AHCPGD301A Implement A Plant Establishment Program

Class Notes

INDEX

ITEMPAGE

How Plants Grow – The Basics3

Some Bits About Soil5

Soil Ameliorants/Additives8

Improving Urban Soils For Plant Growth9

Plants In The Landscape13

Mulches16

Planting Techniques21

Weed Control24

Amount Of Nutrients In Plants30

What Is A Fertiliser?31

Fertiliser Labels32

Problems Faced By Newly Established Plants33

Nutrient Availability pH Chart34
HOW PLANTS GROW - THE BASICS

To understand how to best establish, and care for plants you need to have an understanding of how plants grow.

Most flowering plants have four main parts:

  • Roots In most plants these grow below the soil, although some plants will attach themselves to other objects, such as trees or rocks, and some aquatic plants will have their roots immersed in water.
  • Stems the framework of the plant. In some plants stems are greatly reduced, or virtually absent creating flattened or squat plants.
  • Leaves required for respiration, transpiration and photosynthesis. In some plants, such as succulents, the leaves may be greatly reduced, modified or absent.
  • Reproductive Parts Flowers and fruits.

Roots

Roots absorb nutrients, water and gases from the soil (or other growing medium, such as potting mix, or water), transmitting these "chemicals" to feed other parts of the plant. Roots hold the plant in position and stop it from falling over or blowing away.

Stems

The main stem and it's branches are the framework that support the leaves, flowers and fruits. The leaves, and also green stems, manufacture food via the process known as photosynthesis, which is transported throughout the plant, including the flowers, fruits and roots. The vascular system within the stem consists of canals, or vessels, which transfer nutrients and water upwards and downwards through the plant. This is equivalent to the blood system in animals.

Leaves

The primary function of leaves is photosynthesis, which is a process in which light energy is caught from the sun and stored via a chemical reaction in the form of carbohydrates such as sugars and starch. The energy can then be retrieved and used at a later date if required in a process known as respiration.

Leaves are also the principle plant part involved in the process known as transpiration where water evaporates, mainly through the leaf pores (or stomata), sometimes through the leaf cuticle (or surface) as well, out of the leaf into a drier external environment. This evaporating water helps regulate the temperature of the plant. This process may also operate in the reverse direction whereby water vapour from a humid external environment will pass into the drier leaf.

The process of water evaporating from the leaves is very important in that it creates a water gradient or potential between the upper and lower parts of the plant. As the water evaporates from the plant cells in the leaves then more water is drawn from neighbouring cells to replace the lost water. Water is then drawn into those neighbouring cells from their neighbours and from conducting vessels in the stems. This process continues, eventually drawing water into the roots from the ground until the water gradient has been sufficiently reduced. As the water moves throughout the plant it carries nutrients, hormones, enzymes etc. In effect this passage of water through the plant has a similar effect to a water pump, in this case causing water to be drawn from the ground, through the plant and eventually out into the atmosphere. As much as 95% of the water taken in by a plant is lost to the atmosphere through evaporation from the foliage.

Reproductive Parts

These reproduce by pollen (ie: male parts) fertilizing an egg (ie: female part found in the ovary of a flower). The ovary then grows to produce a fruit and the fertilized egg(s) grow to produce seed.

SOMEBITS ABOUT SOIL

Soil is very important to most plants because:

  • Plants derive many of their nutrients from the soil
  • The soil holds the plant firm and stops it falling over (provides support)
  • The plants’ roots obtain both water and air from soil (or growing media). A soil (or growing media) with too much air content leaves the plant starved for water. A soil containing too much water leaves the plant starved for air.

What Is Soil Made Of?

Soil consists of five main components. These are:

  • Mineral particles, consisting of small particles of various sizes of rocks and other minerals that have been produced from parent rocks by weathering processes. Soil particles range in size from very small (clay) to large (sands & gravels), with silts in the intermediate range.
  • Organic matter (plant and animal remains) in varying states of decomposition.
  • Water, which contains varying amounts of dissolved nutrient elements and other elements or compounds (can include toxic ones). This is known as the 'soil solution'.
  • Air, which fills the space (pores) between the soil particles that are not filled by the soil solution.
  • Living organisms - ranging from massive numbers of microscopic organisms, up to insects, earthworms, and larger animals (e.g. rabbits, wombats).

