the winter, significant damage was done to a wide range of plants. Another early freeze occurred in the first winter of the trial, when the temperature dropped to 23°F on November 18th. The fourth severe freezing event occurred in mid-February, 2006, when the temperature dropped to 20°F on February 20. Much like the early November freezes, this was an uncharacteristically low temperature for the time of year, and occurred following a period of relatively mild temperatures. By late February, many plants, including Hebes, are beginning to grow, and are more susceptible to cold injury. These four events accounted for virtually all of the observable damage to Hebes over the duration of this trial.
In contrast to the injury caused by these early, or late, freezes, similar temperatures in mid-winter have caused no identifiable damage. Temperatures in the low 20’s°F have occurred in January 2004 (20°F, January 6), January 2005 (23°F, January 5) and December 2005 (19.5°F, December 16). In two of the winters of this evaluation (2001-02 and 2004-05), winter temperatures were so mild that no damage which could be attributed to cold weather could be observed.
The accompanying chart shows cold damage to Hebes in the trial by year.
|Cold damage rating by year|
|1B||13||2000||H. sp. (bidwillii)='Pattys Purple'||4.0||.||4.3||.||.||.||4.2|
|1B||16||2000||H. sp ('Little')||2.0||.||4.0||.||.||.||3.0|
|2A||1||2000||H. sp ('Powis Castle Blue')='Blue Mist'||0.0||.||.||.||.||.||0.0|
|2A||7||2000||H. anomala 'Purpurea'||0.0||.||0.0||0.0||.||1.3||0.3|
|2A||19||2000||H. sp (buxifolia)||0.0||.||0.0||.||.||.||0.0|
|2B||1||2000||H. sp (NWREC 528)||0.0||.||0.0||0.0||.||1.0||0.3|
|2B||13||2000||H. cupressoides 'Boughton Dome'||0.0||.||0.0||0.0||.||0.0||0.0|
|2B||16||2000||H. 'Silver Queen'||3.6||.||5.0||.||.||.||4.3|
|3A||1||2000||Heliohebe 'Hagley Park'||0.0||.||2.6||0.0||.||0.0||0.7|
|3A||4||2000||H. sp ('Prince')||3.0||.||5.0||5.0||.||.||4.3|
|3A||7||2000||H. sp. (haastii)||0.0||.||0.0||0.0||.||.||0.0|
|3A||13||2000||H. pinguifolia 'Pagei'||0.0||.||2.0||0.0||.||0.0||0.5|
|3A||25||2000||H. speciosa 'Tricolor'||5.0||.||.||.||.||.||5.0|
|3A||28||2000||H. sp. ('Cottage Red Edge')||2.0||.||.||.||.||.||2.0|
|3B||10||2000||H. 'Silver Queen'||2.6||.||4.6||.||.||.||3.6|
|3B||25||2000||H. speciosa 'Variegata'||2.3||.||5.0||.||.||.||3.7|
|3B||31||2001||H. x andersonii 'Andersonii Variegata'||.||5.0||.||.||.||5.0|
|4A||10||2001||La Seduisante' 83.113||.||5.0||.||.||.||5.0|
|4A||13||2001||H. speciosa 91.612||.||4.0||3.0||.||2.0||3.0|
|4A||16||2001||H. corriganii 91.663||.||1.3||1.0||.||1.0||1.1|
|4B||1||2001||H. odora 'New Zealand Gold'||.||0.0||0.0||.||0.0||0.0|
|4B||13||2001||Parahebe 'Snowcap' 94.96||.||2.0||3.6||.||.||2.8|
|5A||1||2001||H. stricta var. macroura||.||4.0||3.5||.||1.0||2.8|
|5A||7||2001||H. sp. (Strybing H-2)||.||0.0||0.0||.||0.0||0.0|
|5A||16||2001||H. albicans 'Snow Cover'||.||1.0||1.3||.||0.0||0.8|
|5A||22||2001||Purple Tips' 89.54||.||5.0||.||.||.||5.0|
|5A||25||2001||H. albicans (prostrate form)||.||2.0||2.0||.||0.0||1.3|
|5A||31||2001||H. sp (Strybing H-12)='Autumn Glory'||.||4.0||2.0||.||0.0||2.0|
|5B||1||2001||H. sp (Strybing H-8)='Andersonii Variegata'||.||5.0||.||.||.||5.0|
