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Composts & Manures

Plants are an expensive purchase and so it is important to make sure that the soil they are going into suits their needs so that they thrive and grow into healthy, beautiful specimens. Deciding how to prepare the area for planting and then maintain it to promote good growth is important and should actually be considered an investment.  We have said it before, that you can’t put a $10 plant into a $2 hole.

The number one rule to remember when planting most plants is to ensure that the soil is full of organic matter.  You probably hear this often and wonder what this is and why it is needed.

Organic matter refers to compost, animal manure and soil improvers that are made from decomposed living materials and are generally favoured as the best source of nutrients for plants.  They are important because they all are based on organic matter which brings in the earthworms and soil microbes that continue to turn over the soil, break it down and develop it into very rich growing soil.

In the vast areas with sandy soils throughout WA, organic matter is also essential in improving its water storing properties. The problem with sand is that each grain is a very uniform size and it is very easy for water to move quickly through it.  By adding organic matter to the soil, the water needs to twist and wind through big and small spaces slowing it down plus it gets held in the more porous organic particles which act a bit like a sponge.

For those with clay soil, the application of large quantities of gypsum to break up the clay is an absolute must but it is also the addition of organic matter which helps keep the clay from reforming into its hard, rock-type form in summer.

Compost is aerobically decomposed organic material which continues to have high levels of biological activity.  It is not high in essential nutrients so should not be counted on to fertilise the garden but it is its ability to help in the development of rich humus soil that is essential to a healthy garden.

To make compost, a combination of materials high in carbon such as paper and pine bark are mixed with green, high nitrogen materials such as mulched leaves and allowed to sit in great piles to heat up in the sun.  The process of heating encourages microbial activity which causes it to break down and compost.  Moisture is maintained in these piles and they are periodically turned to moderate the temperature and to allow oxygen into the centre so that the microbes remain alive.

Commercial composting uses a hot phase of between 55°C and 70°C for around 6 to 8 weeks to destroy weed seeds and unwanted micro-organisms whilst allowing the beneficial microbes to thrive.  This is followed by a cooling process to around 25°C for another 4 to 6 weeks.

Compost can be made at home but will also take many weeks.  For more information on how to do this, download the Better Pets and Gardens fact sheet called ‘Making Compost’.

When planning a new garden such as in a new subdivision where the soil has a low level of humus and is mostly sand, large quantities of compost should be mixed through all of the garden beds and even under the lawn.  Preferably do this before any planting begins to make the process much easier.  However, it needs to be remembered that it could take up to a year for the microbial life to move into these areas and continuous applications over subsequent years will be needed.

Established gardens which already have good source of humus will need lesser amounts dug through the top soil several times a year.  Compost has a cumulative benefit so that each season and every year the levels of organic matter in the soil will increase and so will the worms and the beneficial bacteria.  Sandy soils will need a lot more compost added than those with clay soils but in general, 5 to 10 centimetres spread over the surface and dug through several times a year is optimal but twice as much in a new vegetable garden.

Animal manure is simply that, manure from animals such as sheep, cows, chooks, horses and even pigs.  Any animal with a diet of grass or vegetable scraps will produce manure that is suitable for use in the garden but no two manures are the same, even amongst that from the same animal.

Manure sourced fresh from the farm gate is quite variable and differs a lot in the nutrients that it holds simply because the animals are all given different feeds.  This simply means that if using fresh manure it is important to keep an eye on the plants to ensure that there is no burning or that their leaves are not showing signs of yellowing which could indicate that they are missing a vital nutrient that wasn’t available in the manure.

The downside of using very fresh manure, apart from the smell and that the dog enjoys rolling in it, is that it can attract flies and even encourage them to breed in the garden.  In the metropolitan area, stable flies are a problem in areas where untreated poultry manure is used as these blood-sucking insects will attack both animals and humans.  This is somewhat reduced by restricting the application to times of the year with cold night time temperatures.

There is also a great deal of concern with using fresh manure in the vegetable garden. Although the plants thrive on it and leafy greens adore it, fresh manure can contain disease-causing bacteria which can contaminate vegetables such as E. coli.  Proper composting will kill these bacteria making it much safer to use on edible crops.  In the US, where fresh manure is used in or around growing vegetables that have edible parts that might contact the soil or receive water splash from rain or irrigation, the crop must not be harvested for 120 days.  In the case of sweet corn where the cob is not exposed to soil at all, the limit is still 90 days.

