Food Forests, Part 3: Closing the Loop

Local legend around here has it that at some point in the past a guy by the colourful name of the “bush bandit” removed most of the topsoil from the land hereabouts and sold it off to householders in Melbourne for their gardens and lawns. Whether this story is true or not, I can only state for the record that when I purchased the block it had virtually no topsoil. The land had a hard baked clay pan with the strength of structural concrete where water would run off during heavy storms and any organic matter that did collect on top of that clay wouldn’t break down for years.

The wikipedia article for topsoil states that one inch (2.54 cm) of topsoil can take 500 years to form naturally. Now, I’m all for natural processes and am also fairly patient, but I don’t have the patience or time to wait 500 years. Also, most of the fruit trees that I want to grow — right here and now — have shallow to medium root systems which depend on that top soil.

This means that over the past seven years I’ve had to put a lot of thought, experimentation and activity into building top soil. Also, as I hate waste, I have implemented systems to ensure that anything, and I really mean anything, that gets brought onto the property and that was once alive or can otherwise be of benefit ends up in the soil.

Organic matter and minerals can come onto my property in a variety of forms including:

  • Food for humans, dogs and chickens;
  • Manure from humans, dogs and chickens;
  • Mulch and compost;
  • Rock crusher dust;
  • Field mice that are trapped and fed to the chickens;
  • Introduced plants and their soil;
  • Paper and cardboard; and
  • The manures of birds and animals that come onto the property from elsewhere.

The ultimate aim of collecting all of this organic matter and minerals is to build topsoil which improves overall soil fertility and allows me to grow healthy plants.

If I gave my green waste to the council to recycle, or was connected to the mains sewerage system, these nutrients would be lost from my property. By closing the nutrient loss loop it simply means ensuring that more top soil is built than is lost or utilised in growing plants. Once you are collecting more organic matter and minerals than you are losing from your property, you become a net importer of soil nutrients.

A simple guideline as to what plants require when building top soil is:

  • Vegetables require a soil made up of manure, some minerals, and mainly leafy green plant materials (ie. ex-vegetables and leafy green material) which is compost; and
  • Trees require a soil made up of some manure, some minerals, and mainly woody plant materials (ie. ex-trees) which is mulch.

To begin building top soil on my block, I realised that I needed a variety of the soil nutrients listed above. With the exception of human manure, I could simply add most of those soil nutrients onto the surface of the soil.

In building soil, I rarely dig, as I don’t wish to disturb the existing soil structure and it is just hard work. A lot of people involved in gardening and agriculture like to dig soil for some reason, but I’m not one of them. This may mean that in the application of soil nutrients to the surface, some small plants may get smothered, but experience has shown that they mostly tend to grow back.

Let’s talk about poo

At a time when food stuffs (and hence soil nutrients) are being shipped all over the planet and fuel costs are increasing, we need to begin thinking about a local resource that we all have access to, but has a very high yuk factor — human excrement.

Fortunately for me, my house is not connected to any mains sewerage services, so I had several choices about how my household human wastes (black and grey water) could be dealt with. In the end I chose a worm farm system which takes all of the human wastes from the household and processes them in a worm farm. This system produces treated water, worm tea and vermicast (worm poo), all of which are released into an 200m2 herbage pasture.

The worm farm is gravity fed so it requires no additional inputs of energy, and it quietly goes about its job of turning human wastes into soil nutrients.

The herbage pasture stays green even over the hottest summers and is for the benefit of the local wildlife (kangaroos, wallabies and wombats) which in turn keep the pasture cut down, bring in all sorts of seeds and spread their scats (poo) throughout the rest of the food forest, thus spreading soil nutrients randomly about the place.