|5B||4||2001||H. macrocarpa var. brevifolia||.||5.0||.||.||.||5.0|
|5B||19||2001||Andersonii Variegata' 83.118||.||5.0||.||.||.||5.0|
|5B||25||2001||H. traversii 89.5||.||5.0||.||.||.||5.0|
|5B||28||2001||H. stricta var. lata||.||3.0||2.0||.||0.0||1.7|
|5B||31||2001||H. sp. (Strybing H-1)||.||5.0||.||.||.||5.0|
|6A||4||2001||H. macrocarpa v. brevifolia 84.78||.||.||0.0||.||0.0||0.0|
|6A||7||2001||H. sp. (Strybing H-14)||.||1.0||0.0||.||0.0||0.3|
|6A||10||2001||H. albicans 'Sussex Carpet'||.||2.0||1.3||.||0.0||1.1|
|6A||16||2001||H. sp. (Strybing H-16)=H. rigidula||.||2.0||1.3||.||0.0||1.1|
|6A||19||2001||H. diosmifolia (Strybing H-15)||.||3.0||0.0||.||0.3||1.1|
|6A||22||2001||H. sp (Strybing H-10)||.||5.0||.||.||.||5.0|
|6A||25||2001||H. sp. (Strybing H-9)||.||4.6||3.0||.||2.0||3.2|
|6A||28||2001||H. salicifolia v. angustissima||.||3.0||3.3||.||1.6||2.6|
|6B||1||2001||H. parviflora var. angustifolia||.||2.6||1.3||.||2.0||2.0|
|6B||4||2001||Pink Payne' 88.102||.||4.6||.||.||.||4.6|
|6B||13||2001||H. macrantha 91.631||.||0.0||0.0||.||0.0||0.0|
|6B||28||2001||H. elliptica 'Variegata' (Strybing H-13)||.||5.0||.||.||.||5.0|
|6B||31||2001||H. diosmifolia 84.75||.||5.0||.||.||.||5.0|
|7A||1||2001||H. sp. (Western Hills)||.||0.3||0.0||.||0.0||0.1|
|7A||4||2001||Wiri Gem' 94.56||.||5.0||.||.||.||5.0|
|7A||7||2001||H. sp. (elliptica x crassifolia)||.||.||0.0||.||0.0||0.0|
|7A||13||2001||H. sp. (Strybing H-3)||.||0.0||0.0||.||0.0||0.0|
|7A||16||2001||Mohawk' (=Purple Pixie)||.||4.0||2.3||.||0.0||2.1|
|7A||22||2001||H. sp. (Strybing H-4)||.||5.0||.||.||.||5.0|
|7A||25||2001||H. x lewisii 'Lewisii'||.||5.0||.||.||.||5.0|
|7B||1||2001||H. macrocarpa var. latisepala||.||5.0||.||.||.||5.0|
|7B||28||2001||H. sp. (Strybing H-5)||.||4.0||.||.||.||4.0|
|8A||1||2001||H. brachysiphon 89.218||.||5.0||0.0||.||0.0||1.7|
|8A||4||2001||H. macrocarpa var. macrocarpa||.||0.0||.||.||.||0.0|
|8A||10||2001||H. pimelioides 'Quicksilver'||.||0.3||0.0||.||0.0||0.1|
|8A||13||2001||H. albicans 242/99||.||1.0||1.5||.||0.0||0.8|
|8B||1||2001||H. speciosa 'Pink'||.||5.0||.||.||.||5.0|
|8B||4||2001||H. hectorii var. laingii 94.53||.||0.0||0.0||.||0.0||0.0|
|8B||10||2001||H. sp. (Halifax Hardy)||.||0.0||0.0||.||0.0||0.0|
|8B||13||2001||H. subalpina 331-98||.||0.4||1.0||.||0.0||0.5|
|8B||32||2001||(do not record, mix of clones)||.||.||0.0||0.0||0.0|
|9A||1||2001||H. macrocarpa 'Pink'||.||5.0||.||.||.||5.0|
|9A||7||2001||H. sp. (diosmifolia x albicans)||.||2.3||3.0||.||0.0||1.8|
|9A||19||2002||H. 'Affinis' 89.60||.||5.0||.||.||.||5.0|
|9A||22||2002||Pink Paradise (PVR)||.||1.0||2.0||.||2.0||1.7|
|9A||25||2002||H. sp. 84.86||.||5.0||.||.||.||5.0|
|9A||28||2002||H. gibbsii 89.44||.||0.0||0.0||.||0.0||0.0|
|9A||31||2002||H. sp. (odora var. prostrata)||.||0.0||0.0||.||0.0||0.0|
|9B||4||2001||H. albicans 83.120||.||1.0||1.3||.||0.0||0.8|
|9B||10||2001||H. carnosula 'Mount Stewart'||.||0.0||0.0||.||0.0||0.0|
|9B||19||2002||H. sp. (Strybing H-17)||.||3.0||3.5||.||0.0||2.2|
|9B||22||2002||H. sp. (venustula)||.||1.0||3.6||.||0.0||1.5|
|9B||28||2002||Wiri Spears' 94.61||.||4.3||.||.||.||4.3|
|9B||31||2002||H. townsonii 91.747||.||4.6||.||.||.||4.6|
