Gardening

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The weather is getting warmer, and gardens are coming alive with bees, flies, butterflies, dragonflies, praying mantises, beetles, millipedes, centipedes, and spiders.
For some of us it is exciting to see these strange and wonderful creatures return. For others, it’s a sign to contact the local pest control company or go to the supermarket to stock up on sprays.
But while some bugs do us very few favours – like <a href="https://theconversation.com/the-worst-year-for-mosquitoes-ever-heres-how-we-find-out-68433" target="_blank">mozzies</a>, snails and cockroaches – killing all insects and bugs isn’t always necessary or effective. It can also damage ecosystems and our own health.
There are times when insecticides are needed (especially when pest populations are surging or the <a href="https://theconversation.com/how-we-kept-disease-spreading-asian-tiger-mozzies-away-from-the-australian-mainland-72873" target="_blank">risk of disease is high</a>) but you don’t have to reach for the spray every time. Here are five good reasons to avoid pesticides wherever possible, and live and let live.
<h2>1. Encourage the bees and butterflies, enjoy more fruits and flowers</h2>
<img src="https://images.theconversation.com/files/191979/original/file-20171026-28083-92nvqq.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="">Hover fly. dakluza/flickr
Flowers and fruits are the focal points of even the smallest gardens, and many of our favourites rely on visits from insect pollinators. We all know about the benefits of European honey bees (Apis mellifera), but how about our “home grown” pollinators – our <a href="http://www.aussiebee.com.au/beesinyourarea" target="_blank">native bees</a>, hover flies, beetles, moths and butterflies. <a href="https://australianmuseum.net.au/pollination" target="_blank">All these species contribute to the pollination</a> of our native plants and fruits and veggies.
You can encourage these helpful pollinators by growing plants that flower at different times of the year (especially natives) and looking into sugar-water feeders or <a href="https://www.growveg.com.au/guides/insect-hotels-encourage-beneficial-insects-into-your-garden/" target="_blank">insect hotels</a>.
<h2>2. Delight your decomposers, they’re like mini bulldozers</h2>
<img src="https://images.theconversation.com/files/191978/original/file-20171026-28071-1310clk.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=237&amp;fit=clip" alt="">Slaters improve your soil quality. Alan Kwok
To break down leaf litter and other organic waste you need decomposers. Worms, beetles and slaters will munch through decaying vegetation, releasing nutrients into the soil that can be used by plants.
The problem is that urban soils are frequently disturbed and can contain high levels of heavy metals that <a href="http://www.sciencedirect.com/science/article/pii/S0269749111005719" target="_blank">affects decomposer communities</a>. If there are fewer “bugs” in the soil, decomposition is slower – so we need to conserve our underground allies.
You can help them out with compost heaps and worm farms that can be dug into the ground. It’s also good to keep some areas of your lawn un-mowed, and to create areas of leaf litter. Keeping your garden well-watered will also help your underground ecosystems, but be mindful of water restrictions and encouraging mosquitoes.
<h2>3. An army of beneficial bugs can eat your pests</h2>
Mantises and dragonflies are just some of the hundreds of fascinating and beautiful bugs we are lucky to see around our homes. Many of these wonderful creatures are predators of mozzies, house flies and cockroaches, yet people are using broad-spectrum insecticides which kill these beneficial bugs alongside the pests.
It may sound counterproductive to stop using pesticides in order to control pests around the home, but that’s <a href="https://www.nature.com/nature/journal/v466/n7302/abs/nature09183" target="_blank">exactly what organic farmers do</a>. By reducing pesticides you allow populations of natural enemies to thrive.
Many farmers <a href="http://www.annualreviews.org/doi/abs/10.1146/annurev.ento.45.1.175" target="_blank">grow specific plants to encourage beneficial insects</a>, which has been shown to reduce the damage to their crops.
This form of pest control in growing in popularity because spraying can result in insecticide resistance. Fortunately, it’s easy to encourage these bugs: they go where their prey is. If you have a good range of insects in your yard, these helpful predators are probably also present.