Why Do Soils Behave Differently?

  • They are made up of varying proportions of the five main components.
  • The main soil components are grouped together in different ways.
  • The parent rocks from which the smaller mineral particles are derived contain a variety of different minerals.
  • The sizes, and relative amounts of different sized mineral particles vary from soil to soil.
  • The different soils have formed under varying combinations of different processes (e.g. length of time, climate, plants growing in them).

Soil Texture

Soil texture is the ratio of sand: silt: clay particles in the soil. Knowing the texture of a particular soil, gives us a good idea of important properties of that soil, such as how well it drains, how well it holds water, how quickly it dries out, and how well it holds nutrients.

There are quite a few different soil textural classes, how many will depend on which texts you refer to. For general horticultural purposes we can classify soils into five main textural types. These are:

TypeProperties

Sand Poor water holding capacity (whc), good aeration, poor nutrient

retention, rapid drainage and drying

Sandy loamIntermediate in properties between sand & loam

LoamGood whc, good aeration, good nutrient retention

Clay loamIntermediate in properties between loam and clay

ClayGood whc, poor aeration, good nutrient

retention but nutrients may be unavailable, poor drainage,

slow drying

Note: In sandy soils there are a high percentage of sand particles, while in clay soils there are a high proportion of clay particles, however, in loams there is a mixture of different sized sand, silt and clay particles (not a high proportion of medium sized particles), hopefully giving it the best properties of each of these.

Comparing Sandy and Clayey Soils

Some comparisons are listed below:

  • Available nutrients are generally low, and retention of added nutrients is poor in sandy soils compared to clayey soils.
  • Sandy soils are structureless, while clayey soils can vary in structure from highly structured (crumbly) to poor (cloddy, massive).
  • Well-structured clayey soils can have good aeration and drainage, however, clayey soils generally have much poorer aeration and drainage compared to sandy soils.
  • Water holding capacities of sandy soils are generally low, while those of clayey soils are high.
  • Clay soils are generally much harder to dig than sandy soils. They can be sticky when wet, and set hard when dry.
  • Sandy soils are quite stable, with little or no movement (shrinking, expanding), while some clay soils can expand and contract extensively according to moisture levels, with cracking quite common in very dry clay soils.
  • Some sandy soils have water repellence (these are known as hydrophobic soils).
  • Compost and slow release fertilisers are generally the most effective for improving fertility of sandy soils – the nutrients are not as quickly leached out.
  • Water penetration (infiltration) into clays is generally slow. Some clays are good for lining dams (e.g. bentonite).
  • Silty loams often set very hard on drying, while some loams turn to powder on drying.
  • Some clay loams form surface crusts on drying that make it hard for seedlings to get through, and reduce water infiltration and aeration.
  • Clays are easily compacted by traffic. Sands are much less likely to compact.
  • Texture can be changed. A lot of sand is required to "improve" a clay soil. A lot less clay is required to "improve" a sandy soil.

Determining Soil Texture Types

The soil textural type can be roughly determined using a simple feel test as outlined below:

Take an amount of the soil to be tested that will fit comfortably in the palm of your hand. Moisten the soil, by adding water slowly till it reaches a point where it just doesn’t stick to your hand. Then press the soil into a ribbon between your thumb and index finger. Keep making the ribbon until it breaks under its own weight (taking note of the length of ribbon you achieved). Use the following guide to give an indication of the soil’s texture.

Sand-no ribbon, gritty feel

Sandy loam-ribbons to 15 – 25mm, sand grains can be seen and felt

Loam-ribbons to 25mm, no obvious sandiness or silky feel

Clay loam-ribbons to 50mm, spongy, smooth and plastic (may be occasional

gritty bit)

Clay-ribbons > 5omm, smooth and plastic (like plasticine)

References: Gardening Down Under by K. Handreck, Growing Media for Ornamental Plants & Turf by Handreck & Black, and A Student Handbook For The Study of Soils & Growing Media (3rd edn) by Rod McMillan.