|10A||1||2002||Parahebe formosa 90.178||.||2.0||3.0||.||4.0||3.0|
|10A||4||2002||H. albicans 83.120||.||0.6||0.0||.||0.0||0.2|
|10A||7||2002||H. divaricata 84.76||.||3.0||0.0||.||0.0||1.0|
|10A||10||2002||H. venustula 'Sky Blue'||.||0.3||0.0||.||0.0||0.1|
|10A||13||2002||H. cupressoides 'Nana' 89.23||.||0.0||0.0||.||0.0||0.0|
|10A||16||2002||H. sp. ('Patty's Purple Variegated')||.||5.0||.||.||.||5.0|
|10A||19||2002||H. ochracea 'James Stirling'||.||0.0||0.0||.||0.0||0.0|
|10A||22||2002||Clear Skies' PVR||.||1.0||0.0||.||.||0.5|
|10B||1||2002||H. pauciramosa var. masonae||.||0.0||0.0||.||0.0||0.0|
|10B||7||2002||H. sp. (pinguifolia)||.||0.0||.||.||.||0.0|
|10B||10||2002||H. salicornioides 89.39||.||0.0||0.0||.||0.0||0.0|
|11A||4||2003||H. pinguifolia 'Sutherlandii'||.||.||0.0||.||0.0||0.0|
|11A||13||2003||H. venustula (Mt. Hikurangi)||.||.||0.0||.||0.0||0.0|
|11A||16||2003||H. buxifolia 'Minima'||.||.||0.0||.||0.0||0.0|
|11A||22||2003||H. sp. (diosmifolia x townsonii)||.||.||5.0||.||.||5.0|
|11A||25||2003||H. diosmifolia 'Prostrata'||.||.||5.0||.||.||5.0|
|11A||31||2003||H. sp. (harperi)||.||.||0.0||.||0.0||0.0|
|11B||1||2003||H. recurva 'Aoira'||.||.||2.3||.||3.6||3.0|
|11B||7||2003||H. 'Karo Golden Esk'||.||.||0.0||.||0.0||0.0|
|11B||16||2003||H. buchananii 'Fenwickii'||.||.||0.0||.||.||0.0|
|11B||22||2003||Parahebe linifolia 'Blue Skies'||.||.||3.0||.||2.0||2.5|
|12A||10||2003||H. glaucophylla 'Clarence'||.||.||0.0||.||0.0||0.0|
|12A||19||2003||Parahebe lyallii 'Baby Blue'||.||.||2.6||.||2.0||2.3|
|12A||22||2003||H. acutiflora (Huka Falls)||.||.||5.0||.||.||5.0|
|12B||13||2003||Karo Golden Esk'||.||.||0.0||.||0.0||0.0|
|12B||16||2003||H. sp. (Ilirilii)||.||.||3.0||.||2.6||2.8|
|12B||25||2003||H. pimelioides var. glauca 84.79||.||.||0.0||.||0.0||0.0|
|12B||28||2003||H. glaucophylla 'Korbel Pewter'||.||.||0.0||.||0.0||0.0|
|13A||13||2003||H. odora 'Baby Blush'||.||.||0.0||.||0.0||0.0|
|13A||16||2003||H. topiaria 'Rosewarne'||.||.||0.0||.||0.0||0.0|
|13A||19||2003||H. pubescens 90.486||.||.||5.0||.||.||5.0|
|13B||13||2003||H. parviflora 'Holdsworth'||.||.||0.0||.||0.3||0.2|
|13B||16||2003||Parahebe catarractae 'Porlock Purple'||.||.||2.3||.||2.0||2.2|
|13B||31||2003||La Favorite' 89.26||.||.||5.0||.||.||5.0|
|14A||13||2003||H. albicans (Gouland Downs)||.||.||0.0||.||0.0||0.0|
|14A||23||2004||H. venustula 'Patricia Davies'||.||.||.||.||0.0||0.0|
|14B||7||2003||H. sp. (procumbens)||.||.||2.0||.||0.0||1.0|
|14B||29||2004||Parahebe 'County Park'||.||.||0.0||0.0||0.0||0.0|
|15A||10||2004||H. elliptica 'Charleston'||.||.||.||.||3.3||3.3|
|15B||10||2004||H. recurva 'Boughton Silver'||.||.||.||.||1.5||1.5|
Note that the names of the plants appear in the chart as they were received. Some of these names are invalid or were incorrect when the variety was obtained and have since been corrected. Others were assigned to distinguish unidentified varieties obtained from a source. Contact the author for information about the identity of individual plants.
