Tree Logic Arboricultural Consultants » Drought solutions

Healthy soil, potential breakthrough research

Stephen Frank — Mon, 05 Jul 2010 05:44:15 +0000

Healthy soil differs from dirt in the myriad of life forms it contains. Soil organisms (the biological properties of a soil) aerate, decompose plant material, assist nutrient absorption, build soil structure, reduce water requirements and play a vital role in the nitrogen cycle.
A proper balance of nutrients and pH obviously play a significant role in healthy plant growth. Biological activity can also affect the pH of the soil and subsequent impacts on the utilisation of of nutrients.
The biological properties of a soil decompose the organic matter in the form of litter falling on the soil surface and subsequently incorporates it into the soil profile. Nutrients are released as by-products, including the mineralization of nitrogen and nitrogen fixation (making nitrogen available to plants). The soil’s physical properties, including moisture content, temperature, aeration (bulk density) pH and nutrient content are necessary for a diverse soil organism population and a high level of activity. Limiting any of these factors limits soil organism activity, organic matter cycling and subsequently reduces soil fertility.
The undisturbed forest soil has organic layers in it’s profile. These organic layers comprise leaf litter at the surface, a decomposition layer and a humus layer. These large, high-molecular-weight molecules are made up of carbon, nitrogen, soil minerals and soil aggregates. The resultant humus is a stable, inseparable part of the soil matrix that can remain intact for hundreds of years.
When OM is incorporated into the surface soil it forms the topsoil (A horizon) and this horizon has the most optimum conditions for plant growth.
Urban soils are generally highly disturbed soil environments that do not mimic the soil conditions of natural forest soils. Human activity is the predominant agent in the formation of urban soils. Urbanisation also contributes unique amendments and contaminants to the urban soil.
Disturbing soil profiles, mixing and filling, and contamination lead to variability. This can also lead to compaction; restricted aeration and water drainage, crusting and bare, often hydrophobic surfaces. Importantly, interrupted nutrient cycling and modified soil organism activity result in unhealthy (low vigour) growth and predisposes plants to other environmental and biological stresses.
Tree decline is as a result of several interacting factors, such as prolonged drought, competition with adjacent trees, pest and disease infestation and generally depleted soil environments. Poor soil structure is a significant predisposing stress factor for plants. Poor soil structure affects water infiltration and permeability, water holding capacity, aeration status and loss of pore space. If plants do not have access to sufficient water and oxygen they will decline.
Healthy soil requires organic matter (OM); it aids in aggregation (soil structure), cation exchange (storehouse of nutrients) and water holding capacity. But most importantly, it sustains biological life in the soil; the greater amount and diversity of biological life there is in a soil the greater potential for healthier plant growth. Soil health is the basis for plant health and by extension, healthy plants can help develop healthy humans.
Tree Logic has commenced a trial to incorporate humus into urban soils. Ninety established Plane (Platanus spp.) street trees exhibiting decline symptoms, were treated using liquid humus, Seasol® and urea. A number of trees in parks and reserves within an eastern Melbourne municipality were also treated.
A sample of the trees to be treated along with controls in close proximity that included healthy Planes and Planes displaying similar malaise were established prior to the commencement of treatments. The samples looked at current season shoot tip extension and leaf size. In addition, leaf samples were fluoresced and data captured on short and long term stress indicators. This data will be compared against future samples to determine the efficacy of the treatments over a 2 year period.
Injecting liquid humus into urban soils will start to build up the organic content of the soils which will aid water holding capacity, cation exchange capacity, and reduce leaching. Organic matter can also buffer effects of any pesticides and stabilise pH. Treatments are carried out in autumn and spring (before bud burst). Humified carbon differs physically, chemically and biologically from the labile pool of organic carbon that typically forms in agricultural soils. Labile organic carbon arises principally from biomass inputs (such as leaf litter) which are readily decomposed.
In conjunction with the liquid humus the soils can also be injected with liquid nitrogen. In degraded urban soils the major nutritional limitation on plant growth is lack of nitrogen (Pulford, 1991). Without an adequate pool of organic nitrogen, which microbial activity breaks down into forms (NH4+ & NO3-), mineral nitrogen is quickly depleted in soils and nitrogen deficiencies develop. Low organic matter content is typical of urban soils consequently nitrogen is the nutrient most limiting to growth (Roberts, Jackson, Smith, 2006).
The other consideration is the on-going nature of the applications, that is, to be successful a number of applications will be required. Products, application timing and rates and costs could be developed upon request.