<img src="https://images.theconversation.com/files/193118/original/file-20171102-26426-1kkfe0j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="">Jumping spiders are great at eating flies and other pests. Craig Franke
<h2>4. Your garden will support more wildlife, both big and small</h2>
Spraying with broad-spectrum pesticides will kill off more than just insects and spiders – you’re also going after the animals that eat them. The more insects are around, the more birds, <a href="https://theconversation.com/do-bats-eat-mozzies-or-moths-the-clue-is-in-the-poo-19400" target="_blank">mammals</a>, reptiles and frogs will thrive in your backyard.
Baiting for snails, for example, will deter the blue-tongue lizards that eat them, so cage your vegetables to protect them instead. Keeping your garden well-watered, and including waterbaths, will also encourage a balanced ecosystem (but change the waterbaths regularly).
<h2>5. You and your family be happier and healthier</h2>
Engaging with nature <a href="https://theconversation.com/green-for-wellbeing-science-tells-us-how-to-design-urban-spaces-that-heal-us-82437" target="_blank">increases well-being</a> and <a href="https://www.propertyobserver.com.au/http://www.pnas.org/content/112/26/7937" target="_blank">stimulates learning in children</a>. Insects are a fantastic way to engage with nature, and where better to do this than in your own back yard! Observing and experimenting on insects is a wonderful <a href="http://www.annualreviews.org/doi/abs/10.1146/annurev.ento.42.1.269" target="_blank">teaching tool</a> for everything from life cycles to the scientific method. It will also teach your kids to value nature and live sustainably.
It’s also a hard truth that <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1519137/?page=1" target="_blank">domestic pesticides present a significant risk of poisoning</a>, especially for small children.
In reality, the risk of exposing your children to the pesticides far outweighs the nuisance of having a few bugs around. Instead, integrated pest management, which combines non-chemical techniques like <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1241688/" target="_blank">cleaning of food residues, removal of potential nutrients, and sealing cracks and crevices</a>, is safer for your family and your garden ecosystems.
<h2>Think globally, act locally</h2>
Your backyard has a surprising impact on the broader health of your neighbourhood, and gardens can make <a href="https://kar.kent.ac.uk/28303/1/Davies_et_al._Biological_Conservation_2009.pdf" target="_blank">significant contributions to local biodiversity</a>. Insects are an important part of ecosystem conservation, and encouraging them will improve the health of your local environment (and probably your health and well-being too).
<img src="https://counter.theconversation.com/content/85673/count.gif?distributor=republish-lightbox-basic" alt="The Conversation" width="1" height="1">In the end, insects and spiders are not out to get you. For the sake of our kids and our environment, you should give them a chance.
<a href="https://theconversation.com/profiles/lizzy-lowe-92423" target="_blank">Lizzy Lowe</a>, Postdoctoral researcher, <a href="http://theconversation.com/institutions/macquarie-university-1174" target="_blank">Macquarie University</a>; <a href="https://theconversation.com/profiles/cameron-webb-6736" target="_blank">Cameron Webb</a>, Clinical Lecturer and Principal Hospital Scientist, <a href="http://theconversation.com/institutions/university-of-sydney-841" target="_blank">University of Sydney</a>, and <a href="https://theconversation.com/profiles/kate-umbers-416078" target="_blank">Kate Umbers</a>, Lecturer in Zoology, <a href="http://theconversation.com/institutions/western-sydney-university-1092" target="_blank">Western Sydney University</a>.
This article was originally published on <a href="http://theconversation.com" target="_blank">The Conversation</a>. Read the <a href="https://theconversation.com/five-reasons-not-to-spray-the-bugs-in-your-garden-this-summer-85673" target="_blank">original article</a>.
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j.ballantyne1990-6AQqhLzZaK

Five reasons not to spray the bugs in your garden this summer

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<img src="https://counter.theconversation.edu.au/content/68499/count.gif?distributor=republish-lightbox-basic" alt="The Conversation" width="1" height="1">
GUEST OBSERVER
In our recent study we found that 40 percent of 203 Sydney homes we sampled contain lead in garden soil above the Australian health guideline of 300 milligrams per kilogram (mg/kg). 
This presents a hazard because soil lead can adhere to or get absorbed into edible plants. An additional pathway of exposure occurs when contaminated soil dust enters homes and is accidentally ingested. Lead is a potent neurotoxin that affects childhood development. 