Flowering times of the Hebes in this trial were assessed monthly. Newly-planted Hebes are not assessed in the year of planting to allow for establishment. Flowering was rated on a 0-5 scale, with 0 meaning no flowers present and a rating of 5 given to those plants which are completely covered with blooms. The following chart shows flowering of the various clones in the trial. In many cases, flower data collection has been interrupted, or stopped, by cold weather affecting the plants.
|albicans (prostrate form)||XXX|
|Bishopiana Champagne||XXX||Tends to rebloom in Sept-Dec|
|boughton dome||Has no flowered|
|carnulosa||XXX||Blooms only after 4-5 years|
|Christabel'||Has not bloomed|
|Christensenii'||Has not bloomed|
|Clear Skies'||XXX||Data affected by Phytophthora problem|
|County Park'||No data|
|Cressit||Data affected by Phytophthora problem|
|Dobbies Delight||No data|
|Edinensis||Has not flowered|
|emerald gem||Has not flowered|
|Fairlane'||XXX||modest in bloom|
|Gloriosa'||XXX||XXX||XXX||Data incomplete because of cold damage|
|Gnome'||Has not flowered|
|Goeff. Turnbull'||XXX||winter injury affects results|
|great orme||XXX||XXX||reblooms sporadically through October|
|H. 'Affinis' 89.60||No data-winter killed|
|H. acutiflora (Huka Falls)||XXX||Data incomplete because of cold damage|
|H. albicans (Gouland Downs)||XXX|
|H. albicans 242-99||XXX|
|H. albicans 83.120||XXX||XXX||XXX|
|H. amplexicaulis||nbsp;||XXX||Not a strong bloomer|
|H. anomala||XXX||Not a strong bloomer|
|H. brachysiphon||XXX||XXX||Sporadic rebloom in Fall and Winter|
|H. buchananii 'Fenwickii'||Data affected by plant dieback|
|H. buxifolia 'Minima'||XXX|
|H. corriganii 91.663||XXX||XXX||XXX||XXX|
|H. cupressoides 'Nana' 89.23||Has not flowered|
|H. diosmifolia (Strybing H-15)||XXX|
|H. diosmifolia 84.75||No data-winter killed|
|H. diosmifolia 'Prostrata'||No data-winter killed|
|H. divaricata 84.76||XXX|
|H. elliptica||No data-winter killed|
|H. elliptica 'Charleston'||XXX||XXX|
|H. elliptica 'Variegata' (Strybing H-13)||No data-winter killed|
|H. evenosa||No data-winter killed|
|H. glaucophylla 'Clarence'||XXX|
|H. glaucophylla 'Korbel Pewter'||Has not bloomed significantly|
|H. imbricata||Has not bloomed|
|H. 'Karo Golden Esk' (11B)||Has not bloomed significantly|
|H. macrantha 91.631||XXX|
|H. macrocarpa 'Pink'||XXX||XXX||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|H. macrocarpa v. brevifolia||Data incomplete because of cold damage|
|H. macrocarpa v. brevifolia 84.78||Data incomplete because of cold damage|
|H. macrocarpa v. macrocarpa||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|H. ochracea 'James Stirling'||XXX||Blooms only after 4-5 years|
|H. odora 'Baby Blush'||XXX|
|H. parviflora 'Holdsworth'||Has not bloomed|
|H. parviflora v. angustifolia||Has not bloomed|
|H. pauciramosa var. masonae||XXX||Blooms sporadically throughout year|
|H. pimelioides var. glauca 84.79||XXX|
|H. pinguifolia 'Sutherlandii'||XXX|
|H. pubescens||XXX||XXX||XXX||Data incomplete because of cold damage|
|H. pubescens 90.486||XXX||XXX||Data incomplete because of cold damage|
|H. recurva 'Aoira'||XXX|
|H. recurva 'Boughton Silver'||XXX|
|H. rigidula (12B)||XXX|
|H. rigidula (7B)||XXX||XXX|
|H. rupicola||Has not bloomed|
|H. salicifolia v. angustissima||XXX||XXX||XXX||Blooms sporadically in fall|
|H. salicornioides 89.39||XXX|
|H. 'Silver Queen||Data incomplete because of cold damage|
|H. sp. (diosmifolia x albicans)||XXX|
|H. sp. (diosmifolia x townsonii)||Data incomplete because of cold damage|
|H. sp. (elliptica x crassifolia)||Data incomplete because of cold damage|
|H. sp. (Halifax Hardy)||XXX|
|H. sp. (harperi)||XXX|
|H. sp. (llirilii)||XXX||XXX|
|H. sp. (odora var. prostrata)||XXX|
|H. sp. (pinguifolia)||XXX|
|H. sp. (procumbens)||Has not bloomed|
|H. sp. (unknown clone)||XXX||XXX||Data incomplete because of cold damage|
|H. sp. (venustula)||XXX|
|H. sp. (Western Hills)||XXX|
|H. sp. 84.86||XXX||Data incomplete because of cold damage|
|H. Speciosa 91.612||Data incomplete because of cold damage|
|H. speciosa 'Pink'||XXX||XXX||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|H. speciosa 'Violacea'||XXX||XXX||Data incomplete because of cold damage|
|H. stricta v. lata||XXX|
|H. Stricta v. macroura||XXX||XXX||XXX|
|H. topiaria 'Rosewarne'||XXX||Minimal bloom so far|
|H. townsonii 91.747||Data incomplete because of cold damage|
|H. traversii||XXX||XXX||Data incomplete because of cold damage|
|H. venustula (Mt. Hikurangi)||XXX|
|H. venustula 'Patricia Davies'||Has not bloomed|
|H. venustula 'Sky Blue'||XXX|
|Hartii||XXX||Data incomplete because of cold damage|
|Heidi'||XXX||XXX||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|heliohebe hulkeana||XXX||Data incomplete because plant dieback|
|Hidcote'||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|Highdownensis'||XXX||Some rebloom in fall|
|Hinderwell'||XXX||XXX||XXX||Data incomplete because of cold damage|
|Hinerua||XXX||Only blooms after 4-5 years|
|Hobby'||XXX||Data incomplete because of cold damage|
|Inspiration||Data incomplete because of cold damage|
|Island Pass'||Has not bloomed|
|Janet||XXX||XXX||XXX||XXX||XXX||XXX||May continue to bloom in winter|
|Jasper'||Has only insignificant bloom|
|Joan Lewis'||XXX||XXX||Data incomplete because of cold damage|
|Karo Golden Esk' 12B||Has not bloomed|
|La Favorite' 89.26||Data incomplete because of cold damage|
|La Seduisante||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|Laingii 94.53||Has not bloomed|
|Lewisii||XXX||XXX||Data incomplete because of cold damage|
|Lindsayii'||XXX||XXX||Not a strong bloomer|
|little||XXX||XXX||XXX||Data incomplete because of cold damage|
|Loganioides||Has not bloomed|
|Louise'||Data incomplete because of cold damage|
|Maori Gem||Has not bloomed|
|Mary Antoinette'||XXX||Data incomplete because of cold damage|
|Mauve Fingers'||XXX||Data incomplete because of cold damage|
|mckean||Has not bloomed|
|Midsummer Beauty'||XXX||XXX||Data incomplete because of cold damage|
|Mount Stewart||Sporadically produces a few flowers|
|mrs winder||XXX||Flowers sporadically in summer and fall|
|Mystery Red'||Data incomplete because of cold damage|
|New Zealand Gold||Has not bloomed|
|nicolas blush||XXX||XXX||XXX||Flowers sporadically into December|
|Obtusata||Data incomplete because of cold damage|
|Oratia Gala'||XXX||Will flower sporadically into Fall|
|oswego||XXX||XXX||Flowers sporadically during Fall|
|Otari Beauty||XXX||Flowers sporadically during Fall|
|Otari Delight'||Data incomplete because of cold damage|
|Pamela Joy'||XXX||XXX||Data incomplete because of cold damage|