Porous Paving

Stephen Frank — Tue, 10 Mar 2009 23:52:38 +0000

Hard paved surfaces such as roads, car parks, driveways, and courtyards cover a significant proportion of urban areas. Impervious paving increases peak and total storm water discharge increasing demand on existing stormwater infrastructure and increases downstream flooding. Rapid discharge of storm water deteriorates stream habitat through bank erosion, while runoff from impervious surfaces carry pollutants that reduce water quality. Moreover, impervious surfaces prevent groundwater recharge necessary for the development of healthy trees.

Water sensitive urban design (WSUD), aimed at sustainable solutions to water management and broader environmental protection is gaining global momentum in contemporary urban planning. One WSUD strategy is to reduce impervious surfaces. The use of porous pavement provides an innovative method for achieving several WSUD objectives.

Porous paving is widely employed in the UK and northern Europe, where its use was principally as a flood mitigation technique to minimise the high cost associated with locking up expensive real estate as retention ponds and soaks. Porous paving is increasing in popularity in the United States where its use is being driven in part by the Environmental Protection Agencies (EPA) control on storm water pollution management.

In Australia, the driest continent in the world, there has traditionally been reluctance from government and urban planners to adopt this technology, despite its water management advantages. The adoption of WSUD objectives in Australian urban planning in recent years has provided an opportunity to expand the use of and improve this technology.

Porous paving can be separated into the main product types listed in Table 1 below.

Table 1: Main porous paving product types

Unlike impervious paving, porous paving is designed to allow water and air to flow through the pavement section, and depending on design, may allow infiltration and gaseous exchange into the underlying soil. Infiltration is determined by the rate at which the entire pavement including the base course and sub-base section can absorb, retain and drain water.

In flow through systems where the water is discharged into the natural underlying soil, soil properties will determine the suitability of and influence the design of the paving. Adequate hydraulic conductivity and the ability of the soil to maintain structure and load bearing capacity when wet are integral to the design and therefore success of the paving.

Contrary to common perceptions the structural capacity of some porous pavers extends beyond light load, low traffic areas such as driveways pedestrian paths, courtyards and small car parks. Modular block pavers, and in particular open jointed pavers have proven application in residential streets, commercial traffic zones such as bus terminals and even sites that experience regular heavy industrial traffic including several major shipping port container yards.

Porous pavement is gaining attention for its pollution control properties, having filtration capabilities to remove suspended solids thus improving water quality. Mostly, these pollutants are held in the jointing material or trapped in filtering layers in the base course or sub-base. Over time infiltration rates can be reduced and allowances for this should be made in the design stage.

The functionality of porous paving can be further reduced as oil, grease, fine solids and organic matter become trapped, clogging the system and necessitating the need for cleaning maintenance. Site design considerations that can reduce clogging include the installation of sediment traps, filter strips or gutter systems that pretreat stormwater to remove gross pollutants and sediment. Where paving is likely to receive large quantities of sediment and debris that cannot be controlled, installation should be avoided.

Generally porous pavement systems that rely on achieving porosity through open joints and cells are easier to maintain than porous asphalt, concrete or modular porous paving, which have finer voids that tend to clog more easily. Restoring infiltration capacity of open jointed and celled systems can be achieved by removing and replacing the top layer or drainage material. Cleaning porous asphalt, concrete or modular porous paving requires regular vacuuming or high pressure cleaning to maintain an acceptable level of porosity. Therefore, site design that avoids or minimises the accumulation of sediments over the paving and cleaning and maintenance are integral elements of any permeable paving system.

The benefit to trees of porous paving lies in its ability to provide a healthy rooting habitat, contributing to tree longevity. Trees bring to the urban landscape enormous social, functional and environmental benefits. Trees provide an intrinsic amenity through their ability to moderate the urban heat island effect, improve air quality, reduce glare, attenuate noise, bring a sense of scale to and compliment architecture. Trees have the capacity to contribute to mental and psychological well-being, add economic value to property and encourage patronage to commercial districts. Consequently, the importance and public veneration of trees in the urban forest is increasing.