<h2>Urban agriculture and VegeSafe</h2>
Urban agriculture is becoming more popular across Australia. Almost half (48%) of all households in metropolitan areas are now growing some form of edible produce.
Most lead contamination is a result of the historical use of lead petrol and lead-based paint (now phased out) and previous industrial emissions. Scientists and regulators are well aware of these legacy issues, but the general public remains underinformed about the potential risks. 
To help urban gardeners assess contamination risks associated with their garden soils, we started the community science initiative VegeSafe in 2013. This program offers free soil metal screening to participants.
Each participant receives a formal report on their soil metal results and advice about what to do next if soils contain elevated concentrations of metals. We have provided 5,500 free soil metal tests to over 1,300 homes and community gardens (Australia-wide), the largest program and study of its kind in Australia. 
<h2>What did we find?</h2>
As well as the 40% of Sydney gardens containing soil above the 300 mg/kg Australian health guideline, approximately one in seven homes had soils lead levels greater than 1,000 mg/kg. Soil metal concentrations were typically greatest around drip lines. 
Soil lead concentrations were greatest in the City of Sydney and former local government areas of Leichhardt Municipal Council and Marrickville Council, which had mean soil lead concentrations of 883 mg/kg, 960 mg/kg and 689 mg/kg, respectively. 
<a href="https://www.propertyobserver.com.au/images/2017/01/17/image-20161122-14964-1w7krx6.jpg" target="_blank">Click to enlarge</a>
<img src="https://res.cloudinary.com/dz9xllyip/image/fetch/c_scale,w_580,q_auto:good/https://s3-ap-southeast-2.amazonaws.com/po.images/2017/01/17/image-20161122-14964-1w7krx6.jpg" alt="">
Soil lead concentrations of vegetable garden soils from 141 Sydney homes. Map represents one of four areas around homes (front yard, drip line, back yard and vegetable garden) in this study. Source: Rouillon et al. 2016
Homes with painted exteriors built before 1970 were more likely to have soils contaminated with lead. The highest levels are at homes 80 years or older. This is likely to have been caused by lead-rich paint, which contained up to 50% lead prior to 1970. Lead in paint was reduced to less than 1,000 mg/kg (0.1%) by 1997. 
We observed the environmental benefit of the withdrawal of lead from paints and leaded petrol (removed in 2002) in our study. Garden soils at newer homes contain the least lead. Soil lead concentrations decrease with distance from Sydney’s city centre, where there are more old homes and greater density of traffic and industry. 
<a href="https://www.propertyobserver.com.au/images/2017/01/17/image-20161122-10973-1aft5jx.png" target="_blank">Click to enlarge</a>
<img src="https://www.urban.com.au/images/2017/01/17/image-20161122-10973-1aft5jx.png" alt="">
Cross-section schematic of a typical inner-Sydney residential home with median soil Pb (lead) concentrations for painted pre-1970 homes, non-painted pre-1970 homes, post-1970 homes and reference homes. The vegetable garden is displayed at the rear of the back yard, as this was the case for the majority of homes. Source: Rouillon et al. 2016
<h2>Public health</h2>
Lead exposure is especially detrimental for children because their neurological and skeletal systems are developing. Adults are also adversely affected, with studies showing increased blood pressure and hypertension associated with sub-clinical exposures.
Toxicological evidence also shows that exposure reduces semen quality and extends the time to pregnancy. In short, lead is detrimental to all human systems and exposures should be avoided or minimised at all times.
Our study demonstrates lead contamination in garden soils is greater at painted homes than non-painted homes. Many pre-1970 Australian homes still contain paint with up to 50% lead on exterior walls, fences, eves, doors and window frames. 
The main risk of exposure arises when lead-based paint deteriorates or is removed improperly. Indeed, many home renovators unwittingly expose themselves and others due to a lack of knowledge of lead hazards.
Paints containing lead are no longer used in Australia, but remain on countless homes.
<h2>Reducing exposure</h2>
The United States Environmental Protection Agency introduced legislation specifically targeting houses with lead paint to prevent contamination and to minimise avoidable lead exposures. 