It’s a real dilemma for me when I’m at another location, having dinner, visiting friends etc. Do I hang on, or go there, knowing that some soil fertility is lost to my systems?
Most urban areas process human wastes using centralised local treatment plants, most of which ends up in the ocean. Not only do they use quite a bit of energy in the processing, but sometimes during floods they can release untreated human wastes into local creeks, rivers and eventually into the ocean. Given how quickly top soils are being depleted worldwide in the production of food for humans, animal feeds and biofuels, wouldn’t it be great if some of our human wastes were composted and converted back into topsoil to assist with future food production?

Mulches and compost

I really enjoy bringing either composted woody mulch (mostly) or compost (occasionally) onto the property and spreading it around by hand and wheelbarrow. With over 300 fruit trees, a number of vegetable beds and a deep mulch litter system for the chicken run, my place eats mulch! Spreading mulch and compost around really means either placing it at the bottom of fruit trees out to their drip lines or throwing it around so that you get a thin, random top coating which disappears down into the soil over a few weeks.

Heavily mulched cottage garden

In Australia, mulch and compost are treated as waste. Local governments in urban areas collect green waste from householders, chip them, compost them and produce mulch and/or compost (or a combination of the two). These are then delivered in bulk to sand and soil suppliers who on-sell them to the public. Sometimes, a council has so much of these materials that you can purchase directly from them at reduced prices.

Over the past 7 years I have probably brought about 200m3 (about 7,063ft3) of mulch or compost and spread it around the place.

Mulch and its water holding capacity

Green manure crops

Another method that I use to build top soil is to plant green manure crops. These green manure crops extract nitrogen from the air and the nitrogen is then stored in the soil as nodules on the plants roots with the help of beneficial bacteria. Once the plant dies off or is somehow removed, the nitrogen becomes available to soil flora and fauna and as a fertiliser to other plants. The leaves and branches of these plants can be used as mulch too.

Green manure crops, pea and vetch, as ground cover

Some people dig those green manure plants into the top soil, however not wanting to dig anywhere if I can help it, I simply let them go to seed, die back and then mow them. I’ve found here that they readily self-seed and you’ll get a larger crop of the same plants the following year.

There are quite a lot of green manure crops to select from. In my food forest, I grow a mix of vetch and sweet pea in places and they grow very well together.

There can also be quite long lived nitrogen fixing plants too. I also grow around the perimeter of the food forest, many acacia melanoxylon (Blackwood) and tagasaste (Tree Lucerne).

Three year old blackwoods

Concentrate on growing rather than killing plants

Some people get very fixated by weeds. Even worse, sometimes they start telling me about some glyphosate based herbicide which would be just perfect for despatching my weeds. Wouldn’t it be far better for the soil if those same people put their energy into growing plants rather than trying to kill them?

Years ago, I read Peter Andrews book, “Back from the brink – How Australia’s landscape can be saved”. His ideas were simple, yet very effective:

  • Store water in the soil rather than letting it flow across the surface, and if it does, slow its progress so that it starts to infiltrate the soil;
  • Allow weeds to grow for a season rather than spraying them with herbicide (or digging and exposing the top soil to the sun) and then slash / mow them so they become part of a mulch which starts or enhances the building of top soil (this is called ‘chop and drop’); and
  • Encourage nitrogen fixing trees or deciduous trees (particularly willows along creek beds) which drop leaf matter during the cooler months. Leaf matter is a form of mulch which also starts or enhances the building of top soil.

The last point is particularly applicable to Australian conditions, because in most parts of the continent, native trees will grow for most of the year depending on water availability. Yet, it is during the warmer, drier months of summer that eucalyptus trees drop their leaves due to water stress. Those leaves are usually already dry because of the summer heat which adds to the fire fuel loads on forest floors. In addition to this, their dryness and high oil content means that it can take several years before the soil flora and fauna have broken these leaves down into top soil.

Here, I let a huge diversity of plants get a chance to grow and seed as a ground cover (herbage). About twice a year (Spring and Autumn), I mow the entire ground cover using a small Honda push mower on a medium height setting. The mower tends to mulch all of the plants and the results fall where they will. As well as providing mulch to the surface of the soil, the plants that have been cut with the mower, self-trim their roots below the soil surface which provides further organic matter and enhances the soil building process. After a few years of this process, the ground cover plants tend to grow back quicker and healthier than previous seasons.


To grow, every plant requires its own unique and individual requirements from soil.

In ecology, there is a concept (Liebig’s law of the minimum) that states that growth in a system is ultimately limited to the scarcest nutrient. For example, Australian soils are generally accepted to be phosphorus deficient. As phosphorus is essential for the growth of commercial crops (among most other plants), then it is a serious limitation to the growing of commercial crops in this country.

A monoculture farm would eventually deplete some element or mineral and this will be evidenced by declining yields. Most large-scale monoculture farms generally bring in fertilisers to apply to their crops, yet plants don’t simply require NPK (nitrogen, potassium and phosphate) to grow. As well as those soil nutrients, plants can also require: boron; calcium; cobalt; copper; iron; manganese; molybdenum; sulphur; and zinc, to name just a few. Once one of these necessary nutrients has been depleted for a particular plant, Liebig’s law kicks in and yields are reduced and/or the nutrient density of the particular plant declines.

I’m unsure if a large scale monoculture farm, even if farmed on an organic basis (ie. no fertilisers, herbicides, fungicides or pesticides), could be sustainable. Only a polyculture agricultural system with nutrient inputs and outputs like a food forest can hope to avoid this limitation.

Animal systems

A wombat enjoying the herbage

In commercial agriculture, animal systems are not usually combined with plant systems as growers tend to specialise in particular areas because of commercial necessity, however, with a small scale food forest both systems can be combined.

Here, I have chickens, and apart from their entertainment value, they also provide eggs, pest control and manure. The best outcome for both the chickens and the food forest would be for the chickens to be able to freely roam all day throughout the food forest. However, it is a difficult life for a chicken here because of the number and variety of predators (eg: foxes, eagles, owls, dogs, etc.) day and night who would love nothing more than to dine on a juicy organically fed chicken.

The chickens here do live in a fully enclosed shed and sealed chicken run but they free roam through the food forest for an hour or two per day under supervision. Living in an enclosed chicken run means that their manure must be removed regularly otherwise the health of the chickens will quickly suffer. I mentioned previously that I bring in composted woody mulch as a soil additive. Some of this woody mulch is added to the chicken run as a deep litter system. The chickens will, over a week, scratch and turn over the woody mulch and also excrete into it which adds nitrogen (amongst other nutrients) to the woody mulch material. It is then removed from the chicken run and applied to any area of the property that requires it and new woody mulch material is brought into the chicken run.

The author spreading chook-processed mulch about the emerging food forest

Animal systems don’t have to be hard work or cost you anything either. Over summer, I always ensure that there is water available in a secure spot above ground for the native birds in the area and I now have families of magpies, kookaburras and eastern rosellas amongst other larger and smaller birds living in and around the food forest. These same birds also scratch through the ground cover, eating pests and spreading manure and seeds about the place. Most native birds here aren’t interested in the fruit (except for cherries and berries) and only tend to eat the fruit if they are thirsty.

Animal systems don’t have to look like cows grazing in a fenced paddock either. As the food forest is located within a larger native forest, I tend to get a lot of animals browsing through the food forest. The herbage previously mentioned is provided for their benefit and most nights kangaroos, wallabies and/or wombats will be grazing in this area. Not only do their activities reduce the need to regularly mow the herbage / ground cover, but they also spread their manure through the food forest and surrounding forest for the benefit of the soil at no expense or effort to myself.

Mum, joey and adolescent kangaroos enjoying the herbage


Recently, I had to dig a hole to place a post for a climbing frame for kiwi fruit and received a pleasant surprise. After 7 years, the photo below shows the results of all of this soil building work here. The hole was about 500mm (about 20 inches) deep and you can clearly see that between the measurements of 300mm (about 12 inches) and the top of the hole at 500mm (20 inches) was topsoil, where previously there was none!