The level of benefit a tree provides is commensurate with longevity and ultimate size. Many urban tree planting sites occur on compacted soils within or surrounded by impervious paving that present trees with hostile growing environment where ground water recharge is limited and gaseous exchange poor. Subsequently, many urban trees develop diminutive stature, are easily drought stressed and susceptible to pest and disease, ultimately limiting their potential lifespan.

Conversely, porous paving that allows moisture infiltration and gaseous exchange to the underlying soil, provides an improved rooting environment similar to a natural soil surface. In combination with other “tree friendly” technologies such as load bearing rooting media or “structural; soils”, providing modified growing environments that includes the application of porous pavement systems will allow more successful urban landscapes to be developed; a landscape in which increased opportunities for tree planting are provided.

No single porous pavement system has universal application and careful selection of the appropriate pavement material is required to achieve the design intent, functionality and cost effectiveness for a project. The uptake of WSUD in Australia has created an opportunity for the increased use of porous paving that will add to current knowledge influencing future developments and improvements in this useful technology that could also facilitate the increased presence of healthy long lived trees in cities.

Heat combined with water stress, Autumn comes early…

Stephen Frank — Tue, 10 Mar 2009 22:22:30 +0000

Heat stress
According to Kozlowski, Kramer & Pallardy (1991) the thermal death point of most active plant cells varies from 50 to 65C. This is dependent on species, age of tissue and duration of exposure to high temperature. However, high temperatures below the thermal death point can often damage woody plants. Symptoms of this type of damage include scorching of leaves and fruits, abscission of leaves, sun scald or burn to bark and growth inhibition.

Often the temperatures of the surfaces adjacent to trees can exceed 65C, for example radiated heat from road surfaces, which create high evaporative potential.

The symptoms of heat stress are often interrelated or similar to those caused by water stress.
The mechanism of heat injury can be complex, however during January and early February 2009 Melbourne’s trees experienced direct ‘heat shock’ injury, this followed extended periods of excessively high ambient air and radiated temperatures, in combination with existing dehydrated plant conditions. Plants are often injured by dehydration associated with high transpiration rates caused by high temperatures and low relative humidity.

Photographs above show the effects of high heat and water stress over one week in January 2009 on a London Plane (Platanus x acerifolia) located in Melbourne’s eastern suburbs.

What lead to the rapid defoliation of many trees in Melbourne was a combination of high temperatures and hot, dry winds. Wind burnt leaves first wilt then dehydrate rapidly becoming brittle within a day and dependent on degree of dehydration and period of high temperatures, can be shed within a few days (Kozlowski, Kramer & Pallardy, 1991).

Melbourne’s trees were already experiencing water stress with low soil moisture levels and water absorption not matching water loss through transpiration.

Water stress

Water stress is usually attributable to drought, however it develops whenever water loss exceeds absorption long enough to cause a decrease in plant water content and sufficient loss Photographs on left show the effects of high heat and water stress over one week in January 2009 on a London Plane (Platanus x acerifolia) located in Melbourne’s eastern suburbs. of turgor, which causes a decrease in cell enlargement and disturbance of various essential physiological processes.

The plant water balance is analogous to a bank balance that relies on a series of deposits and withdrawals. Therefore, either rapid transpiration (excessive withdrawals) or slow absorption (inadequate deposits) can cause plant water stress. In hot, dry weather it can be a combination of the two.

In moist soil, water absorption is controlled largely by the rate of transpiration, but in drying soil it is gradually reduced by the decreasing difference in water potential between roots and soil and the increasing resistance to water movement toward roots through drying soil.

Plant tissues become dehydrated with the initial response of wilting leaves and shoots (loss of turgor) (Costello, et al., 2003). Strong, hot winds can exacerbate water deficits and increase plant water loss by up to 30% (Costello, et al., 2003).

If water loss is severe, leaves develop marginal scorching leading to further necrosis and premature leaf senescence and leaf shedding, either by early abscission or withering. Leaf shedding could be seen as a beneficial adaptation that reduces water stress.