Unfortunately this regulatory gap has not been filled in Australia. Despite the widespread historic use of lead-based paints and the high proportion of exposure related to it, our data reveals a concerning legacy of soil lead contamination in older suburbs. 
We recommend that people residing at or planning to purchase or renovate homes built before 1970 should get their soils and paint tested for lead. Using a qualified lead-abatement decorator in older homes would also help prevent exposure. Where parents and homeowners think they may have caused exposure, their GPs can provide a blood lead test. 
Reducing even low-level exposures is critical, as demonstrated by Bruce Lanphear’s “prevention paradox” (see the image below). The graphic illustrates that the most IQ points across a population are lost from low-level lead exposures. 
<a href="https://www.propertyobserver.com.au/images/2017/01/17/image-20161122-14944-ruxd0e.jpg" target="_blank">Click to enlarge</a>
<img src="https://res.cloudinary.com/dz9xllyip/image/fetch/c_scale,w_580,q_auto:good/https://s3-ap-southeast-2.amazonaws.com/po.images/2017/01/17/image-20161122-14944-ruxd0e.jpg" alt="">
<div class="enlarge_hint"> </div>
Bruce Lanphear’s prevention paradox. The majority of IQ points lost to lead exposure occurs in children who have low-to-moderate exposure to lead. Adapted from Reference (Lanphear 2015)
<h2>What can gardeners do?</h2>
Where non-food-growing soils exceed the Australian soil metal guidelines, we recommend maintaining year-round cover of lawn or mulch to minimise dust generation. 
Where metal guidelines are exceeded in food-growing soils, we recommend either replacing existing soil with new, uncontaminated soil, or relocating the food garden to an above-ground vegetable plot (again with new soil). 
In this way, gardeners can exercise our motto, which is to carry on gardening knowing their soils are clean.
<a href="https://theconversation.com/profiles/marek-rouillon-139693" target="_blank">Marek Rouillon</a> is PhD Candidate, Macquarie University.
<a href="https://theconversation.com/profiles/louise-kristensen-124418" target="_blank">Louise Kristensen</a> is postdoctoral research fellow, Macquarie University.
<a href="https://theconversation.com/profiles/mark-patrick-taylor-11394" rel="author">Mark Patrick Taylor</a> is professor of Environmental Science, Macquarie University.
<a href="https://theconversation.com/profiles/paul-harvey-106637" target="_blank">Paul Harvey</a> is researcher of Environmental Science, Macquarie University.
<a href="https://theconversation.com/profiles/steven-g-george-317844" target="_blank">Steven G George</a> is researcher of Environmental Science, Macquarie University.
All are authors for The Conversation.
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jchancellor-FAypfDUnLy

Elevated lead levels in Sydney backyards: here’s what you can do

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<img src="https://counter.theconversation.edu.au/content/66137/count.gif" alt="The Conversation" width="1" height="1">
GUEST OBSERVER
It is with great sadness that I acknowledge the passing of Bill Mollison on Saturday, September 24 (1928-2016). He was one of the true pioneers of the modern environmental movement, not just in Australia but globally. 
Best known as co-originator of the “permaculture” concept with David Holmgren, and recipient of the Right Livelihood Award in 1981, Mollison helped develop a holistic body of environmental theory and practice which is widely recognised as one of Australia’s finest and most original contributions to the global sustainability challenge.
<h2>A brief history of permaculture</h2>
Mollison grew up in Stanley, Tasmania. After leaving school at 15 he moved through a range of occupations before joining the CSIRO in the Wildlife Survey Section in 1954, where he developed his research experience and understanding of ecological systems. 
He was later appointed to the University of Tasmania, which is where, in 1974, he met the brilliant and radical young research student, David Holmgren
The collaboration between Mollison and Holmgren resulted in the permaculture concept, culminating in the publication of their seminal work, Permaculture One in 1978, which sparked the global movement.
<h2>What is permaculture?</h2>
Permaculture defies simple definition and understanding. The term began as a fusion of “permanent” and “agriculture”. Even back in the 1970s, Mollison and Holmgren could see how destructive industrial agriculture was to natural habitats and topsoils, and how dependent it was on finite fossil fuels. 
