Perform search

                    Create a biodiverse streetscape

                    A wide nature strip which has recently been planted in rows

                    ​A newly planted biodiverse streetscape along Docklands Drive, Docklands
                    Streetscapes are challenging environments for plant growth. To maximise the chances of successfully making an attractive, biodiverse planting at these sites, you need to take the time to analyse and prepare your site, plan your planting and develop a maintenance plan.

                    Planting in a streetscape environment is usually more complex than a parkland environment. The streetscape needs to serve the movement needs of vehicles, cyclists and pedestrians, allow access to adjacent properties, and carry overhead and underground services. The road verge is where weekly rubbish removal takes place. It often includes signage, telephone poles, as well as trees. 

                    Streetscapes are generally highly disturbed landscapes that can be hostile to plant growth and performance. Adverse factors include soils with altered chemical and physical properties, particularly compaction and permeability; small soil volumes for planting; low maintenance and resource inputs; the need to manage traffic to conduct maintenance; and constraints from the placement of services or adjoining infrastructure.

                    Failure to recognise the tough realities of the streetscape can result in dead, poorly performing or unattractive plantings that create a negative perception of urban vegetation, increase maintenance inputs, including replacement, and create poor quality, unsustainable urban landscapes.  

                    To maximise the chances of successfully making an attractive, biodiverse streetscape planting, it is important to:

                    1. Analyse the site.
                    2. Prepare the site for planting.
                    3. Select plants using clear criteria and design.
                    4. Develop a maintenance plan.
                    5. Consider using additional habitat elements.

                    1. Analyse the site

                    The best approach to establishing a biodiverse streetscape will be influenced by surrounding infrastructure, aspect, shade, soils, existing vegetation and the need for irrigation. Analysis should focus on determining what can be realistically changed to increase the success of the planting, and on ensuring that the selection of plants can tolerate the site's environmental, physical and maintenance constraints.

                    Site conditions are especially important to understand in areas that can’t be significantly improved, such as beneath tree canopies (for example, where tree roots may get damaged by excavation) or where adjacent patches can’t be treated (for example, turf that is likely to invade). In some cases, retrofitting a streetscape site for biodiversity planting may be impractical, for instance due to contamination or high weed loads in the existing soil and the high cost of excavation and disposal.

                    Soils

                    ​Some analysis of the site’s soil is critical. This includes assessment of the underlying soil texture and profile and looking for any evidence of possible soil problems. Excess nutrients in the soil can cause significant problems because they promote rapid weed growth, while elevated phosphorus levels can be toxic to many native species. Extremes of pH (high or low acidity) or the presence of salinity in the soil will also affect which species will grow well. Physical problems like compaction and layering are most prevalent in clay soils and can lead to reductions in root growth, water movement, and drainage and soil oxygen. 

                    There are several simple tests that can be used to evaluate soil prior to planting. Start with a ‘screwdriver test’ to gauge soil compaction. This includes driving a 200–300 mm long screwdriver or steel rod into the dry soil. A non-compacted soil should show only some resistance to penetration of the screwdriver for a considerable depth, while a compacted soil will be difficult or impossible to penetrate beyond a few centimetres. Digging a small hole, no more than 30 cm in depth, on the site can reveal much about the soil’s physical properties. Look carefully across the profile for the presence of topsoil and subsoil layers, as well as the presence of any impervious layers or impurities like rubble or organic materials at depth. Test some of the soil by rolling it into a ribbon to determine its texture (clay, sand, loam, etc.). Soil pH is easily tested using a simple colorimetric dye test. 

                    Finally, fill the hole to half its depth with water and observe its drainage. If it drains quickly after 15 minutes, then it will likely retain little water; however, if most of the water has not drained after 30 mins, it means that the soil will likely be readily waterlogged. 

                    Having some knowledge of the history of the site will help to determine whether further analysis and possible remediation is necessary, particularly laboratory testing to assess soil chemical properties.

                    Vegetation

                    ​The existing vegetation on site should also be identified. Critically, this must include evaluation of any weeds present, particularly the presence of perennial or highly competitive weeds, such as stoloniferous grasses (grasses that put out suckering runners, like  couch grass) and geophytes (plants with underground storage organs such as onion grass (Romulea rosea) or Oxalis sp). These can readily overtake a planted site and can have dramatic effects on vegetation success, particularly on smaller and open native herbaceous species (plants that do not have a woody stem such as forbs and grasses). Be aware that because of plant dormancy, generally over either winter or summer, not all the weeds present may be visible at certain times of the year.