Plant adaptation to water stress

Plants have evolved as a result of morphological and physiological adjustments that suit their native habitats and facilitate survival of moisture stress. In general terms, droughts are avoided or tolerated to various degrees by plants with the help of structural or physiological adaptations that postpone dehydration or that enable plants to tolerate dehydration without serious injury.

Drought avoiders/evaders are generally annuals that complete their life cycles within a few weeks after seasonal rains. Evaders can also consist of perennial herbs and bulbous species, which die down or dormant during hot dry periods. They can also consist of seed banks or vegetative perennating organs.

Drought avoidance does not generally apply to trees as they are long-term components of the landscape and cannot ‘avoid’ drought conditions. There are some woody species that can exhibit this strategy, for example summer deciduous trees, such as Jacaranda.

The most important type of drought tolerance involves postponement of dehydration by effective root systems, very efficient water transport systems, control of water loss, or a combination of all three.

A good safeguard against drought injury is a deep, extensively branched root system that can absorb moisture from a large volume of soil. In times of low rainfall soils generally dry from the surface down due to evaporation and shallow root systems of plants. Therefore shallow rooted plants suffer water stress earlier than deep-rooted ones. One role of mycorrhizae may include the improvement of water absorption as well as nutrients and therefore improve drought tolerance. Large root systems are important for seedling establishment. However large root systems are not always desirable in horticultural activities, for example photosynthate is channelled away from stem and fruit production, and excessive root systems can cause damage in urban areas.

Some plants have developed mechanisms to control of transpiration. These generally comprise species that have evolved in environments where drought stress is a regular occurrence. Morphological and physiological characteristics include the development of thick, heavily cutinised, sclerophyllous leaves with low cuticular transpiration and stomata that close promptly in dry air or when leaves are water stressed. Low cuticular transpiration is probably more a result of the thickness of the wax deposited on it rather than the thickness of the cuticle. Accumulation of wax in stomatal antechambers is particularly effective. Stomatal response to water stress is more important than the number and size of them. The leaf surface exposed to radiation can be reduced by changes in orientation and angle of exposure, which is the case for many eucalypts. Leaf shedding as discussed earlier aids in decreasing water loss.

Anti-transpirants are used to reduce transpiration, either by causing closure of stomata or by coating the foliage with a film that is more or less impermeable to water.

Water storage is another way of postponing dehydration. The use of stored water to replace that lost through transpiration can supply from one-third to several days of water requirement dependent on the species. Water is stored in sapwood and to a lesser extent in bark. Water storage is an important characteristic for cacti and succulents.

Dehydration tolerance is the final step in the ability for plants to avoid desiccation and death. Different species have different dehydration tolerances, for example resurrection plants such as the genus Selaginella, which are of less importance in horticultural practices compared to postponement of dehydration.

These strategies have developed in species within their natural distribution and research into application within horticulture is very thin.

Plants can sometimes build up tolerances to heat with specific proteins called ‘heat shock’ proteins. These proteins can protect certain cell components and enzymes from inactivation (Kozlowski, Kramer & Pallardy, 1991). Some genus like Eucalyptus and Quercus can have species with both conserver and tolerator characteristics.

All species, irrespective of inherent moisture-stress tolerance, are most sensitive in the first months after transplanting in the landscape, and secondly, in the maturity to senescence phases of their life cycle.

In the first case, it is primarily due to the shoot: root ratio resulting from nursery production methods. Mature or senescent plants present a problem of size and the plants ability to supply water to its most distal parts. Furthermore as woody plants grow there is a greater percentage of non-photosynthetic parts. This reduces photosynthate (carbohydrates) that assists in osmotic adjustment and other physiological processes, including root growth.

Success in the urban landscape will be dependent on the soil moisture content and climate of the particular area and the species ability to tolerate pervading climatic conditions.

References:

Costello, L. R., Perry, E. J., Matheny, N. P., Henry, J. M. & Geisel P. M. (2003) Abiotic disorders of landscape plants. A diagnostic guide. University of California. Agriculture and Natural Resources. Publication 3420. Kozlowski, T. T., Kramer, P. J. & Pallardy, S. G. (1991) The physiological ecology of woody plants. Academic Press.