It was clear that these systems were unsustainable, a position ratified by scientific reports today which expose the alarming effects industrial agriculture has on biodiversity and climate stability. The two pioneering ecologists began to wonder what a “permanent agriculture” would look like. Thus permaculture was born.
In the broadest terms, permaculture is a design system that seeks to work with the laws of nature rather than against them. It aims to efficiently meet human needs without degrading the ecosystems we all rely on to flourish. 
Put otherwise, permaculture is an attempt to design human systems and practices in ways that mimic the cycles of nature to eliminate waste, increase resilience and allow for the just and harmonious co-existence of human beings with other species.
A wide range of design principles were developed to help put these broad ideas and values into practice. This practical application and experimentation is what really defines permaculture. Before all else, participants in the movement get their hands in the soil and seek to walk the talk. 
There is now a vast array of excellent books detailing the practice of permaculture, as well as outstanding websites such as the Permaculture Research Institute for those wanting to learn, share, explore and connect.
Although permaculture was initially focused on sustainable methods of organic food production, the concept soon evolved to embrace the broader design challenges of sustainable living – not just “permanent agriculture”, but “permanent culture”.
Today we face profound environmental and social challenges: ecological overshoot, climate instability, looming resource scarcity, and inequitable concentrations of wealth. In such a world the permaculture ethics of “care of people, care of planet, and fair share” imply radical changes to the way we live with each other and on the planet. 
As well as transitioning away from fossil-fuel-dependent agriculture toward local organic production, permaculture implies the embrace of renewable energy systems, “simple living” lifestyles of modest consumption, as well as retrofitting the suburbs for sustainability and energy efficiency.
From a grassroots or community perspective, the transition towns and ecovillage movements acknowledge their profound debts to permaculture. 
From a macroeconomic perspective, permaculture implies a degrowthtransition to a steady-state economy that operates within the sustainable limits of the planet. Permaculture even has implications for what alternative forms of global development might look like.
So, in answer to the complex question “what is permaculture?”, perhaps the most concise response is to say with others that “permaculture is a revolution disguised as organic gardening”.
<h2>Bill Mollison’s legacy: a challenge to us all</h2>
Despite developing into a thriving global movement, permaculture still has not received the full attention it deserves. As the world continues to degrade ecosystems through the poor design of social and economic systems, it has never been clearer that permaculture is a way of life whose time has come.
Nevertheless, permaculture is not a panacea that can answer all challenges. Permaculture is not without its critics (see, for example, here and here). But I would argue that the lens of permaculture can certainly illuminate the path to a more sustainable and flourishing way of life, such that we ignore its insights at our own peril.
Thank you, Bill Mollison, for the inspiration and insight – and the challenge you have left us with to design a civilisation that regenerates rather than degrades our one and only planet. May humanity learn the lessons of permaculture sooner rather than later.
Only then, I suspect, will “Uncle Bill” rest in peace.
Samuel Alexander is research fellow, Melbourne Sustainable Society Institute, University of Melbourne and author for The Conversation. He can be contacted <a href="https://theconversation.com/profiles/samuel-alexander-102353" target="_blank">here</a>.
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A revolution disguised as organic gardening: in memory of Bill Mollison

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<img src="https://counter.theconversation.edu.au/content/65643/count.gif" alt="The Conversation" width="1" height="1">
GUEST OBSERVER
Gardening is good for your health, but it can pose some risks if you’re not careful. For example, you should use sensible protection against the sun to prevent cancer, a significant cause of death in Australia.
Gardening in Australia also requires, to varying degrees depending where in the country you are, pesticides, herbicides and fertilisers. There is an enormous number of agents with multiple formulations, depending on what you are doing, what plants you are tending, the size of your garden and the kind of soil. 
These garden treatments are designed to be specific and potent, so they can be applied less often and work (mostly) only on the things you want them to work on. All of them – even the “natural” ones such as sulfur dusts to control caterpillars and mildew – are chemicals, which means they have health risks. 
<h2>Regulation of chemicals</h2>
While not perfect, gardening product safety is regulated in Australia. Let me introduce you to the Australian Veterinary Medicines and Pesticides Authority. This body regulates pesticide (a substance that kills pests such as insects and weeds) and herbicide (a substance that kills only weeds) products sold in Australia. 
