Compost is made by combining organic waste than provides nitrogen and/or carbon. The advice to make compost from waste that is green (provides nitrogen) and brown (provides carbon) is a bit confusing when manure contains a lot of nitrogen, but most of it is brown. When suitable dampened materials are combined in a heap that has contact with the soil, heat is generated and millions of aerobic bacteria get to work transforming the fuel into a compost-making factory.
Manure from animals that eat grass (lots of nitrogen)
Chicken manure (lots of nitrogen)
Weeds without seed heads (nitrogen and carbon)
Lawn cuttings that have wilted (nitrogen and carbon)
Green prunings – shredded (nitrogen and carbon)
Raw vegetables and fruit – chopped for fast break down (nitrogen and carbon)
Uncooked kitchen waste – including tea bags and coffee grounds (nitrogen and carbon)
Old plants – chopped for fast break down (nitrogen and carbon)
Bedding straw for animals that eat grass or seeds (lots of nitrogen and carbon)
Straw and hay (lots of carbon)
Cardboard boxes and egg cartons – shredded (carbon)
Undyed wool, feathers and hair (nitrogen and carbon)
In Small Amounts
Newspaper and waste paper – separate sheets crumpled or roughly shredded (carbon)
Woody prunings – shredded (carbon)
Wood shavings – (very slow to break down and tie up a lot of nitrogen)
Seaweed – well-washed (helps factory work faster)
Herbs – comfrey, yarrow and chamomile (help factory work faster)
Egg shells – crumbled (keep compost smelling sweet and earthy)
Do Not Add
Plastic or foil containers, wrapping or disposable nappies
Fruit or vegetables that have been attacked by fruit fly or codling moth (larvae can pupate in factory)
Plants with diseases
Cat, dog or human faeces* (these can spread diseases through compost)
Rats or mice* (can spread diseases through compost)
Grey water (upsets pH balance and slows process)
Soil – makes compost heavy and harder to turn (amount clinging to weed roots is sufficient)
Earthworms – the initial heat will kill them. Earthworms know when to move into a compost factory.
Synthetic fertilisers (delays process and deters earthworms)
If you only have small quantities of organic waste to recycle, a worm farm would be a better solution. See Compost Worm Farm.
For information on how compost makes garden soil healthy, see Compost. ** Cat and dog faeces, and vermin, can be composted anaerobically in a small pit or container, but this compost should not be added to garden beds.
Composting recycles organic waste into a product that makes garden soil healthy. Mature compost is a dark brown, sweet-smelling material that can be added to topsoil.
There are two ways to make compost – aerobic, which requires aeration during the process, and anaerobic, which is a slow, rather smelly process. Mature aerobic compost can be produced in about 6–8 weeks in most areas of Australia.
How does compost make garden soil healthy?
Compost keeps soil more moisture-retentive, yet better-drained.
Compost provides food for earthworms that increase the depth of fertile topsoil by leaving digested food along their deep tunnels.
Compost provides food and a home for the many helpful bacteria and fungi that help protect soil from soil-borne diseases.
Well made compost has a pH of 6.5 – where all plant nutrients are fully available, and the perfect pH for the majority of plants.
Compost buffers plant roots from an unsuitable pH in surrounding soil.
It also insulates plant roots from temperature extremes so that soil stays cooler in summer and warmer in winter.
Compost contains all the minerals that plants, animals and humans need for good health, most of the soil’s nitrogen, plus lots of humus that forms the most stable part of recycled organic waste.
Humus and the minerals that plants need both carry a weak electrical charge. The electric charge holds the plant food minerals close to plant roots and prevents them from washing away in heavy rain.
Humus is able to control the release of trace elements needed in tiny amounts, and block absorption of poisonous metals in soil so that they do not end up in our food.
Humus stores carbon in soil for very long periods of time.
Humus, in compost, provides a habitat for a soil community of billions of beneficial bacteria and fungi that perform important functions.
Some bacteria species in humus make a ‘glue’ that is able to hold soil particles in a way that improves the flow of water and air through soil. This improves the structure of soil so that plant roots grow more easily. Strong roots help plants to resist the effects of drought and storms.
Mycorrhiza fungi in humus stick like hairs to the roots of plants, helping them absorb water and nutrients in exchange for sugars produced by plants during photosynthesis. Some 95% of perennial plants rely on mycorrhiza for healthy growth.
For organic gardeners who don’t have enough recyclable waste for a productive compost heap, a compost worm farm is the answer.