SOIL AMELIORANTS/ADDITIVES

Lime

To raise soil pH. Lime will also help improve the structure of clay soils.

  • 1 Kg of lime dug into sandy soil to a depth of 15cm over 10sqm. will raise pH from 4.5 to 5.5.
  • In loam soils about 2.2kg is needed to do the same.
  • In clay about 4kg is needed to do the same.
  • Lime can be obtained for around $5 per 25kg bag (cheaper in bulk).

Gypsum (CaS04)

Used to help improve the structure of clayish soils, without altering the pH to any great degree.

  • Generally added at the rate of 0.5 to 1kg per square metre of area to be treated.
  • Gypsum can be obtained from garden supply companies for around $5 to $6 per 40kg bag. It is much cheaper when bought in bulk (e.g. trailer load).

Sulphates (sulphur containing salts)/Sulphur powder

Used to help lower soil pH.

  • 0.7kg of powdered sulphur cultivated over 10sqm. to a depth of 20cm in sandy soil will lower pH from 7.5 to 7.
  • In loam about 2kg of sulphur is needed to do the same.
  • Sulphur is expensive, and so it is generally only practicable to use it to treat small areas. It can be obtained for about $4 to $5 per 0.5kg.

Peat Moss

This can be used to acidify small areas. One cubic metre of peat has about the same effect as 600g of sulphur. Peat is very expensive, but has the added advantages of adding organic matter to the soil. A cheaper, renewable material made from the husks of coconuts (and sold in Australia as ‘Copra Peat’ by Debco) can be used as a peat substitute.

Wetting agents

Used too improve the wettability of soil (e.g. water penetration), particularly of non-wetting sands, and potting mixes with large amounts of organic materials as components. A wetting agent is commonly a type of detergent that is slow to break down, and that isn't toxic to plants at the recommended rates. The wetting agent helps break down the surface tension of water allowing it to spread more easily across the surface of soil and potting mix particles. Good quality wetting agents will last at least eight months. Kevin Handreck in an article in Australian Horticulture Magazine recommended, Chemtech Aqua Soil Wetter, Wetta Soil, and Saturaid Granules (Debco).

IMPROVING URBAN SOILS FOR PLANT GROWTH

The majority of Australia’s human population lives in urban areas. The Sydney & Melbourne greater metropolitan areas alone, between them, contain a population approaching 8 million people. While some soils in urban areas may be naturally poor for plant growth (e.g. shallow, low fertility, poor structure), many urban soils have been heavily modified, in particular during construction for commercial and domestic purposes, and in recreation areas due to heavy use. What you do to improve urban soils for plant growth will depend on how much time, effort & resources (materials, equipment, money) you are prepared to invest.

Common Problems With Urban Soils

PROBLEM

/

POSSIBLE SOLUTIONS

(in no particular order)
Naturally occurring shallow top soils (poorly structured subsoil or bedrock close to the surface), often resulting in restricted root growth (poor plant growth, poor anchorage), and poor drainage /
  1. Import top soil from elsewhere (see Footnote 1)
  2. Where depth of subsoil is sufficient deep rip to open up soil, and embark on a soil improvement program (e.g. soil ameliorants such as lime or gypsum, addition of organic matter, and sub-surface drainage systems)
  3. Where subsoil is also shallow no-dig gardens may be tried, or use of plants capable of establishing and surviving such conditions – these may be permanent plantings, or used as colonisers to improve conditions for later plantings

Top soil has been removed (e.g. during house excavations) generally leaving subsoil, or where deeper excavation has occurred, bedrock. / (see naturally occurring top soils – above)
Subsoil from excavations dumped/spread over existing topsoil in adjacent areas /
  1. Remove subsoil where possible – this might be used as fill elsewhere. In particular remove such soil that might overlie the roots of established trees and large shrubs.
  2. If the depth of over-lying subsoil is fairly shallow it may be easier to either leave it, or incorporate it in to the underlying pre-existing topsoil. Soil improvement programs can also be carried out at this time (e.g. add lime or gypsum, add organic matter, etc.)

Disturbed or mixed soil – varying in characteristics /
  1. Add organic matter, add gypsum and/or lime if required, and mix well. Do not bring subsoil to the surface.