The AVPMA regularly reviews products for safety concerns, though the reviews may be decades apart. It co-ordinates with World Health Organisation bodies and its counterparts in Europe, Canada and the United States. 
Given the sheer number of compounds and formulations available, I can’t possibly cover the safety of all chemicals, or even all groups of chemicals. If you are concerned about a particular product, you can search the AVPMA site for the ingredients in a given pesticide, herbicide or fertiliser. 
This may be tricky, as some will not necessarily have a chemical name on them, just the trade name. However, most pesticides and herbicides from reputable companies should have a material safety data sheet (MSDS) with them. This should give you the details you need to check through the AVPMA site.
<h2>Pesticides</h2>
There are three ways to deal with pests (well, four if you count laboriously picking them off your plants): repel, smother or poison them. All these can harm people if they are exposed to significant quantities. But in an urban garden, exposure to pesticides is typically small and of limited duration.
Common smothering pesticides are oils such as petroleum oils used to control, say, leaf pests on citrus, or pests in a variety of other circumstances. If you apply these often, without gloves, you might get skin irritation; or lung irritation if you breath the spray in. So always follow the directions, which include wearing gloves and spraying so the wind doesn’t blow the spray back into your face.
Modern poisoning insecticides include the pyrethrums which are found naturally in some chrysanthemum flowers. Both the natural pyrethrum and synthetic pyrethroids have low toxicity to humans – particularly at the doses found in garden products. Continuous use of pyrethroid insecticides has no health implications for humans if instructions are followed.
Neonicotinoids are synthetic insecticides that mimic nicotine, which is toxic to insects. These have a place in pest control if used thoughtfully and sparingly. Unlike pyrethroids, these insecticides target a pathway in the insect nervous system shared with humans, so could potentially harm us.
When used as directed, poisoning should not occur and animal studies suggest human exposure should not lead to significant health effects. Neonicotinoids are toxic to bees, although Australia has not had the big bee crash seen in the US and parts of Europe.
Chronic use of neonicotinoids in a human gardening population has not been assessed for long-term health effects, but a small study of agricultural workers has shown no effect of chronic exposure. Another small study, however, suggests some association with memory loss. 
<h2>Herbicides</h2>
Again, there is a bewildering variety of herbicides, depending on what weedy species is being targeted and how the weed is being killed. 
Right out of the gate is glyphosate, used for broadleaf weeds. This chemical, commonly sold as Roundup, caused some controversy after the International Agency for Research on Cancer (IARC) concluded it was a probable human carcinogen. 
However, the IARC’s determination was based on only a small number of animal studies and didn’t include a number of animal studies where glyphosate did not cause cancer. It also said nothing about risk; that is, what is the likelihood glyphosate would cause cancer at the concentrations humans are usually exposed to? 
The European Food Safety Authority and the AVPMA have evaluated the evidence and determined that under appropriate handling conditionsapplicable to general backyard gardeners, there is no risk to humans.
As a comparison, a homemade herbicide of salt, vinegar and soap that is claimed as a replacement for glyphosate is more toxic than glyphosate.
Another herbicide for woody weeds, like blackberry, is Triclopyr. This can cause eye and skin irritation, but has no serious long-term health impacts if proper safety procedures are followed.
<h2>Fertilisers</h2>
There are many formulations and varieties of fertilisers depending on soil type and location (where I live is basically sand). Health risks are basically related to long-term inhalation of fine particles, which could cause breathing difficulties. Once again follow the safety instruction.
<h2>Caveat</h2>
Just because a given product is not, or minimally, toxic to humans, that does not mean you should apply it to your garden by the bucket load. Always apply any garden chemical with care and thought, using the right amount at the right time for the right purpose.
Any agent you apply or spray can cause adverse reactions if you don’t use it as directed. Getting “organic” garlic and soap insecticide spray in your eyes will hurt like billy-o, just like the latest you-beaut synthetic pyrethrum spray, even though both are pretty much non-toxic to humans. 
Inhaling dusts can irritate your lungs. Always make sure you are wearing gloves, apply sprays and dusts downwind and wear goggles if necessary. Always follow the directions.
Ian Musgrave is senior lecturer in Pharmacology, University of Adelaide and author for The Conversation. He can be contacted <a href="https://theconversation.com/profiles/ian-musgrave-1808" target="_blank">here</a>.
