There’s a reason people say “from the ground up” when talking about starting things. Because everything starts with the soil. Everything on this earth depends on the soil in some way. In particular, healthy soil. “What d’ya mean, healthy soil? “ I hear you say.
Soil can be many things: dead (dirt), poor (lacking in nutrients), sandy, clayey, loamy (mmm that’s the stuff), boney (another word for sandy but really means poor, old (like most of our soils in Australia – means it is lacking in nutrients as they have been baked and eroded away, silty, heavy (means clayey), water-logged (usually refers to clay content but can indicate poor drainage on a site), compacted, friable (used to be regarded as the be-all-end-all of cropping goals as it means it had been ploughed and is then fluffy and light for roots to easily penetrate. Now we realise we had that a little wrong and ploughing is now seen as destructive to soil health.) I could go on. We have also come to realise that if we don’t look after the soil we will be in some serious trouble: “The nation that destroys its soil destroys itself.”– Franklin D. Roosevelt – history is littered with failed civilisations who have treated their soil like dirt. Suffice it to say that it’s super important for a garden designer too.
What is soil?
Soil is a natural mixture of many ingredients. You can divide it into two categories: Living stuff and dead stuff. The main determinant of soil is the parent material -which means the geology from which it came and resides. Soils are formed from interactions of topography, climate, chemical interactions, biological interactions and time. There are resources online where you can research your soil type depending on where you are located.
Some systems break the soil down into two categories: biotic and abiotic or stuff that is or was alive vs non-living stuff like minerals and chemicals
The non-living (abiotic) stuff
Without getting too technical it belongs to these groups:
- Parent material which we can the ‘mineral content’ such as sand, clay, silt, stone, shells etc
- Organic matter – which is all the dead stuff such as plants (carbon) and animals
The Living (biotic) stuff
When you dig into the soil you will notice different colours and textures. These are usually in horizontal layers which we refer to as horizons.
Starting at the top with the “O” Horizons (O for Organic) the first layer isn’t soil at all but the stuff on top “O1” is leaf litter, bark, twigs etc. There should always be an O1 so that you can help protect and build what is below. The “O” horizon is the layer where the larger life is. It’s the interface between soil and air so everything needed for life is close at hand/claw/mandible/mouth etc It’s where everything is breaking down, crawling, and being turned over by the larger organisms and animals.
A Horizon This is also referred to as topsoil. If you have it, this is where you will find loam in one of its forms. Loam is the meeting point of sand, silt and clay in a ratio of 40%/40%/20% plus everything else (biotic and abiotic). Depending on the ratio as to whether it is sandy loam, loamy sand, loamy sandy clay… I could go on.
This is where the plants you grow are going to really get most of their goodies from as the roots are mainly in this horizon. It is rich in nutrients, minerals and the smaller aspects of life such as worms, microarthropods, fungi and the micro stuff. This is where you will find humus – the stable soil carbon resulting from composted and decayed organic matter. It’s the black stuff in the soil which acts as a sponge for water and nutrients so the more you have in your soil, the better your garden (and life) will be.
B Horizon (also referred to as subsoil) Heavier in weight and lighter in colour, this layer is usually clayey and less life as it is more compacted and has less air. Some roots will penetrate into this layer – mainly trees.
C Horizon This is the parent material or bedrock.
Of course, if you are in the metro area of a city, chances are your soil has been totally flipped upside down and messed about by the builders who built your house. We love builders, they’re lovely folks but not many of them understand soil and end up treating it like dirt rather than the foundation of life on earth. Why would they? I’m sure they don’t teach that at building school. The default opinion is “You garden guys come along and fix it later.” But once it’s flipped it’s not exactly like putting a puzzle back together. You can only do your best.
The best thing you can do when building a new house is to involve your landscape designer AT THE BEGINNING OF THE BUILD before ground is broken, not the end. That way they can brief the builders on what to do with your topsoil and levels when they start to excavate.
Testing Your Soil: It’s easier than you think
When I go to a new site to commence a design, one of the first things I do once engaged is to take some soil samples. Depending on the client brief and extent of work as to what I do with those samples.
If it’s an edible garden I will send some samples to the Vegesafe Program to test for heavy metals and contaminants as these toxins can be taken up by food crops and ingested by those eating their produce. The tests are free and it’s a really good idea to get your soil tested if you grow food in the metro areas or on land where you can’t account for its history and use.
If it’s a small job – like a planting plan or under $20K total budget I will do some basic tests, many of which are great to involve your kids:
PH -as easy as buying a kit from a hardware or nursery shop and following the instructions.)
I will then do some texture tests such as bolus and ribbon tests to start to figure out the components of the soil: clay, sand, silt, humus. Then you can add a decent sample to a jar and add water. Some call it a Mason Jar Test.
Then of course whilst taking samples I am looking for life. Because healthy soil is absolutely teeming with it. Not all of it is visible to the eye (such as nematodes, bacteria, archaea, protozoa, and some fungi) but a lot of it is such as the arthropods, earthworms and gastropods (snails and slugs) are. You can use several methods to gauge the levels of these in your soil should you wish and it’s particularly fun if you have kids. First whilst digging soil samples, lay down a tarp and put a shovelful of soil onto it. You want this to be to the depth of the shovel. You can also try building a Tullgren or Burlese Funnel for catching smaller (micro)arthropods and a simple trap for the arthropods such as a container dug into the soil so the lip is up to the level of the soil surface. You can release the critters once counted. If you have free-ranging chickens you probably won’t have a lot of arthropods but if you plan to pen them do a test before and then another at the same time the following year.
What you are wanting to determine is the health of your soil, how acidic it is, and what type it is (clay/sand/silt/loam). From here you can start to think about the kind of plants that thrive in these conditions whilst you slowly look to improve your soil.
You’re aiming for loamy soil either you live in an area where the soils are predominantly sandy, clayey or maybe silty. More on loam below.
Yeah, but WHY is biologically active soil good?
Basically, it’s about the circle of life. Is Elton John stuck in your head yet? Oops sorry.
So firstly the weather and bacteria and the fungi break down the parent materials (rocks and stones and other organic matter) then the protozoa and archaea eat the bacteria and fungi then the microarthropods eat them and so on. When something dies or poops it releases its nutrients and the plants take them up.
There are all sorts of cool things happening with fungi and their relationships with plants too. In fact, fungi are the stuff that really holds it all together in something they call the Wood Wide Web. Some fungi connect into the roots of plants (mycorrhiza) and have a symbiotic relationship whereby they exchange their minerals, water and nutrients they have mined from breaking down rocks and dead stuff and exchange those for plant sugars – they also carry chemical messages between the trees! It is estimated between 80-90% of all plants have fungal relationships. When we use heaps of synthetic fertilisers we interrupt this free food and message service that is happening between the plants and the fungi. We also let loose a whole lot of water-soluble nitrogen and phosphorus which then washes into the waterways and creates dead zones in the ocean. This is called eutrophication – too many nutrients feeding the wrong sort of bacteria which grows exponentially and uses up all the oxygen in the water and suffocates everything. Oops.
Not only that but synthetic nitrogen tends to burn carbon out of the soil and release it as a greenhouse gas. Carbon in the soil is vital for soil health as it is food for some organisms and acts as a sponge when it rains. Tillage and synthetic nitrogen combine to make some serious ecological problems but we aren’t here to talk about broadscale farming, are we? No, but let’s say that it’s OK to loosen your soils up a little and is good to ease compaction and get some organic matter deep into the profile but not to turn the whole lot over as you will lose loads of goodness and upset all the lovely relationships happening down there.
Healthy Soil = Healthy Plants = Less Work
The healthier your soil is the healthier your plants will be. (provided you have selected plants appropriate to your climate, soil and region.)
The healthier your plants are the less you will need to do to look after them. Plant pests and diseases usually occur from failing to meet the needs of the plant. There is no such thing as a black thumb or a green thumb just those who understand the basic needs of plants.
Another thing happens when we apply synthetic fertilisers – it’s the same as when we humans eat junk food- (we get fat, diabetes, heart conditions… you get the picture.) Plants growing on junk food put on sappy new growth that pests LOVE! Plants that grow naturally with a balanced level of nutrients put on firm new growth that pests find difficult to pierce and attack. As I mentioned earlier, if you have good fungal activity such as in the rhizosphere (root zone) the mycorrhiza will carry messages from plants being attacked by certain bugs which will signal to others to prepare for an attack by emitting phytochemicals to either deter those bugs or attract their predators. How cool is this stuff??!!
My advice is to let Mother Nature in and she will handle it. All we need to do is feed the soil what it needs. Carbon. Keep her covered as she dislikes being naked (weeds are basically her way of saying she needs some clothing so cover her with plants and mulch, add compost and manure if you need it.