Water Management of Mature Street Trees

Stephen Frank — Tue, 09 Dec 2008 04:41:36 +0000

by Ian Shears.
Senior Tree Planner. City of Melbourne

City of Melbourne Experience

The City of Melbourne is internationally recognised for its tree-lined boulevards, parks and gardens. Trees beautify, define and soften landscapes and give scale to buildings in addition to providing shade and wildlife habitat. Trees are the most life enriching of all the types of vegetation used in the urban environment. They also contribute significantly to the maintenance of a healthy urban environment by trapping airborne pollutants and absorbing carbon dioxide.

The City of Melbourne manages approximately 60,000 trees including approximately 18,000 street trees. Using the City’s ‘tree amenity valuation formula’ the total value of Melbourne’s trees is estimated to be over $600 million. This asset is irreplaceable in the short term and the tree population requires close monitoring and management to ensure its continued good health. Street trees also increase values of adjoining properties.

Melbourne has some of the most significant stands of mature elm trees remaining in the world following the destruction of many of the elm populations in the Northern Hemisphere by Dutch Elm Disease. The elms lining the major boulevards of Victoria Parade and Royal Parade, along with the avenues of trees in the Fitzroy Gardens are registered as significant by the National Trust.

Of the City’s tree stock approximately 15,000 trees have grown in turf areas with regular irrigation. These include park trees and those grown in turf medians such as Royal Parade. Irrigation systems in the past have generally been designed to water the park surface, median or nature strip grass using manual or automatic surface sprinklers. Although this method of watering keeps the grass green it is not efficient in watering trees as it encourages them to develop surface root systems. Regardless of the species of trees and because of historical horticultural practices and the perception that water is a limitless commodity, trees have become dependent on regular surface watering and are less drought tolerant. Many of the trees in the City of Melbourne have been stressed over recent years as a result of low soil moisture.

The severity of the problem has increased over the last couple of years. There are a number of factors that have contributed to this situation. Reduced rainfall in recent years with Melbourne experiencing 10 years of drought. Reduced application of supplementary water through changes to irrigation management initiated by water restrictions. Reduced uptake of rainfall through increased hydrophobicity of soils.

In response to the drought and a move away from using turf sprays to irrigate trees the City of Melbourne has used a range of alternative ways to deliver water effectively to tree root systems and maintain soil moisture at levels to maintain trees in a healthy condition.

Soil moisture readings are taken in the City’s main gardens and boulevards in order to inform water application by monitoring the available water for the trees. The City’s irrigation systems are being changed in order to ensure that the trees are provided with adequate water.

In a major move away from turf sprays over 160km of sub-surface drip line has been installed. These systems are hooked up to existing infrastructure. A fleet of water tankers and water-filled barriers have been brought in to supply water to drought stressed trees that cannot be adequately watered using the irrigation systems. The water tankers are taking reclaimed water from the Royal Park Wetlands.

Recycled mulch has been placed under a large number of trees in parks that may be more susceptible to the dry conditions.

The sub-surface drip lines are considered to be a temporary measure and a more permanent and robust system has been developed to deliver water efficiently in a sustainable way. Street trees present particular challenges in terms of irrigation. These challenges include:

Tree roots contained within median and street structures – limited water storage volume and limited catchment opportunity
Tree root distribution highly variable and non symmetrical
Access to root systems often limited by hard surfaces
Tree roots in competition with turf roots for irrigation water
Significant roots located deep within the soil profile – water needs to be delivered at depth
Canopy interception of rainfall can be significant
Compacted soils (low infiltration rates) – particularly on nature strips
High peak daily water requirement
Street trees are often high traffic and high maintenance areas
Root disturbance and damage e.g. excavation reduce the effectiveness of parts of tree root systems
The street trees may already be stressed due to disease or damage

A key consideration for the future watering of the trees will be the development of tree watering systems that will be permanently installed and supplied from a sustainable water source.

The following criteria were developed to establish the context within which a suitable tree watering technique could be identified.

Irrigation water effectively delivered to the tree root soil volume so that healthy growth can be maintained. Watering throughout the depth of the soil profile and lateral distribution are required.

