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/hebe/ - Plantaginaceae

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Horticulture and the goddess of youth

c46fbd No.132447

> 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.


c46fbd No.132448

> 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.

c46fbd No.132449

> 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.

> http://www.usbr.gov/pn/agrimet/

c46fbd No.132450

> 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.).

c46fbd No.132451

> 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.

c46fbd No.132452

> 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.

c46fbd No.132453

> 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.

c46fbd No.132454

> 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.

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