                    The weed seedbank

                    ​It is also crucial to assess the weed seedbank present in the soil. The only accurate way to assess the weed seedbank is to take samples, germinate the seeds present and identify the species, a process which is time consuming and requires expertise. It is generally better to simply note the extent to which weeds are present, and to assume that the soil will contain substantial quantities of seeds from those species. Older soils are likely to have significant amounts of weed seed.

                    Some sites can be treated by repeated application of contact or systemic herbicides, although this can take many months. In other sites the only certain practical method for removal of the weed seedbank is to remove the soil itself. New methods, such as soil steaming or pine oil treatments, are still experimental and not proven to be effective in many landscapes.

                    Even ‘new’ soils from commercial suppliers can contain weed seed, which can be blown-in during the period between manufacture and delivery or be present in any ‘mined’ components used in the soil manufacturing process. Weed seeds can also be present in organic mulches produced from garden waste or tree chippings. To minimise risk, only use quality suppliers of soil and mulch, and ensure soils comply with AS4419-2003 Soils for Landscaping and Garden Use (Natural soil/soil blend), and organic mulches with AS4454–2012: Composts, soil conditioners and mulches.

                    ​2. Prepare the site for planting

                    Preparing the site for a streetscape biodiversity planting is often different to standard specifications for many council plantings, such as trees, nature strips or uniform traffic treatments. The objective is to ensure that the conditions, and particularly the soils, favour the predominantly indigenous or native planting mix. Site preparation must also consider the available maintenance inputs during establishment and over the lifetime of the project.

                    Ripping to relieve compaction

                    ​If the site has compacted soil, for example in areas where there has been extensive prior use of heavy machinery, especially in clay soils, some remediation will be needed before any planting takes place. Decompaction treatments help to increase soil oxygenation, water infiltration and drainage. Ripping the soil with a chisel plough or mouldboard plough is preferable to using rotary hoes because they can be problematic in clay soils. Be aware that ripping can bring weed seed to the soil surface, promoting germination. For this reason, ripping should only be undertaken where necessary, that is, when the soil is compacted.

                    Scalping and scoria: topsoil may not be the best ‘soil’ to use

                    ​While the addition of ‘topsoil’, generally to a depth of 150 to 200 mm, is often a standard treatment to prepare streetscape sites for planting, for streetscape biodiversity plantings the best outcomes may be obtained by changing the profile completely. 

                    Native plants tend to be adapted to soils that have low nutrient levels. By planting native species in low-nutrient soils, the native species are more readily able to out-compete exotic weeds, meaning that the planting is more likely to succeed and require less maintenance to do so. Therefore, adding ‘topsoil’ may be counterproductive to establishing a streetscape biodiversity planting.

                    Another factor to consider is that the top layer of soil is usually where the bulk of the weed seedbank is located. 

                    Scalping is a process in which the top layer of soil is removed, usually to a depth of 100 to 200 mm. By removing this layer, the abundance of exotic weeds requiring removal during the future planting’s maintenance will be considerably reduced. Scalping has the additional advantage of exposing the subsoil, which tends to be much lower in its nutrient levels than the topsoil that has been removed. Being a low-nutrient soil, the subsoil can become a planting bed that favours native species. In heavy clay soils some amelioration to the subsoil may still be necessary to ensure plants can grow successfully.

                    Because scalping reduces the surface level, height may need to be made up, especially if hard edges such as kerb and channel are present. This can be done with the addition of a mineral-based planting substrate such as sand, gravel or scoria. Because these are mineral based, they are low-nutrient, and provide a poor substrate for weeds to become established.

                    The use of such low-nutrient mineral substrates as ‘soil’ has been shown to be effective in favouring indigenous vegetation. An example is the biodiverse streetscape planting at Docklands Drive, Docklands where 200 mm deep scoria (8 mm aggregate including fines) has been used as the planting substrate. 

                    Some issues to consider are:

                    • Mineral-based planting substrates vary significantly in their properties and applications and need to be carefully specified.
                    • Some care is needed with scalping in heavier soils, especially when using machinery, and scalping should always be followed by some light cultivation prior to the addition of any additional soil, if being used, or prior to planting.
                    • If planting into a scoria substrate, additional irrigation will be required in the first season or two until plants establish roots in the subsoil. Otherwise significant plant losses are likely to occur.
                    • Some plantings may also benefit from the addition of a small amount of organic matter such as composted coir or aged pine bark.
                    • If topsoils are used, they should comply with AS4419-2003 Soils for Landscaping and Garden Use (Natural soil/soil blend), although compliant soils could still have elevated nutrients and significant weed seed banks that, over time, could be disadvantageous to many of the native plants recommended in this guide. 
                    • Removal of scalped soil may be problematic if the soil is considered to be contaminated, for instance with high lead levels from historic use of leaded petrol.
                    • Subsoils can be used instead of mineral additions to make up height following scalping.
                    • When using mineral additions, care should be taken that they do not spill out onto pavements, where loose pieces can act as trip hazards.