Compost worms are different from earthworms that tunnel through soil and move into compost heaps after organic matter has been partly processed by microorganisms. Consequently, the term ‘compost worms’ can be confusing to new gardeners. Worm farm (compost) worms require a moister and cooler environment than earthworms (10–30° C.), and feed on a wide range of organic matter, including vegetable and fruit waste (except for citrus and onions), wet paper and cardboard, grass clippings, aged cow and horse manure, soft weeds and hair. Chopping waste into small pieces provides a larger surface area for worms to feed on and speeds up production. The digested waste (worm castings) are a clay-like humus that contains all the nutrients and trace elements that plants need for good health in a form that plant roots can absorb immediately.
Worm castings are Nature’s slow-release, complete organic fertiliser. The more varied the worms’ diet, the better the fertiliser. Simply rake the worm castings into the topsoil on garden beds. As they do not smell, they are the perfect fertiliser for both indoor and outdoor pot plants. They are also a great addition to seedling mixes and, when diluted to very weak black tea strength, the liquid that drains from the worm farm is a fertiliser that gets seedlings off to a flying start.
Worm farming has become a very popular method of recycling and various commercial worm farms are available to suit different situations. Most children find worm farms fascinating and enjoy looking after them.
Commercial worm farms come with complete instructions, a starter colony of worms and edible bedding for the worms. Small commercial farms with several tiers are easily moved into a shed or garage in areas where frosts occur. Or, in frost-free areas, if you can find an old hip bath or large sink, you can make your own worm farm as we have here. Worm farming
Containers with a drainage hole prevent moisture build up in the base of the farm and a waterproof cover excludes light and rain. (Avoid using old carpet or underlay as a cover as these are impregnated with pesticides.)
Add a little water to the farm when necessary to keep the food and bedding damp.
A light dusting of dolomite every few weeks will keep the worm farm smelling sweet and the pH close to perfect.
HARVESTING WORM CASTINGS Worms in farms with stacked trays will move up into the next highest layer when all the food in their tray has been eaten, and it is time to collect the worm castings.
Uncover the worm farm and leave the surface exposed for 15-20 minutes. The worms will move down through the castings away from the light. The castings will contain worm eggs. These are easily recognised as you can see in the photo. They are about the size of the head of a match, or a little bit smaller. Worms don’t lay their eggs in groups like some insects do. They lay them one at a time through the worm castings, but usually close to where they can find food when they hatch. Use a scoop to collect a layer of castings from the top of the farm. A scoop can be made from a 2 litre juice bottle with a handle. Spread the castings onto an old tray by lightly brushing the castings with gloved hands. Check for worm eggs and any small worms that might still be in the castings and put them safely back into the farm. Cover them with a layer of food.
Then tip the collected worm castings into a bucket and collect another scoop full of castings until you have enough to put into your garden bed, or to make ‘worm tea’.
It is wise to test the pH of compost (including homemade compost) before adding it to your topsoil because the pH of topsoil determines which nutrients are available to plants. Well-made aerobic compost has a pH of around 6.0 to 6.5. Unfortunately, I didn’t follow my own advice recently when, temporarily short of homemade compost, we purchased from our local Bunnings store some bags of Richgro ‘All Purpose Organic Compost’ registered as an allowed input by BFA.
I noticed that the transplanted seedlings where I had applied the compost were not making any growth although the rest of the vege patch was doing well. And, in the area where I had mixed extra compost through each planting hole, the seedlings had turned yellow – a clear sign that the soil pH was too high for the plants to absorb phosphorus for root growth, or iron. Iron (along with nitrogen and magnesium) is essential for chlorophyll (green colouring) formation in leaves that allows plants to produce carbohydrates for growth. Iron deficiency (iron chlorosis) starts in the tips of plants and the leaves of the whole plant turn yellow between the veins or, in extreme cases, white. In contrast, nitrogen chlorosis starts in the older leaves because, when nitrogen is in short supply, plants transfer the available nitrogen to the growing tips, and magnesium deficiency starts in the margins of older leaves.
I tested the topsoil of the affected areas and, finding it above 7.5, I then tested the Richgro compost and the reading was between 8.0 and 8.5. As the pH scale is expressed as negative logarithms, a reading of 8.0 means that the soil is ten times more alkaline than a neutral reading of 7.0. This week I received a question from a blog reader who is having difficulty reducing his soil pH. He had also used the same brand of compost, bought from Bunnings in WA.