No overflow or surface flooding
Minimum damage to existing roots through installation
Installation technique not to impede root development
Technique to work effectively in a range of soil types
Plumbing of water delivery to allow regulated, low flow rate, delivery with minimum risk of blockage
Installation technique to be flexible should large roots, services and/or rocks be encountered
Installed technique to allow ground footprint area to be safely trafficked and not subject to subsidence. It should withstand loading that is expected from maintenance machinery and vehicles including trucks
Robust construction of water delivery system
Water delivery hardware to be accessible and protected using appropriate valve box and secure cover
Technique to remain functional, without need for major restoration works, for a period of ten years
Installation to be environmentally sensitive and responsible e.g. not waste water, any soil waste used responsibly
Technique can be readily and safely installed and cost effective
Water delivery program to be able to be accommodated within existing irrigation scheduling capability
Technique to be repairable should tree root and soil conditions interfere with the functioning of the system.

The City of Melbourne decided, in early 2007, to investigate watering techniques that could be used to maintain trees, located in high profile streets and boulevards, in a healthy condition. The trial investigated a range of drip watering and tree watering well products. Restricted root systems, highly variable soils, high traffic and high exposure characterize these trees.

The trial was carried out in Royal Parade, Parkville, where elm trees are positioned in both medians and nature strip areas. The medians are typically raised concrete structures, approximately 500 mm high and 4 metres wide.

A range of water well products and a watering trench were trialled with the watering trench found to perform best.

The key evaluation criteria included the (a) distribution of water (vertical and lateral), (b) presence of overflow and (c) installation requirements.

The trench was considered to potentially have the advantage of providing a wider distribution of water, allow a relatively large volume of water to be delivered rapidly and, if necessary, allow grass to be grown over the surface.

The basic dimensions of the trench was approximately 1.2 metres long, 300 mm wide and 300 mm deep. The total volume of the trench cavity is approximately 110 litres. Both sand and graded gravel (7 mm), referred to as quarter minus, was used as the trench medium.

The trench version which performed best consisted of quarter minus gravel. The quarter minus provided ample void water space for water storage (approximately 30%) was stable when saturated. The washed sand material was found to become soggy or slushy and provided virtually no top loading support. This is an important consideration for a watering system in these areas is that that present no undue risk to the public.

Water distribution from the trench was found to be variable however typically in the range of 500 mm laterally, beyond the edge of the trench, at a depth of 500 mm.

The water jet technique was considered to be the most effective in terms of constructing this type of trench. However the watering jet technique is potentially expensive and requires considerable support in terms of roadway traffic management restrictions to accommodate the truck. The trench watering system has been installed in the majority of Royal Parade, sections of St Kilda Road and in sections of Birrarung Marr

The change to sub-surface delivery of water has improved the health of trees. Generally trees have taken one summer season to adapt to the new source of water and by the following summer are displaying greater health with fuller canopies and minimal indications of drought stress.

Click to download printable pdf

Carbohydrate and Surfactant Treatments

Stephen Frank — Fri, 12 Sep 2008 07:34:25 +0000

Recently published research in the application of carbohydrates (sucrose) in root drenches has shown considerable promise in improving general plant health whilst limiting the effects of environmental stresses and even herbicide damage. Peer reviewed and published research on field trials conducted on containerised plants, young transplanted and established mature trees demonstrated that carbohydrate treatments applied at specific rates resulted in a decrease in time taken for the initiation of new roots, an increase in the number of roots initiated and improved root elongation rates.
More traditional forms of soil improvement treatments generally contain macro and micronutrients and encourage beneficial microbial activity which in turn helps release nutrients in the soil for plant uptake. These assimilates are then transported to the crown of the plant and used in the photosynthetic process to generate carbohydrates required for root growth. By providing sucrose at specific rates in and around the root zone of the plant, the carbohydrates required for root growth are immediately available thus limiting the plants reliance on the crown to provide these assimilates. This can be particularly useful in circumstances where the plants crown may have decreased foliage levels, small and/or chlorotic leaves and which may not have the capacity to produce sufficient carbohydrates for root growth.
Carbohydrates are also known to stimulate beneficial soil microbial and fungal rhizosphere that assist in plant nutrient uptake. In addition, the use of surfactants in carbohydrate drenches can improve irrigation performance and reduce water requirements. Surfactants aid in the wetting and movement of water in media and landscape soils. These are biodegradable detergent-like products that work by lowering the surface tension of water so that wetting is uniform and effective. If media wetting is not uniform, irrigation water tends to move through the larger pores in the media where it is subject to downward gravitational forces. This in turn leads to increase leaching and reduced irrigation efficiency. By improving penetration, wetting, and water movement, media surfactants can increase the effective wetting area thereby increasing irrigation efficiency.
Carbohydrate and surfactant drenches are applied through soil injection techniques that deliver the material at a depth of approximately 150 – 200mm. This is done to reduce the loss of material through natural evaporation and to better target the root system of the subject plant. Treatments shallower than this could result in other plants (particularly turf) drawing up the sucrose before the target plant has a chance to absorb it.
Click to download printable pdf