                    Treating weeds

                    Some treatment of weeds is crucial to planting success. An assessment of the weed flora present will help determine which weed treatments will be most successful. Scalping may assist in reducing the weed seed bank and nutrient-rich topsoil unfavourable for native plant growth. Repeated herbicide applications, with a long-lead time before planting, have been shown to be very effective in reducing persistent weeds in planting sites. Where this is not possible, a single herbicide application, followed by use of woodchip mulch to 75–100 mm deep and fallowing for a minimum of six months prior to planting, is the best solution. Some follow-up weed control may be necessary during the fallow period. 

                    Make sure the woodchip mulch used meets Australian Standard AS4454-2012 Composts, soil conditioners and mulches. If possible, consider edge design that minimises the loss of mulch, especially from narrow beds. Be aware that maintenance staff need to be trained in identifying native species so that herbicide application does not result in off-target losses.

                    3. Select plants using clear criteria and design

                    The arrangement and composition of plants is important in establishing and sustaining a diverse planting. Some care is needed to ensure that suitable plant combinations are arranged with comparable growth habits and vigour. This is particularly important when a diverse planting outcome is sought. 

                    Many low-maintenance urban plantings, such as streetscapes, are readily dominated by groundcovers. This works well when large blocks of the same plant are being used, but often fails when more diverse planting outcomes are being sought. Consider using dominant or ‘functional’ groundcovers carefully in these combinations as they can readily overtake slower growing and more delicate plant species. 

                    Dense planting has been shown to improve the establishment of native vegetation in many urban sites.

                    When selecting plants to support biodiversity, it is important to choose a variety of species that flower at different times of the year. This will produce vegetation with a continuous pollen and nectar supply for bees, butterflies and birds, and other resources such as fruits and seeds. As well as providing a year-round food supply for biodiversity, this will sustain the aesthetic appeal of the streetscape plantings for longer periods.

                    Zoning

                    ​‘Zoning’ species means grouping them with other species that are comparable in growth habit, vigour or maintenance needs, and it is a useful way of organising a planting plan. Zoning can also involve grouping plants together that provide similar biodiversity resources to promote efficient foraging and use by local fauna, for example, by grouping individuals of the same species so that food resources are abundant in a specific area of planting. To further promote fauna foraging efficiency and benefit specialist species, plant many individuals of a few species, rather than a few individuals of many species.

                    Using groundcovers

                    ​Groundcovers are the species most commonly used in streetscapes, but encompass many different plant types, life-forms and habits, and the term ‘groundcover’ can be confusing in the context of landscape use. Groundcovers tend to be vigorous, evergreen and perennial plants with some degree of ‘canopy’ density to ensure thick coverage. 

                    ‘Functional’ groundcovers will be the most useful in streetscapes. These are robust, resilient plants that grow more than 300 mm in height, and many have specialised stems (rhizomes, stolons, suckering) to increase their coverage. Functional groundcovers typically have a dense, continuous layer of foliage (‘canopy’) which, together with their height, helps suppress weeds. Their often broad range of environmental tolerances and low maintenance needs makes them highly adaptable. 

                    These include woody plants, such as prostrate shrubs (for example, Correa, Thyptomene), shrubs with suckering stems (for example, Rhagodia) and even climbing plants (for example, Hibbertia scandens). A range of herbaceous (non-woody) plant lifeforms also work as functional groundcovers in streetscapes, including tufting or tussock-forming grasses and sedges (for example, Poa, Lomandra, Themeda) and vigorous, rhizomatous, grass-like plants (for example, Dianella, Stypandra). 

                    ‘Decorative’ groundcovers are slower or lower growing plants, growing less than 200 mm (although flowers can be taller), which often have a more open growth habit. Their slower growth and open habit make them less able to exclude and compete with weeds. They often have a more aesthetic role in a diverse planting and can require more maintenance. 

                    'Decorative' groundcovers include low-growing herbs and sub-shrubs (for example, Chrysocephalum, Pelargonium, Salvia) and more upright growing forbs (for example, Wahlenbergia). These types of plants, especially herbaceous species, tend to have shorter life-spans, lower survival rates, lower rates of establishment and provide less cover compared to the more robust and vigorous functional groundcovers.