Compacted soils as a result of construction activities, or heavy foot and/or vehicle traffic.
Compaction reduces the movement of air and water into and through the soil, makes it harder for plant roots to penetrate through the soil, and hence has a significant impact on plant growth, and microorganism activity.
Large areas of compacted soils can also lead to increased surface runoff of water, that can lead to increased flooding, increased erosion, particularly during construction activities, and increased pollution of waterways. /
  1. Where possible protect the soil to prevent further compaction (see below)
  2. Reduce the compaction by such methods as: cultivation (see Footnote 2), incorporation of lime and/or gypsum (see Footnote 3), incorporation of organic matter, or preferably a combination of these methods
  3. Annual aeration of turfed areas (e.g. coring).
  4. Modifying irrigation regimes to prevent surface runoff – frequent light applications of water may be required until compaction is reduced.

High water tables, or waterlogged soils – this may be ongoing or seasonal /
  1. If due to the presence of impermeable sub-surface layer, then break through layer (e.g. deep tilling or ripping), or install sub-surface drainage.
  2. Create mounds or raised beds to improve drainage for plants.
  3. Choose plants that will cope with the conditions.
  4. Careful management of irrigation regime to avoid excess watering that may help increase the problem.
  5. If possible reduce/divert water causing the problem.

Hydrophobic soils – these are soils, which when dry, can be difficult to rewet. This can be common with some fine sandy soils. /
  1. Use wetting agents, such as Saturaid, to improve water infiltration into the soil, and retention in the soil.
  2. Keep the soil moist – don’t allow it to dry out.
  3. Mulch the soil to help keep it moist, and to reduce surface runoff.

Soil erosion /
  1. Reduce slopes (e.g. terracing)
  2. Manage irrigation effectively to minimize surface runoff.
  3. Mulch, or provide some other form of protective barrier
  4. Use plants that effectively bind the soil.

Soil crusting /
  1. Do not leave the soil bare, always provide some sort of protective covering
  2. Add organic matter & mulch
  3. Reduce traffic
  4. Reduce droplet size from irrigation systems

Poor soil permeability & water infiltration /
  1. Add organic matter
  2. Deep rip or till
  3. Mulch
  4. Adjust irrigation rates to achieve maximum infiltration without surface runoff.

Acid soils /
  1. Add lime
  2. Use plants that are adapted to low pH conditions

Alkaline soils /
  1. Add organic matter
  2. Add sulfur and acidifying fertilizers, such as Ammonium sulphate
  3. Use plants that are adapted to high pH conditions

Salt affected soils /
  1. Use salt tolerant plant species
  2. Add organic matter
  3. Add gypsum to displace salts
  4. Leach salts from the soil if water table is not too high by watering heavily
  5. Use water for irrigation that is low in salts

Chemically polluted soils /
  1. Seek advice from appropriate authorities (e.g. EPA)

Footnotes:

  1. Imported topsoil should only be used if it meets with the requirements of Australian Standard AS4419-1998. Problems associated with imported topsoil include the potential for the spread of weeds, pests & diseases; polluted soil, the presence of rubbish/debris, and high salt levels. Imported topsoil must be carefully incorporated into the existing soil to reduce the likelihood of layering occurring. One method is to place one third of the imported soil onto the existing soil, incorporating it in to the top 10cm or so of the existing soil, then adding another third of the topsoil and incorporating it into the top 10cm or so of the previously mixed soil, then add the final third of the topsoil, and repeat the process.
  2. Cultivation should ideally be done when the soil has been thoroughly watered, and then allowed to drain freely for two to three days The soil will then be at or near what is known as Field Capacity. At this stage the soil is generally easier to work than when dry, and will cause less damage to the soil’s structure than when either dry or very wet.
  3. Lime and gypsum are both used to help improve soil structure (break up into crumbs) in clay soils. Not all clay soils will respond to this treatment. A simple test (see attached photocopies) can be used to test whether lime and/or gypsum addition will have any effect. Lime will also raise soil pH, however, gypsum generally has little effect on pH. Application rates generally fit into the range of 0.5-1kg per square metre.

Preventing Soil Damage During Construction Works

Ways to reduce damage to urban soils during construction activities include: