The chemical brothers…understanding acidity and alkalinity (pH)

Anyhow if you’re still with me, I’m hoping you’ll soon have a better understanding of pH in your soil and maybe even think  about regularly testing your own soil one day.

Back in 1909 in Denmark at the Carlsberg Laboratory the focus (believe it or not) wasn’t on beer.  A chemist called Peder Sorensen had discovered the importance of ‘potential hydrogen’ and thus pH was born.  I’m assuming he kept his findings in his awkwardly named Peder file.

I like to think Peder relaxed after his great discovery and had a quiet beer.

Mr Sorensen produced a logarithmic scale which starts at 0.0 and goes to 14.0.  Zero is the most acidic, while 14.0 is the most alkaline.  All importantly 7.0 is neutral and pretty much where we aim for with soil for our veggie patch.  Unlike a temperature or volume scale like most of us are used to, each step up or down on this scale is actually a ten fold increase.  To illustrate the power of this let’s say your soil pH is 6.0.  It means it’s 10 times more acidic than a pH of 7.0 but 100 times more acidic than a pH of 8.0!  So the take home message is your pH chart doesn’t work like the volume on an amplifier – small numerical changes are actually BIG!

In your soil, the pH has a huge influence on the availability of nutrients to your precious vegetables.  It seems crazy, but can keep pouring on phosphorus, but if you’re soil is too acidic, you’re plants can’t access it.  You can see by looking at the below chart that a sweet spot is between 6.5 and 7.5.

Testing your soil’s pH.

There are a couple of kits available in nurseries and hardware suppliers that cost less than $30 and will last for years.  In the kit you’ll find a colour card, a small bottle of liquid and some powder.  Take a sample of your soil and put it on a small plate.  Add the liquid to make a paste, then dust over with the powder.  Almost immediately you’ll see the soil turn a colour that you can match on the colour wheel to discover your soil’s pH.  As I’m doing a lot of pH testing for clients, my own garden and testing the Backyard Harvest bio-compost product, I’ve invested in a professional lab model which can be calibrated for ongoing accuracy.  This was several hundred dollars, so it may pay to see if cheaper hand held models are available.

How to change your soil’s pH.

Generally soils in productive gardens will need to be made more alkaline, however there is an exception in the case of blueberries and if you’re growing ornamentals then hydrangeas and azaleas also prefer acidic soil.

To raise soil pH (make more alkaline) we need to add calcium in the form of dolomite (calcium magnesium carbonate).

To lower soil pH (make more acidic) use elemental sulphur.  This stuff forms with the water in the soil and produces sulphuric acid which lowers the pH.

Having said that don’t forget to add compost, compost, compost!  Good quality compost has a neutral pH of around 7.0  Adding compost helps to bring either acidic or alkaline soil back to more veggie-friendly conditions by helping to make nutrients available to plant roots.

Different pH for different veggies?

As a broad principle, green leaf based veggies (spinach, lettuce, cabbage, kale etc.) prefer a pH in the more alkaline range, say 7.0 to 7.5.  Vegetables where the focus is on eating the fruit (tomatoes, capsicum, cucumbers, pumpkin) prefer a more slightly acidic soil around 6.0 to 6.8.  This helps to explain why tomatoes and pumpkins happily pop up in compost heaps where conditions are typically more acidic. Check out the below chart and promise yourself you’ll explore you soil’s pH this weekend!


Raise your pitchfork to the sky…

Well, I googled ‘compost definition’ and of the 2,290,000 results this seems to be the most popular.

“A mixture of decaying organic matter, as from leaves and manure, used to improve soil structure and provide nutrients.”   The word compost comes from the latin compositum which basically means a mixture of different things.

So unlike soil which is really the result of rocks being slowly ground down over huge amounts of time, compost contains lots of goodies that were alive and kicking just a short while ago so to speak.

As the definition suggests compost helps our soil structure which means it can hold sandy soils together while helping clay soils to break down…clever stuff huh!  It will also help to hold water in your soil, far more important than putting a layer of mulch over your patch and hoping for the best!

Another increasingly important reason to make sure your patch has regular compost added is because it increases soil biology/life.  What this means is that it makes major nutrients such as phosphorous, nitrogen and potassium available to plants.  That’s right, even if you keep adding fertilisers, if the soil has no life your plants can’t access it!  It’s another major reason for making sure you use organic methods that don’t upset soil life.