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Are common garden chemicals a health risk?

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<img src="https://counter.theconversation.edu.au/content/65332/count.gif" alt="The Conversation" width="1" height="1">
GUEST OBSERVER
Most people think of soil only in terms of the dirt that sticks stubbornly to their hands and shoes. But soil is much more than that.
A handful of soil is a small and very complex ecosystem which includes soil particles, pores, aggregates, organic matter and a staggering number of microorganisms, all of which interact to keep the soil healthy and productive.
Each soil is different. The primary factor determining the physical properties of a soil is particle size. Sandy soils have a coarse structure, large pores and little ability to hold on to water and nutrients, which makes them prone to leaching.
Clayey soils hold nutrients and water, but because the pores are small they are prone to waterlogging.
The pores between soil particles are important for water flow but also for the movement of gases. Particularly important is the exchange of oxygen with the atmosphere, because plant roots and most soil organisms need oxygen to breathe.
Sand, silt and clay particles are bound together to form aggregates. These aggregates form the skeleton, or matrix, for chemical and biological processes which are critical for soil functions.
<h2>Nitty-gritty</h2>
Organic matter and soil microorganisms play key roles in the formation and stability of aggregates.
Think of organic matter as being the glue or mortar between soil particles. But the organic matter needs be decomposed to be most effective. And this is where soil microorganisms come in.
Each gram of soil contains a billion bacteria, which is almost as much as the human population of China or India, and about 50 times the number of people in Australia.
And this number does not even include soil fungi. All these bacteria and fungi can coexist because they have different needs or don’t interact.
For example, a bacterium on one side of the aggregate is quite isolated from a bacterium on the other side of the same aggregate. So even if these two bacteria have similar needs, they don’t compete.
They may also not compete because they are not active at the same time. In a given soil condition, only a small proportion of the bacterial population is active. The majority are inactive (dormant) and come to life only when conditions are optimal for them.
Another reason for the staggering number of microbes in a gram of soil is the huge diversity. A gram of soil contains around a million different species. Among them are generalists but there are also specialists, such as those capable of fixing nitrogen from the atmosphere or degrading wood.
The food of the vast majority of soil microbes is organic matter, which is mainly plant matter. When plant matter gets into the soil, it is attacked by soil microbes for energy and nutrients.
This attack is aided by soil animals such as earthworms or mites. They mix the plant matter in the soil and its microbes, fragmenting it and thereby improving contact between plant matter and soil organisms.
During decomposition of plant matter, microbes multiply and produce carbon dioxide and nutrients for plant uptake. The dead microbes and the components of the plant matter that are very difficult to decompose help to bind the soil particles together.
This binding is also aided by slimes produced by microbes and the long filaments of <a href="https://website.nbm-mnb.ca/mycologywebpages/NaturalHistoryOfFungi/Thallus">fungal hyphae</a>. The aggregates formed in this way are stable, which is important for adequate water and air supply for plant roots and soil organisms.
If aggregates are not stable, such as in sodic soils, water and air supply are restricted and plants and soil organisms will suffer.
<h2>Feeding your soil</h2>
Maintaining a certain level of organic matter in soil is critical for sustained soil health and function. Organic matter not only ensures that aggregates are stable, but also acts like a sponge, holding water, which is particularly important in sandy soils.
Another important function of organic matter is supply of nutrients required by plants. As mentioned above, decomposition of plant matter releases nutrients and it also can bind nutrients which can become available later.
But organic matter also decomposes, so needs to be replaced regularly. You can do this by adding plant matter growing in your garden or from outside to the soil, either directly or after composting.
Compost is more stable in soil than litter or straw because it is already decomposed during the composting process. It is a good glue for soil particles and binds nutrients, but it will not supply much nutrients for plants.
Fresh young plant matter is a good source of nutrients, but also decomposes very quickly and may initially release more nutrients than the plants can take up.
Mature cereal straw is nutrient-poor and decomposes slowly. So for good nutrient supply and long-term soil productivity, you may have to supply a mix of different types of organic amendments.
Of course, you can bypass this organic loop by adding inorganic fertilisers. Plants will grow well, but you have to match supply and plant demand carefully, because most fertilisers are dissolved quickly.