Fertilising Trees

Stephen Frank — Tue, 11 Mar 2008 02:51:47 +0000

Fertilising trees refers to the practice of adding supplemental nutrients (chemical elements) required for normal growth and development.
You can’t ” feed” a tree, since trees produce their own sugar via photosynthesis, for which they use nutrients as part of the process.
A reasonably fertile soil will have enough nutrients to satisfy the requirements of growth on most established trees. Trees adjust their growth and development rates to the level of nutrients present in the soil, and will usually grow vigourously as long as the roots can continue to grow.
In nature, trees get nutrients from air, recycled organic matter, beneficial microbes, and soil minerals. In urban settings, the recycling of organic matter is often reduced, beneficial microbes may be minimal, and some minerals can be unavailable be- cause of the soil pH.
Lack of water and organic matter, and soil compaction often limit growth of urban trees much more than nutrient levels.
Infertile soils are most common in new building areas, both commercial and residential, where the ‘natural’ soil has been altered. Altered soils display poor physical and chemical properties for tree and shrub growth. Soil modifications, where required, along with proper fertilisation may improve nutrient uptake of plants.
Fertilising a tree can improve growth; however, if fertiliser is not applied wisely, it may adversely affect the tree. Mature trees making satisfactory growth may not require fertilisation.
Adding fertiliser, especially nitrogen, around stressed or root damaged trees can be harmful unless you have determined that the stress is due to nutrient deficiency.
Harm can occur when a tree in decline with low energy reserves attempts to incorporate nitrogen into cell components.
Since this process requires energy expenditure, reserves can be lowered further. This could lead to a further decline in health as trees with low energy reserves have reduced ability to deal with the effects of injury and pests.

Click to download the fact sheet pdf

Mulch for trees

Stephen Frank — Thu, 01 Mar 2007 22:58:47 +0000

Peoples awareness of the potential benefits to gardens of using mulch has increased markedly over the past few decades. With the recent limitations imposed on domestic water resources and the implications for water use in the garden, plant moisture stress caused by drought is becoming an increased cause of tree decline. Mulch is gaining attention as one strategy that can assist gardens to cope with hot dry conditions.
Mulch is a covering placed over the ground. Numerous materials are used as mulch and these can be broadly divided into organic products, such as wood and bark chips, shredded leaf and branch matter, recycled pallets, leaf litter, saw dust, and straw, and inorganic products, such as crushed rock, gravel, plastic, and shredded rubber to name a few. Organic wood based mulch is the focus of this article.

Download full fact sheet as printable pdf

Watering mature trees

Stephen Frank — Fri, 27 Oct 2006 12:48:12 +0000

Mature trees can have large water requirements and may lose up to hundreds of litres of water daily through their leaves, especially in hot and/or windy weather. Trees will experience stress if insufficient soil water is available for use by the tree to replace the water lost through the leaves. Continued stress can lead to serious problems for your trees. Supplementary watering when required can assist in maintaining your treeâ€™s health.
Landscape trees commonly grown in Australia originate from many different climate zones and have different water needs. Knowing what trees you have and what their water requirements are will help you understand their watering needs. If in doubt, hire a knowledgeable, certified arborist for advice.

Download full fact sheet as printable pdf