|Parahebe catarractae 'Porlock Purple'||XXX||XXX||XXX|
|Parahebe 'County Park'||Data incomplete because of cold damage|
|Parahebe formosa 90.178||Data incomplete|
|Parahebe lyallii 'Baby Blue'||XXX||XXX||XXX|
|Parahebe linifolia 'Blue skies'||XXX||XXX||XXX||XXX|
|Pascal||XXX||Flowers sporadically in Fall|
|patty's purple||XXX||Flowers sporadically later in summer|
|H. sp. ('Patty's Purple Variegated')||Data incomplete because of cold damage|
|paula||Data incomplete because of cold damage|
|Pimeba||Data affected by plant dieback|
|Pink Fantasy||XXX||Flowers sporadically throughout Fall|
|Pink Paradise (PVR)||XXX||XXX||XXX||XXX||XXX||XXX|
|Pinocchio'||Data incomplete because of cold damage|
|powis castle blue||XXX||XXX||Data incomplete because of cold damage|
|Primley Gem||XXX||Data incomplete because of cold damage|
|prince||XXX||Flowers sporadically throughout Fall|
|purple queen||Data incomplete because of cold damage|
|Purple Shamrock'||Has not bloomed|
|Purple Tip||XXX||XXX||Data incomplete because of cold damage|
|Quicksilver||XXX||Data affected by Phytophthora problem|
|Red Edge||Data incomplete because of cold damage|
|Sarnia||XXX||XXX||XXX||XXX||May continue to bloom in winter|
|Silver Dollar'||XXX||Sparse bloom, prone to reversion|
|Simon Delaux||XXX||XXX||Data incomplete because of cold damage|
|Snow wreath||Data incomplete because of cold damage|
|Snowdrift'||Data incomplete because of cold damage|
|speciosa||XXX||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|speciosa variegata||Data incomplete because of cold damage|
|Strybing H-1||XXX||Data incomplete because of cold damage|
|Strybing H-10||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|H. sp. (Strybing H-17)||Has not bloomed|
|Strybing H-2||No significant bloom|
|Strybing H-4||XXX||Data incomplete because of cold damage|
|Strybing H-5||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|Strybing H-8||XXX||XXX||XXX||XXX||XXX||XXX||Data incomplete because of cold damage|
|topiaria||XXX||Not a heavy bloomer|
|tricolor||Data incomplete because of cold damage|
|H. venustula 'Patricia Davies'||Has not bloomed|
|Veronica Lake'||Data incomplete because of cold damage|
|Violet snow||XXX||XXX||XXX||Flowers sporadically throughout Fall|
|Walter Buccleaugh'||Has not bloomed|
|White Gem||XXX||XXX||Flowers sporadically throughout Fall|
|wiri cloud||XXX||Not a heavy bloomer|
|Wiri Dawn'||XXX||XXX||Data incomplete because of cold damage|
|Wiri Gem||XXX||Data incomplete because of cold damage|
|Wiri Gem 94.56||XXX||Data incomplete because of cold damage|
|Wiri Magic'||Data incomplete because of cold damage|
|Wiri Prince'||Data incomplete because of cold damage|
|Wiri Spears' 94.61||Data incomplete because of cold damage|
|Wiri Splash||Data incomplete because of cold damage|
|Wiri Vision||Data incomplete because of cold damage|
Note that the names of the plants appear in the chart as they were received. Some of these names are invalid or were incorrect when the variety was obtained and have since been corrected. Others were assigned to distinguish unidentified varieties obtained from a source. Contact the author for information about the identity of individual plants.