                    Functional groundcovers can be used to create a ‘structural’ planting that can be used to surround and buffer decorative groundcovers. They are better able to prevent weed germination and establishment at the edge of the planting site and often cope more effectively with other edge effects such as wind, reflected heat from the pavement, pedestrian foot traffic and the impacts of dogs.

                    Availability of stock

                    ​Be aware that unusual or uncommon plant species need to be ordered well in advance (for example, 12 months), or contract grown to ensure availability and to avoid planting delays. Ensure substitutions are not allowed and stock is inspected upon delivery, otherwise substituted species may not perform or survive adequately or provide the desired biodiversity resources.

                    Tubestock can be better

                    ​It’s a common misconception that larger plant stock will grow more quickly than smaller plant stock. Often the reverse is the case. Provided there is good site preparation and maintenance, the use of tubestock is preferred over larger containerised plants because they grow much more quickly than mature plants post-planting, overtaking them in a few years. However, in sites with high pedestrian traffic, larger stock may be more obvious and deter and survive trampling more effectively until established. 

                    Direct seeding

                    ​Direct seeding has not been rigorously trialled in a streetscape environment, and no advice on the best approach can be given with any certainty here. Nevertheless, direct seeding may be a cost effective way of establishing streetscape biodiversity plantings, particularly on larger streetscape components such as wide nature strips and medians, or on large roundabouts. Native seed of many of the grass and some herb species listed in the Urban Nature Planting Guide are available from specialist native seed producers. 

                    The seed is produced in specialised nurseries from cultivars of known provenance that have reliable germination rates. Seed can be incorporated into a mix and applied using a variety of methods. It is important that the receiving seed bed is well prepared, for example, scalped, and low in nutrients.

                    Planting densities

                    ​It is important to plant at the right spacing in order to achieve full cover and to best supress weeds. Functional groundcovers can be planted at low densities to achieve canopy closure (for example, 400 to 500 mm spacing). However, decorative groundcovers should be planted at higher densities (for example, 150 to 200 mm spacing). For smaller, ephemeral plant species that die back in summer (for example, Wahlenbergia communis), planting density should be increased to 100 to 150 mm spacings, to allow for plant loss and to maintain the sense of massed planting.

                    Designing for easy maintenance

                    ​Good planting design considers maintenance needs. For instance, larger shrubs that require minimal maintenance can be placed in less accessible areas. Species that require similar types of maintenance can be grouped together (‘zoned’) to reduce the frequency and costs of these interventions.

                    Establishment

                    ​Irrigation will be needed during plant establishment, regardless of rainfall expectations. Climate change is leading to less reliability in rainfall; in Melbourne this often includes drier than normal winter and spring periods. 

                    Weed control will also be required during plant establishment. Some native plants can be highly susceptible to common herbicides such as glyphosate and hand weeding may be necessary to prevent inadvertent plant deaths. If maintenance staff or contractors have limited plant identification skills, some plants (particularly young native grasses) may be mis-identified as weeds. In both cases, consider higher maintenance for the first two years after planting to ensure plantings are well established before being transitioned to lower maintenance regimes.

                    Mulches

                    ​In newly planted sites, the use of mulch is often beneficial to reduce weed competition. Generally applied to a depth of 75 mm, the material can be either mineral (for example, aggregate) or organic in origin. Any organic mulch used should comply with AS4454–2012: Composts, soil conditioners and mulches and should be low nutrient and weed free. 

                    Mulches of uniform size and materials such as wood chips are unlikely to provide as many fauna resources as diverse mulches which consist of the leaves and twigs remaining after eucalypt oil distillation, or the chippings from whole tree removal. The latter, more structurally complex mulches, should be preferred. As plantings grow and bare ground reduces, there is less need for mulches. The practice of constantly adding mulch every year can reduce the opportunity for natural recruitment of the planted species, which should be an objective in most sites long-term. Note that the application of mulch if not required for plantings in scoria. 

                    4. Develop a maintenance plan

                    Maintenance is critical and must be considered from the project’s inception. Maintenance and long-term management considerations will influence design and implementation, especially because diverse plantings with a variety of life forms and plant habits are often more costly to maintain than simple groundcovers. For instance, pruning or watering requirements may vary for each species and require more site visits per year.

                    Project planners need to ensure that maintenance staff have adequate skill levels (for example, plant identification skills) – it is easy for seedlings to be mistaken as weeds. More often than not, the workers typically employed by councils to manage standard streetscapes do not have the skillsets or experience required to effectively manage diverse native plantings in urban settings. Budget may be needed for upskilling or training, or for hiring more highly qualified people. 

