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| 3.3.6 |
Design Considerations for Landscaped Spaces |
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| Most people find soft landscaped areas appealing. In external spaces, planting of natural elements means more than cosmetic landscaping treatment to achieve a certain visual effect, or just to screen or improve the aesthetics of built elements. Soft landscaping plays an important role in enhancing our overall outdoor environment. By early planning and concerted effort of designers and all stakeholders, soft landscaping can fulfil various functions such as creating a sense of a place, indicating the flow of circulation or orientation, and meeting the therapeutic needs of specific user groups. |
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| (a) |
Selection of planting materials |
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Basic knowledge in plant anatomy is vital in landscape design (3.3.6.1a). There are quite a few plants that contain toxins or irritant substances in the natural outdoor environment. In Hong Kong, there is a wide range of such plants, trees, shrubs and climbers, etc. The symptoms of toxicities may range from allergies to potentially fatal poisoning risks. Ways of coming into contact with such plants are varied, and include ingestion and direct skin contact. Due care is therefore required in selecting and positioning the plant species that are within easy reach and in places where sensitive users are expected. |
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Future maintenance of the selected planting should also be considered. If there are any special maintenance requirements, they should be conveyed to the future operator or management team. |
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Competent knowledge in both horticulture and physiology of plants is required in the selection of planting materials for landscape design. With sensible judgment, cautious design detailing and appropriate management, some of the plants that contain toxins can still be used in our external landscaped spaces. For instance, Oleanders, (Thevetia peruviana, Nerium oleander) common shrubby plants, are often used in roadside planting in Hong Kong and other Mediterranean countries for their hardy and pollution-resistant properties (3.3.6.1b). |
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Warning signs may sometimes be required in tourist spots or public parks to identify the plants. For example, overseas visitors or local children may mistake the poisonous fleshy fruits of Cerbera (Cerbera manghas), a selfseeded indigenous tree commonly found on beaches, for Mango (Mangifera indica), an edible tropical fruit (3.3.6.1c). |
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Many plant species feature dispersal of seeds and/or pollens by wind. Some of those plants may cause potential health problems if they are planted over a large area where sensitive users are expected. For instance, the ubiquitous forestry plantation of Tsugi (Cryptomeria japonica) in many Japanese cities has caused problems of hay fever in early spring. Other species with wind-borne seeds such as Willows (Salix spp.) and Cotton Trees (Bombax ceiba) may cause similar problems (3.3.6.1d). If possible, use of these plants near facilities such as hospitals and schools should be avoided since the users are likely to be sensitive to them. |
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The morphology of the plants should be considered in amenity planting design. Leaves or stems of some trees, shrubs or ground covers with sharp spikes render them unsuitable for planting at easily accessible areas, e.g. planters within children play areas, hedges along the access routes in public spaces, etc. (3.3.6.1e). |
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| Sapium sebiferum (Chinese Tallow Tree), a commonly found native tree, has high amenity value with its spring/autumn colour, ecological importance to wildlife and other economic value. The bark and seed oil, however, are toxic |
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| 3.3.6.1a Rhus succedanea (Wax Tree), an indigenous tree, contributes to the natural landscape with its autumn leaf colours in our countryside. If tree sap comes into contact with the skin, it may cause skin irritation to some sensitive persons |
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| 3.3.6.1b (left) Thevetia peruviana (Yellow Oleander); (right) Nerium oleander (Oleander) |
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| 3.3.6.1c (left) Cerbera manghas (Cerbera); (right) Mangifera indica (Mango) |
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| 3.3.6.1d Flowers and seeds of Bombax ceiba (Tree Cotton) |
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| 3.3.6.1e Some ornamental plants have spiky leaves or thorny stems |
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| (b) |
Positioning of planting materials |
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Safety Concern: Low-branching trees should be regularly maintained with appropriate arboricultural practices, such as branch trimming or canopy lifting, so that they will not protrude onto seating areas or access routes. Similarly, climbers or trailers planted over the entrance gates or along footpaths should be regularly attended to (3.3.6.1f). A minimum clear height of 2 metres should be maintained; this is particularly important to protect those with visual impairment. |
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Sensory Qualities: Planting should be arranged in appropriate locations and heights such that they can be appreciated at their best angles (3.3.6.1g). The positioning of different planting materials such as trees, shrubs, groundcovers, etc. should not be dictated by aesthetic concerns alone. The sensory qualities of plants should also be considered during the planting design stage. In fact, different plant species have their own distinctive qualities in landscape use. Apart from giving visual/aesthetic merits (such as bright colour flowers), a tree species can be selected for a particular location for its shading effect; foliage texture; fragrant blossom/foliage; edible fruits; unique bark texture; or auditory effects of rustling foliage in the wind. In Hong Kong, many of the commonly found plants have multiple sensory qualities. The atmosphere of a place (genius locus) can be most effectively and distinctively created by making full use of the sensory qualities of the plants. Refer to Figure 3.3.6.1h for details. |
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Visual Accessibility: In most situations, it would be beneficial to bring the planting to the sightline of people while they are seated or when they are walking along a travel path. Amenity planting should take full advantage of the site condition, especially when there are potentially attractive vantage points nearby, so that the soft landscaping can complement its surroundings. In the urban areas, apart from the usual sightlines at ground level, those from high-rise buildings, podiums, elevated pedestrian walkways, etc. should also be considered when designing amenity planting (3.3.6.1i). |
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Physical Accessibility: If a planting or lawn area is intended to be physically accessible by visitors, a good design approach is to raise the lawn or a portion of that area to an accessible height. This will enable wheelchair users, as well as those park-goers who have difficulty in sitting and/or bending their knees to be within reach of the planting or lawn area and have the same tactile experience enjoyed by others (3.3.6.1j). Such raised lawn should also be provided with an accessible route so that all users can go on it. |