Pests and Diseases
Few pest problems were noted in this trial. From time to time, spittlebugs can be seen on the plants in spring, but do no obvious damage.
Earwigs can burrow between the clasped leaves at shoot tips on large-leaved cultivars, and their feeding causes some leaf distortion, but this is sporadic and relatively minor damage.
Whiteflies may be seen on the plants, but this seems to be rare. Other common pests of landscape plants, like root weevils or aphids, were not observed.
Although they are far from a pest, it should e mentioned that honeybees and other pollinators are very attracted to Hebes. They are to be found on the flowers most times of the year when they are active, but are particularly noticeable in the fall when few other plants are in bloom. Large, fall blooming Hebes will be host to large numbers of honeybees on warm days in late September and October.
Diseases have been more problematic in this trial. The major disease problems have been Septoria leaf spot, Downy mildew and Phytophthora Root Rot. To find out information on management of these diseases in the PNW, see the Pacific Northwest Plant Disease Management Handbook.
Septoria leaf spot
This is a fungal disease caused by Septoria exotica. The disease causes small black spots on the leaves, which enlarge and form an ash-colored center. Individual leaves may have large numbers of these spots. The disease is particularly noticeable on large-leaved cultivars, but can be seen on smaller-leaved types as well.
The spots become obvious in the late fall and winter on the current seasons growth. The following spring, as the new growth emerges, those affected laves tend to fall off. Over several years, repeated cycles of infection and leaf loss causes a “leggy” appearance to the plant, which can sometimes be temporarily corrected by pruning. Although a formal evaluation has not been done, a wide range of Hebe cultivars seem to be susceptible to the disease.
This is a fungal disease, caused by Peronospora grisea. The disease causes major leaf damage, leaf loss and shoot dieback, eventually it can cause plant death. The disease is usually noticed first by a yellowish, blotchy discoloration of the leaves, often on the lower leaves of the plants. This discoloration can affect large portions of individual leaves. Leaves become curled and distorted. On the underside of the leaves a grayish sporulation of the fungus may be seen.
Eventually the affected parts of leaves turn brown and shrivel. Plants can be entirely defoliated and killed.
This disease is a serious problem for cultivation of some Hebes in the landscape in the U.K. In western Oregon, it is generally not a problem for landscape shrubs in the Willamette Valley, assuming they are given sufficient light and air circulation. The only time it seems to occur in this area is if a Hebe is grown in too much shade in a moist environment. On the Oregon Coast, persistent summer fog can induce the problem in nursery or landscape situations.
Both Phytophthora sp. and Fusarium oxysporum and been implicated in root rot problems of Hebe. Phytophthora tends to be more of a problem in cold soil, while Fusarium is more common in warm soils. The disease is usually first noticed by the flagging of individual stems, often in mid-summer. Leaves on these stems turn yellow then brown. Entire sections or sides of the shrub may become affected quite rapidly, looking almost as though it were burned.
Plants may be stunted. Roots below affected branches are rotted. The entire plant may die, or it may persist for months in this state. Phytophthora in particular is more likely to be an issue in heavy-textured soil or poorly-drained sites. Amending these soils with organic matter and other amendments will improve soil aeration and reduce the likelihood of disease. Ensure the site is well-drained and water regularly but not to excess. Most established Hebes growing in good soil require water only 1-2 times per week for a few minutes from a typical irrigation system.
Hebes are often referred to as “drought-tolerant” shrubs and may be sold by retailers as such. However, even in the Pacific Northwest, summers are warm and dry enough to stress virtually all Hebes if regular summer water is not provided. This is particularly true of summer and fall-blooming cultivars, which bloom on new growth, and require regular water to continue growing, without which they will stop producing flowers.