                    Ecologically sensitive, post-planting maintenance should include: 

                    • Fostering natural recruitment of plantings through weed and pest management practices.
                    • Reducing the frequency of pruning of native plants in order to retain insect habitat.
                    • Spot spraying weeds solely in open areas and edges to avoid off-target damage to sensitive species.
                    • Limiting leaf litter removal to when it is clearly having detrimental effects to existing plants. 

                    Other general maintenance procedures include manual hand weeding, deadheading and seed removal of weeds, rubbish collection, and infill plantings when necessary. 

                    In many streetscape plantings where there is minimal maintenance, to reduce recurrent costs in weed maintenance, plantings should be designed to achieve complete canopy coverage from groundcovers between 24 and 36 months post-planting. In streetscape biodiversity plantings, canopy closure may not be possible in these timeframes and higher recurrent maintenance will be needed to manage weeds long-term.

                    5. Consider using additional habitat features

                    Most urban fauna require resources other than those provided by living vegetation, and standard urban vegetation and landscape management practices can act to 'ecologically sanitise' public landscapes. Public expectations and perceptions of risk often lead to the removal of dead trees, branches and leaf litter, which lead to negative impacts on biodiversity. Developing creative ways to incorporate and retain these resources in streetscapes will enable a greater range of fauna species to colonise and persist in them.

                    Leaf litter

                    ​Maintenance should maximise the retention of leaf litter. A well-developed leaf litter layer will provide significant resources for biodiversity and facilitate important ecosystems process such as decomposition, nutrient cycling and germination, and an increase in the biomass of detritivores (creatures that feed on dead organic matter, especially plant matter), which can be an important food source for insectivorous birds and predatory insects. Heavy falls of leaf litter, for example from deciduous trees in autumn, should be removed because they can smother vegetation and may produce excessive levels of nutrients in the soil. If possible, consider edge design that minimises the loss of leaf litter from beds. 

                    Logs and branches

                    ​Large logs and branches, termed coarse woody debris by ecologists, are rare in urban areas, probably because they are perceived as untidy or dangerous or collected for firewood. Coarse woody debris is beneficial to a range of biodiversity and ecosystem processes in urban areas, for instance: 

                    • Increasing solitary bee and wasp species richness and abundance.
                    • Providing habitat for carabid beetle species that are sensitive to urbanisation and which live in decaying wood.
                    • Capturing and retaining moisture, nutrients, leaf litter and seeds.
                    • Creating microsites for seedling germination.
                    • Providing shelter, nesting, dispersal and forging places for many species, including small vertebrates, such as skinks.

                    Subject to safety considerations, designers should consider placing large logs and branches onto roundabouts, medians and wide nature strips to increase biodiversity habitat and stimulate ecosystem processes. Be aware that there is a risk of theft (for example, for firewood), which may be minimised by locating logs in less accessible areas, or in areas with good surveillance.

                    Rocks

                    ​Consider combining rocks with log and branches in site design. Rocks provide crevices for shelter, habitat and basking sites for a range of species, including small vertebrates, such as skinks. They function similarly to coarse woody debris but do not decompose or get collected as firewood, and they provide warmer basking sites for ectotherms such as invertebrates and reptiles. 

                    Bare ground

                    Most of Australia’s native bees, including flagship species such as the Blue-banded bee, nest in the ground. However, in public landscapes, such as streets, areas of bare ground suitable for bee nests can be rare due the prevalence of impervious surfaces, dense turf, mulch or compacted soil which can prevent bees from nesting. In addition, frequent disturbance by mowing, pedestrian trampling or chemical spraying can collapse any nest holes that may be built. 

                    To encourage ground-nesting bees to construct burrows in streetscape plantings, it is important to include patches of bare (unplanted) soil that will remained undisturbed. It is thought that placing scattered rocks or pebbles over the patch of soil or having it protected from the rain by an overhanging structure will increase its attractiveness to ground nesting bees.

                    Bee hotels

                    ​To replace lost nesting habitat for solitary bees, bee nest boxes, also termed ‘bee hotels’ are being widely encouraged due to their potential benefits. While little research has been conducted to assess their effectiveness, bee hotels are a good community engagement tool and are widely used in Australia. Incorporating a combination of small hollow twigs and specially made mud brick nest blocks into bee hotels can increase nesting habitat for above ground and ground-nesting bees.

                    More information

                    ​Head to Streetscape biodiversity or contact nature@melbourne.vic.gov.au for more information.
                      Was this page helpful?

                      If you'd like to give more feedback or ask a question, please contact us.