Commercially bagged manures are probably the safest and most stable method of purchasing animal manure.  It has been composted and aged to remove weed seeds and tested to ensure that it contains the right level of nutrients and trace elements and is much safer for used on edible crops.  Look for bagged manures that contain wetting agents as this is essential to making sure these products do their job as a water saving addition to the garden.

Cow and sheep manure tends to have a low level of nutrients because these animals graze on grass.  This makes it a terrific general purpose soil conditioner that can be used throughout the garden and, once composted will even suit Australian natives that are sensitive to phosphorous.

Chicken manure is very strong and extremely high in nitrogen.  It can be mixed with pea hay or sawdust to help to dilute it making it less likely to burn plants and because it is so high in phosphorous it should never be used on Australian natives such as banksias and grevilleas.  Chicken manure is very high in calcium because of the feed given to laying hens so it can be useful when trying to break up clay soils.

There is always a lot of debate over using fresh horse manure in the garden.  It is quite high in nutrient levels because of the supplements fed to horses so is a good tonic for flowering plants but manure collected from within stables contains a lot of urine which can burn any plant.  Horse manure also contains a high level of weed seeds because the animal’s stomach doesn’t fully digest these in the hay that they are fed.  Use horse manure with caution and where possible, compost it well before applying to the garden.

Blended manures offer a combination of several manures and are a great option as a general, all purpose organic product for the garden.

Both bagged manures and fresh manure can be made into a wonderful liquid manure or “tea” which can be used as a tonic for flowers and shrubs.  To do this, make a large tea bag by wrapping the manure inside several layers of cloth or hessian and tie it so that it hangs in a big bucket of water for several days.  Once steeped, dilute the liquid and apply it to the soil around the plants but not over the leaves.

When using manure, fork it into the top soil of the garden where leafy vegetables and annuals will quickly take it up through their roots.  Manure should never be left on the surface as the nitrogen will be lost as gas into the air plus it allows flies to breed in amongst the clumps and encourages the dog to eat it!

Commercially made composts which have been boosted with slow release fertiliser and wetting agents are often called ‘soil improvers’ or ‘soil conditioners’. These are an excellent option to consider since they have everything already in the bag making the job of planting just that little bit easier.  Soil improvers ensure that the plants get the nutrients that they need and that over time the soil becomes rich from microbial activity and effectively holds water.

Mushroom compost is a by-product produced as a result of manufacturing mushrooms in environmentally managed sites.  It is BFA certified as ‘organic’ and of course is a renewable resource.  It can be dug through the top soil as with other composts or used as mulch and is an excellent option as a soil improver.

Organic peat compost is also available and this can be used as a soil improver. Peat assists the garden soil to retain moisture and the beneficial microbes to make nutrients more available to plants.  It can be used in all existing and new garden beds including amongst Australian natives, azaleas and camellias.

When planting trees, shrubs and potted plants, dig the hole twice as large as the container and mix through one part soil improver to two parts soil before backfilling.  Water well and spread mulch over the top.

When buying and using manures, composts and even potting mixes, it is important to follow some simple hygiene rules.  Gloves are essential for handling manures and after the job is finished, wash your hands well and put work clothes straight into the washing machine.

Avoid inhaling the dust or liquid mists by wearing a mask to cover your nose and mouth.  After opening a bag, let it settle for a few minutes whilst going off to do another job and always ensure that the mixture inside is damp as this will also help settle the dust.

Store manures and compost in a cool, dry and well ventilated area and if it does spill, clean it up by vacuuming or wetting it first then sweeping.

Composts, manures and soil improvers should not be confused for potting mix.  They all have their different jobs and it is a waste of money to try to use them otherwise.  Potting mix, as the name suggests, is specifically formulated to have just the right amount of fertiliser, wetting agent and water holding ability to suit pots.  To use it in the garden to try to improve the soil is simply an expensive waste since the recipe to make it includes a portion of sand which is something that garden beds in WA just don’t need. Plus, the mix will get lost in amongst the soil and have very little benefit indeed.

Conversely, adding composts and manures to pots or mixing it with potting mix thinking that it will improve it is also throwing money down the drain – quite literally.  The nutrients in the compost and manure will simply wash through the soil and out of the base of the pot and that which is left will probably turn the potting mix sour meaning that it will have a bad stench and possibly cause root-rot diseases in the plant.

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