Richgro’s response that their “internal records” of the batches in question show a pH of 7.1 and 7.2 and that the test kit I used “do not work well with high organic fraction soils or composts” blah, blah, is not consistent with the physical symptoms of the seedlings. I suspect the problem may have been caused by the type of timber used to produce biochar added to the product. Wood ash contains a very reactive form of calcium and, as the ‘Gardening with Biochar’website states, “Raising soil pH is biochar’s most important contribution to influencing soil quality“.
* I must add that Bunnings were quite happy to accept return of the unopened bags of compost after I explained the problem.
To test pH
Add equal quantities of topsoil from the bed you are preparing and the compost you intend to use to a clean bucket. Mix thoroughly, then mix again. Test a sample of the mixture according to the instructions on your soil test kit. Ideally, for healthy growth of most plants, the pH reading should be between 6 and 7.2.
If soil pH is higher than this, please see:‘Changing soil pH’
Also see: ‘What’s soil pH?’
A reader has found that the soil around his fruit trees has become quite hard and has asked should he dig around the trees to loosen the soil.
It is not a good idea to dig around fruit trees as citrus, for example, have very shallow roots. Digging around these and stone fruit trees will damage roots and quite often cause suckers to grow from the root stock. Avocado trees deeply resent any root disturbance.
Hard soil can be a problem in extreme weather conditions, particularly if the soil has not been covered with mulch. If the area is weedy, cut off the weeds at ground level rather than pulling, or digging, them out. Plants obtain most of their energy for growth from light. As you are going to deprive them of light with this method, you can leave the roots to break down and add organic matter to the topsoil.
If grass has covered the area, cut it short and, with a sharp edged spade, cut through the runners 20 cm outside the ‘drip line’ of the tree, which is the area of soil directly below the outside edge of the foliage canopy of the tree – so called because it is where rain drips off the foliage canopy and the feeder roots of trees lie in this area.
Apply a light application of organic complete fertiliser to the soil surface in the drip line area and give the tree a thorough watering, but not close to the trunk. Immediately after watering, cover the soil surface beneath the tree out to the drip line with a 3 cm layer of compost, keeping the compost at least a hands width from the trunk. Compost contains microorganisms (and often earthworms) that will help break down the weed roots and make the soil more friable.
Then cover the compost with a 5 cm layer of organic mulch to keep compost damp and deter weed growth, keeping the mulch well clear of the trunk and extending it to 20 cm beyond the drip line of the tree. Don’t use compost as mulch, as it will dry out and you will lose most of its benefits.
If you tend to accumulate wood ash from log fires over the colder months, you might be tempted to use it instead of lime to raise soil pH, as it contains between 45–50% calcium carbonate. It will certainly do that – but it should only be used on soils with a pH lower than 5.5 because the calcium in wood ash is in a highly soluble form that can change pH very quickly, and it is very easy to over-do the application. Ash from hardwoods contain one third more nutrients than ash from softwoods (e.g. pine).
Apply wood ash only to beds that are not going to be used for a while, using one handful per square metre. Test soil pH after 2 weeks to see if soil is in a more suitable pH range for plant growth. Wood ash should never be used near plants that prefer acid soils.
A safer way to use wood ash is to keep it in a covered container near your compost heap and dust it, instead of garden lime, between layers of other materials that you add to the compost heap. This will help to keep the compost heap sweet-smelling and ensure good microorganism activity. Mature compost holds nutrients in balance and compost containing wood ash can safely be applied to garden beds.
Wood ash can also be dusted over lawns that have become ‘sour’, especially where moss is growing. While the calcium improves the soil pH, the 2–8% potassium (potash) in wood ash will improve the lawn’s tolerance to heat and cold as well as improving disease resistant. However, if applying wood ash to lawns, avoid using seaweed fertiliser for the current season as seaweed also contains a considerable amount of potassium. Too much potassium can cause a magnesium deficiency.
I’ve had several e-mails recently from gardeners who have used purchased soil or organic fertilisers and found that their plants were sickly or not growing because they were growing in soil that is too alkaline.
Soil pH (acidity or alkalinity of soil) is extremely important because determines which nutrients are available to plants. All the major nutrients are only freely available to plants within a narrow soil pH range of 6.5 to 7.5, where essential trace elements are also available, and aluminium is locked out.
See What’s soil pH?