How Hebes came to be regarded as “drought-tolerant” is a bit of a mystery, unless there is a tendency to associate evergreen plants in general with drought tolerance. The term “drought-tolerant” can mean a lot of different things, but if we use the definition, “a plant which will survive in the PNW entirely on rainfall without added summer irrigation”, then few Hebes will perform well under these conditions. The PNW is a Mediterranean-type climate, with a pronounced dry period of 3-4 months, and summer temperatures will exceed 90°F in the Willamette Valley on 14-21 days each summer. Almost all Hebes are from New Zealand, and therefore originate in a relatively mild, cool climate with at least some summer rainfall.
Kristensen (1989) classified Hebe species as to their origin in wet or dry habitats. About 1/4 of the listed species evolved in dry habitats. This includes familiar species like H. pinguifolia, H. carnosula, H. rakaiensis, H. decumbens, H. pimelioides and H. cupressoides. However, even the “dry” habitats received up to 60cm of rain per year. As a result, most of the available cultivars share this need for at least occasional summer water, depending on conditions. It is almost impossible to say what the water requirement of a particular cultivar will be, because many are of unknown parentage. Instead it will simply have to be planted and evaluated in the conditions characteristic of that site.
Symptoms of drought stress are expressed in a variety of ways. The first signs are typical of most plants and involve drooping of leaves and even shoot tips.
This is reversible if water is immediately provided. Repeated events like this will cause the leaf color in many Hebes to change from a glossy green to a pale, dull appearance, particularly on the older leaves.
Prolonged stress will cause yellowing of the foliage, and brown, necrotic areas will develop on the leaves, especially on the midrib.
The older leaves on the bottom and interior parts of the canopy will start die and fall off, in many cases giving the plant a “leggy” appearance.
Continued lack of water will cause dieback of portions of the canopy and eventually the entire plant.
Factors which will determine how much water a given Hebe will require are many:
Some Hebes do survive and grow well with limited water. Although evidence is scant, and based primarily on casual observation, in general blue-leaved Hebes seem to tolerate dryer garden conditions in the PNW than whipcord or large-leaved cultivars. Even these plants will still prefer a good watering every 7-10 days in the warmest part of summer and should not be planted with truly drought-tolerant Mediterranean plants like Ceanothus, Cistus or Rosemary, which are best without summer water.
The site will have a major impact on water requirement. Hebes planted in full sun naturally require more water than those in some shade. Plants on the south or west side of buildings will be particularly stressed from the added heat from the building. If protection from mid- to late-afternoon sun is provided, then water requirement will be reduced. Do not plant in full shade as this will result in poor growth and possibly foliar disease problems.
Soil is another important factor and all Hebes prefer a well-amended, well-drained soil for best growth. Heavy, compacted soils do not allow for good root growth of fibrous-rooted plants like Hebes and this will increase drought stress. Amendment of these soils with organic matter prior to planting is a good start. Mulching following planting, and avoiding foot traffic on the soil afterward, will help good structure to develop and improve conditions for root growth and water storage in the soil. For more information on soil amendment and mulching, see EC 1561, Improving garden soils with organic matter, or EC 1629-E, Mulching woody ornamentals with organic materials. Both are available from OSU Extension publications: http://extension.oregonstate.edu/catalog/.
OSU Extension Service
Marion and Polk Counties
3180 Center Street NE #1361
Salem, OR 97301
Kristensen, L. 1989. The Genus Hebe-A botanical report. Danish Research Service for Plant and Soil Science. Report #S-2034.
Books and websites
There are now several excellent texts on Hebes, which are essential for those concerned with correct naming of species and cultivars, as well as being sources of information on culture of these plants:
Bayly, M and A. Kellow. An illustrated guide to New Zealand Hebes. Te Papa Press.
Chalk, D. 1988, Hebes and Parahebes. Timber Press, Portland, OR. 152 pp. (out of print)
Hutchins, G. 1997. Hebes here and there. Hutchins and Davies, Reading, Berks. 320 pp.
Metcalf, L.J. 2001. International Register of Hebe cultivars. Royal New Zealand Institute of Horticulture. 232 pp.
Metcalf, L. 2006. Hebes: a guide to species, hybrids and allied genera. Timber Press, Portland, OR. 260 pp.
Wheeler, Chris and Valerie. 2002. Gardening with Hebes. Guild of Master Craftsman Publications. 160 pp.
Another fundamental source of information on Hebes is The Hebe Society, whose website has a wealth of information and links. http://www.hebesoc.org