In your garden, you may get the best results by combining organic and inorganic fertilisation: various organic amendments for long-term soil health and stability, and inorganic fertiliser to overcome short-term nutrient deficiencies.
Petra Marschner is professor of Agriculture, University of Adelaide and author for The Conversation. She can be contacted <a href="https://theconversation.com/profiles/petra-marschner-299098" target="_blank">here</a>.
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Fertile ground: what you need to know about soil to keep your garden healthy

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<img src="https://counter.theconversation.edu.au/content/65251/count.gif" alt="The Conversation" width="1" height="1">GUEST OBSERVER
“That’s all very well put,” says Candide, in the final line of Voltaire’s novel of the same name, “but we must go and work our garden.”
I studied this text at high school before I became a gardener and professional horticulturist. We were taught that Candide’s gardening imperative was metaphorical not literal; a command for finding an authentic vocation, not a call to take up trowels and secateurs.
In fact, Voltaire himself really believed that active gardening was a great way to stay sane, healthy and free from stress. That was 300 years ago.
As it turns out, the science suggests he was right.
The science of therapeutic horticulture
Gardens and landscapes have long been designed as sanctuaries and retreats from the stresses of life – from great urban green spaces such as Central Park in New York to the humblest suburban backyard. But beyond the passive enjoyment of a garden or of being in nature more generally, researchers have also studied the role of actively caring for plants as a therapeutic and educational tool.
“Therapeutic horticulture” and “horticultural therapy” have become recognised treatments for stress and depression, which have served as a healing aid in settings ranging from prisons and mental health treatment facilities to schools and hospitals.
Gardening and school
Studies of school gardening programs – which usually centre on growing food – show that students who have worked on designing, creating and maintaining gardens develop more positive attitudes about health, nutrition and the consumption of vegetables.
They also score better on science achievement, have better attitudes about school, and improve their interpersonal skills and classroom behaviour.
Research on students confirms that gardening leads to higher levels of self-esteem and responsibility. Research suggests that incorporating gardening into a school setting can boost group cohesiveness.
Gardening and mental health
Tailored gardening programs have been shown to increase quality of life for people with chronic mental illnesses, including anxiety and depression.
Another study on the use of therapeutic horticulture for patients with clinical depression sought to understand why gardening programs were effective in lessening patient experience of depression. They found that structured gardening activities gave patients existential purpose. Put simply, it gave their lives meaning.
In jails and corrective programs, horticultural therapy programs have been used to give inmates positive, purposeful activities that lessen aggression and hostility during and after incarceration.
In one detailed study from a San Francisco program, involvement in therapeutic horticulture was particularly effective in improving psychosocial functioning across prison populations (although the benefits were not necessarily sustained after release.)
Gardening has been shown to help improve the lives of military veteransand homeless people. Various therapeutic horticulture programs have been used to help people with learning difficulties, asylum seekers, refugees and victims of torture.
Gardening and older people
As populations in the West age, hands-on gardening programs have been used for older people in nursing homes and related facilities.
A systematic review of 22 studies of gardening programs for older adults found that gardening was a powerful health-promoting activity across diverse populations.
One study sought to understand if patients recovering from heart attack might benefit from a horticultural therapy program. It concluded:
[Our] findings indicate that horticultural therapy improves mood state, suggesting that it may be a useful tool in reducing stress. Therefore, to the extent that stress contributes to coronary heart disease, these findings support the role of horticultural therapy as an effective component of cardiac rehabilitation.
While the literature on the positive effects of gardening, reflecting both qualitative and quantitative studies, is large, most of these studies are from overseas.
Investment in horticultural therapy programs in Australia is piecemeal. That said, there are some standout success stories such as the Stephanie Alexander Kitchen Garden Foundation and the work of nurse Steven Wells at the Royal Talbot Rehabilitation Centre and beyond.
Finally, without professionally trained horticulturists none of these programs – in Australia or internationally – can take place.
Chris Williams is lecturer in urban horticulture, University of Melbourne and author for The Conversation. He can be contacted <a href="https://theconversation.com/profiles/chris-williams-300083" target="_blank">here</a>.
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