Lime should only be added to soil where testing of soil pH shows a need for it. Mushroom compost and poultry manure (including dynamic lifter) can be quite alkaline, and some suppliers are now adding lime to bagged cow manure and horse manure because some customers objected to the smell, (usually caused by nurseries leaving bags sitting in hot sun). And, only agricultural lime (calcium carbonate) should be used when liming is necessary as hydrated lime can burn plant roots and reduces nitrogen levels through conversion to ammonia.
When purchasing soil, always check the pH before adding fertilisers or lime to it, and always test the pH of your compost before adding it to the garden (well-made compost has a pH of around 6.0-6.5). If soil pH is not higher than 8, you can reduce the pH using elemental sulphur (according to the instructions on the pH kit) and dig into topsoil a 5cm layer of well-made compost, which will buffer plant roots from the unsuitable pH. Or, grow a legume as a green manure while waiting for the pH to reduce. Slash the legumes as they start to flower and dig them into the top 10 cm of soil. See Soil pH too high? , also Changing soil pH.
If the pH is higher than 8, it is not easy to reduce it with sulphur alone. As organic matter breaks down in soil it releases hydrogen ions that will replace the calcium ions in the soil, and gradually reduce the pH. Cow, horse or sheep manure (but not poultry manure) under mulch will also reduce the soil pH gradually as it breaks down. However, be very cautious where you source manures and mulch as more farmers are using herbicides that remain active in manures and mulch materials (except lucerne and pea straw) until they are broken down by soil bacteria. Test soil every 6 weeks after digging in the green manure, and you can use it for general vege growing when it gets below 7.5.
Recently, Anthea wrote to me about the problem of growing her Chinese Magnolia where soil is alkaline. I was just reading your article on changing soil ph and was hoping you could give me an idea on how to fix a problem I have with my magnolia x soulangeana. I bought the tree approx 4 years ago and, although it has grown well and has good leaf coverage, it has never flowered. My thoughts at first was that it was still too immature to do so, but I have since discovered that the ph level of our soil is very alkaline (we live on the side of an extinct volcano towards the coast). Over the last year, I have been trying to reduce the alkalinity of the soil with a general garden sulphur, but this does not seem to have worked. Once again, no flowers/sepals this year. I have checked the soil ph again, and it is still as alkaline as it was a year ago. I do not want to be as drastic as to uproot the tree and replant in an acidic base soil as I am aware that magnolias don’t take kindly to transplants but I am at a loss as to what else I could do. Do you have any suggestions as to how to rectify this problem? I live in Mount Gambier in the south east of SA. Any help/advice would be greatly appreciated.
It is a long job to reduce very alkaline soil with sulphur alone Anthea, and when soil is very alkaline plants can’t absorb the nutrients they need to produce flowers (or fruit, in suitable species).
I would try putting some aged cow or horse manure on the soil surface around the tree (keeping it well clear of the trunk) after a thorough watering, and covering the manure with about 5 cm of organic mulch to keep it damp. As the manure (and mulch) break down they will release hydrogen into the soil. The electrically charged hydrogen ions will replace the calcium ions in the soil and the pH will drop. It won’t happen overnight, but it will happen. One of the problems on dairy farms is that the soil becomes quite acidic due to the constant manure deposits.
Then, when the tree is in leaf, spray the foliage with organic seaweed extract diluted to weak black tea colour. Seaweed is high in potassium that plants require for good flower formation, and it also contains a range of trace elements that plants need but can’t absorb from alkaline soils. This may be enough to assist flowering next season. I would spray as soon as leaves form and again in early summer.
By the way, volcanic soils are usually rich in nutrients and Plants usually grow well in them when pH is adjusted. As the pH problem is likely to affect your entire garden, it might be worth your while to invest in a pH test kit and and make annual adjustments to your soil where necessary.
One of our SA readers wants to know what to do about the weeds that sprout from their horse manure pile, as she is concerned about spreading the weeds through her garden. She also has a problem with millipedes. Interestingly, manure and millipedes have a relationship because millipedes feed on decaying organic matter and they can lay their eggs in faecal matter. Millipedes are related to slaters. See Slaters and earwigs for controlling them in the garden.
Horse manure is often the easiest manure to obtain close to metropolitan areas. We have found horse manure to be a good source of plant nutrients and our miniature Shetland, Magic, works 24/7 to keep up supplies. Small amounts can be fermented in a bucket of water, then diluted, to produce a fertiliser tea for plants that need a boost.