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| 3.3.6.1f In public open spaces, tree branches or vigorous vine should not protrude onto the circulation spaces |
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| 3.3.6.1g Good design is required to display the unique sensory qualities of different plants in appropriate locations and at the best vantage points |
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| 3.3.6.1h Three important aspects contributing to the sensory qualities of planting |
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| 3.3.6.1i Visual access to the landscaped areas should be considered in the landscaping design |
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| 3.3.6.1j Raised planting or lawn areas can facilitate physical access by people with different abilities |
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| (c) |
Practicality and sustainability |
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Many people find plants with colourful blossom, contrasting texture, and distinct foliage very attractive; people with low vision can also appreciate them. During summer time when tropical rainstorms are frequent, hardy groundcovers with bright colour foliages can be used to achieve a similar effect, but without the intensive attendance and high maintenance costs (3.3.6.1k). When planting on a large site area, contrasting effects in colours and/or texture offered by the relatively long-lasting foliages can be considered rather than seasonal blossoms. |
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Seasonal flowers are best seen in groups/bands and within close physical distance to the viewers. To reduce resources required for maintenance, different species or cultivars of herbaceous plants in consecutive life cycles should be used to prolong the blooming period (3.3.6.1m). |
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| 3.3.6.1k Attractive planting can be achieved with different approaches |
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| 3.3.6.1m Seasonal flowers are best seen in groups/bands and within close physical distance to the viewers |
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| (d) |
Safety aspect and public hygiene |
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All natural vegetation attracts wildlife to a certain extent. Abundant blossoms or fleshy berries in particular attract birds, bats, or insects such as butterflies, bees or wasps (3.3.6.1n). Careful selection of plants as well as proper management control is therefore vital in the design and operation of public landscaped areas. Where exposure to risk is high in the countryside, appropriate multi-media signage should be provided to give warning (3.3.6.1p). |
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Some groundcovers or shrubby plants feature vigorous growth and have positive amenity attributes. By producing fast-growing vegetation covers, they are valuable in erosion control. However, plants with this special growing habit cause vermin problem if left unattended. For example, Wedelia trilobata, a commonly used roadside plant, features an abundance of attractive yellow flowers (3.3.6.1q). If planted extensively, regular cutting would be required to avoid undesirable thatching effect. |
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| 3.3.6.1n Some plants have fruits and berries attractive to birds, bats or insects, for example Punica granatum (Pomegranate) and Melia azedarach (China-berry) |
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| 3.3.6.1p A warning sign with message in written text, Braille, and graphics |
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3.3.6.1q Plant the right species in right place with appropriate maintenance and management |
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| (e) |
Horticultural operations |
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Natural vegetation, including amenity planting, requires regular attendance for upkeep and maintenance. In carrying out routine horticultural operations, the following best practices for universal accessibility should be noted: |
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When pruning is required for trees planted near a walkway/footpath or near play/exercise areas, the branches should be properly trimmed according to good arboricultural/horticultural practices and be finished without any sharp edges that could form a safety hazard (3.3.6.1r). |
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Regular pruning/trimming is required to ensure adequate clearance without any obstruction to crucial sightlines and passageways. Hedges along access route and at the junctions of passageways should always be kept below the sightline of wheelchair users and small children. Vegetations should not obstruct other functional provisions such as illumination, handrails, and signage, etc. (3.3.6.1s). |
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If staking is required after tree planting, the metal or bamboo stakes should not have any exposed sharp edges or pointed ends. Any ties and wires should be appropriately placed to avoid tripping hazard if they are installed within reach of children playgrounds or sittingout areas, etc. Bamboo poles used as tree stakes should be properly dressed and finished, and the top end should be sealed off to prevent mosquito breeding (3.3.6.1t). |
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Temporary closure may be required during and after certain horticultural operations such as application of fertilizer/pesticide, particularly at lawns or planting beds within activities areas such as children playgrounds and ball courts, etc. Adequate warning signs should be provided accordingly (3.3.6.1u). |
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Proper tree maintenance with good arboricultural practices is required in avoiding potential hazards. Slanting trees growing within accessible areas should be treated with care, especially during and after typhoons. Remains of tree stump in tree pits within access routes should be properly removed and the surface should be promptly reinstated (3.3.6.1v). |
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To improve visual accessibility and form a unique tactile experience, special horticultural practices can be adopted to create distinct feature planting. Examples worth exploring are espalier, topiary, pleached trees and plashed hedges (3.3.6.1.w). |
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| 3.3.6.1r Pruning works should be done correctly |
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3.3.6.1s Vegetation should not obstruct any crucial sightlines, passageways, or any other functional provisions |
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| 3.3.6.1t Some good examples of proper staking |
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3.3.6.1u Warning sign on planting treated with pesticide |
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| 3.3.6.1v Proper tree care is essential in avoiding potential hazards |
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| 3.3.6.1w Different horticultural practices can be adopted to create visual and tactile interest — espalier on wall, topiary in a park, pleached trees at sitting areas and plashed hedges along footpath |
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