But, adding uncomposted horse manure to the garden can encourage millipedes, slaters and earwigs. This is more common if you use sheet composting for the manure, a process of spreading a layer of manure on an unused garden bed, dampening it and covering it with mulch.
The best way to use fresh horse manure is to put it into the compost heap as it is a good source of nitrogen and generates a lot of heat, but there is a big difference between an active compost heap and a pile of horse manure. The manure should be mixed with dry ingredients such as straw, mulch, shredded newspapers, or dry leaves to create a good nitrogen to carbon balance. The heap should also be turned regularly to aerate the heap because aerobic bacteria require nitrogen, moisture and oxygen to work efficiently. When the compost heap is turned, newly germinated weed seeds get turned into the mixture and provide more organic matter for the bacteria to feed on. In its early stages, the heap should generate enough heat to kill off pathogens and seeds. As the composting process continues, the heap reduces in volume. As it gets cooler, you will occasionally see earwigs, slaters or millipedes in the mix but they are helping to break it down so don’t spray them with anything. When the organic matter reaches a favourable stage, earthworms move into the heap if it has contact with soil, and they digest the decomposing organic matter and turn it into worm castings. The final product, ready to be used on garden beds, is about one quarter of the volume of the original heap, friable, very dark brown in colour, and has a earthy, rainforest smell.
If you just leave horse manure in a pile to break down, it will tend to pack down and anaerobic (without oxygen) composting will occur. This is much slower, and can generate unpleasant smells. A lot of the nitrogen can be lost to the air and other nutrients can leach away when it rains.
To get horse manure to work even more quickly in a compost heap, tip it onto a hard surface and mince it a bit with the edge of a spade, because bacteria only work on the surface area of the ingredients. Producing more surface areas to feed on by chopping ingredients will greatly speed up the process.
I sometimes hear garden experts say that organic fertilisers are not as high in nutrients as chemical fertilisers, so you have to use more of them. This is simply not true.
The American Association for the Advancement of Science (AAAS) reported in February, 2009 that hundreds of studies have shown that “incrementally higher levels of fertilizer negatively impact the density of certain nutrients in harvested foodstuffs.” They also reported that the complex way in which nitrogen is absorbed in organic cultivation results in more efficient assimilation of the nutrient, allowing organically grown plants more energy to produce antioxidants, and the formation of less nitrates. Nitrates in food can form carcinogenic nitrosamines in the digestive tract. AAAS Conclusions
Excess use of nitrogen fertilisers (including uncomposted manures and manure teas) promotes bursts of soft, sappy growth that is much loved by chewing and sap-sucking garden pests. Overuse of a particular nutrient can block the absorption of other nutrients. Nitrogen and phosphorus compete for absorption. Overuse of chemical nitrogen fertilisers can also result in deficiency of the less mobile phosphorus.
Organic fertilisers don’t need to be as high in nutrients. Organic fertilisers made from a variety of recycled organic matter will contain a full range of major nutrients and trace elements. Organic fertilisers in the form of compost, castings from worm farms, animal manures, leaf mould, and broken down green manure crops and organic mulch add humus to soil, but chemical fertilisers do not.
Humus, the most stable form of organic matter, consists of electrically charged particles called ions. Nutrient elements also carry a weak electrical charge. Humus has a large surface area and many charged sites to hold nutrient elements through electrostatic force where they are easily accessible to plants, and regulate their absorption so that nutrients are not absorbed by plants in toxic quantities. Humus also provides a habitat for a group of beneficial fungi that assist nutrition in a wide range of perennial plant families. Some chemical fertilisers, such as superphosphate, suppress the activity of these fungi and other beneficial soil organisms.
Although clay particles in soil also carry an electrical charge and are capable of holding some nutrients, without humus in soil, phosphorus can become locked up with iron, manganese or aluminium, and unavailable to plants, and nitrogen and sulphur can leach from soil.
A suitable soil pH plays an important role in efficient absorption of a full range of nutrients. Adding extra fertiliser when soil is too acid or alkaline for particular species of plants will not help their growth. Humus in soil assists in maintaining a suitable pH. See:Changing soil pH
Although we tend to worry about plants getting enough fertiliser, fertiliser plays a relatively small, but essential, part in plant growth. The major contributors to plant energy are water and carbon dioxide. In the presence of sunlight, the green parts of plants can convert these into carbohydrates, which form the cell structure of plants. You could say, in fact, that plants are solar powered.