So now we know what compost is and why it’s so important, how do we make it?  There are basically two ways:

Anaerobic – this is also called cold compost, usually smellier (due to the methane produced) and harder to get the ‘right’ kind of bacteria involved.  This is a common method used currently by most Australians in the form of a static compost bin such as the famous Gedeye.  It’s been for as long as I can remember…check out the model’s clothes in the below picture if you don’t believe me!  You can greatly improve this type of compost by circulating the contents with a compost aerator.  Cold composting takes about 3 to 6 months to produce something you can use in the garden.

Aerobic – or hot compost uses a different type of bacteria which require air.  This means the compost needs to be turned every few days to oxygenate the pile.  Much faster, nicer to work with and the only kind I use.  The downside is you tend to need to have all ‘ingredients’ on hand to make it work well. Grass is almost the perfect balance of nitrogen and carbon and will break down without much help.  I usually add about 10% extra carbon material though to stop it forming into cow pats!  Hot composting produces compost in around 3 to 6 weeks!

Personally I tend to put most of my organic waste through chickens and worms leaving only grass clippings to be composted.  I currently use a tumble style compost bin which allows no way for rodents to enter the bin and produces compost faster than any other method I’ve tried.  This is especially important to note as normally a cubic metre (BIG) is required to get a hot compost pile going.

Smelly compost?

Main problem is too rich in nitrogen, which makes it too wet and hard to move, smelly etc.  Usually occurs because households produce far more ‘green’ waste than dry matter.  So add plenty of  straw, shredded paper etc. to keep the balance right.  A sprinkling of lime will also help to decrease the acidity and make things easier on your nostrils.

How to use your compost.

Compost is ready to work into your soil when it has a sweet smell, has cooled down (in the case of hot compost) and the ingredients are almost broken down.  Turn your compost into the top 20cm of your soil and leave for a week or so prior to planting new seedlings.  You can also ‘top dress’ garden beds with compost, especially over winter where it won’t dry out.

Green Manure

Now bare with me because I know this sounds like a kind of pointless exercise, I mean why grow something when you just dig it up again?  The thing is when it comes to growing food organically, our focus tends to be on the soil rather than just the plant.  So by planting out a green manure crop we’re really just ‘feeding the soil’ and making sure it’s in the best shape to deliver nutrition to our veggies.

By digging in your green manure it will add fertility, aid with soil structure and encourage earth worms to pay your garden bed a visit.  Plus with all that organic matter now in your soil, your revitalised veggie patch will be much better at holding water.

So what can you plant as ‘green manure’?  An old favourite is Lucerne – probably better known as alfa alfa.  Yes believe it or not those little sprouts that polarise culinary tastes in sandwich bars world-wide are the same seeds that grow into the most popular feed for horses and cattle on the planet.  Belonging to the legume family, lucerne will enrich the soil with nitrogen, but any other unwanted pea or bean seeds will also do the same.

Perhaps a more accessible seed to use is simply a mixed bird grain which you’ll find at any supermarket or pet food supplier.  For the beds I’m I’ve been using the grain mix I feed my chickens, plus adding any old pea and bean seeds that I’ve stumbled across so I get the advantage of nitrogen ‘fixing’ to the soil.   Just make sure you don’t accidentally sow a nice bed of kikuyu or other running grass or you’ll forever be stuck with it in your veggie patch!

Of course one of the other advantages of having something growing in a otherwise empty bed is that you’ll be less likely to suffer weed invasions.  Green manure crops can be planted very densely and grow vigorously making it a difficult for unwanted seeds to germinate.

So to give your vegetable beds the equivalent of long service leave, try planting a green manure crop this weekend and reap the rewards come spring time!

Why you just MUST have a worm farm Part 2

Here you can see the multiple tray system of my worm farm.

worm-farm web-1

Now I’m not allergic to dirt, but if feeding your worms becomes a messy ordeal then I reckon you pretty much won’t keep it up.  For this reason, my worm farm is located right near my front door.  It’s also an area that gets almost full shade in summer, helped along by the evergreen passionfruit climber which blocks the afternoon sun.  This means I have only two steps to get to my worm farm and it’s under cover so even on a cold and wet night I can make the pilgrimage in socks if necessary!

Just under the front of the worm farm is the drainage bucket to collect the FANTASTIC worm juice.  This model originally came with a tap, but I’ve removed it so the farm can drain free all the time and there’s no chance of the worms drowning.  The only downside is if you forget to empty the bucket regularly, you may find it overflowing.  This has never been a problem for me as the concrete slopes towards my passionfruit vine…in fact it may explain why I’ve had a bumper crop this year!

Okay now it’s time to look inside…

wormfarm 1st-tray-hessian-web

You can see I’ve used a hessian bag to cover the food scraps and to keep the moisture in.  Eventually the worms will eat through the hessian and it will be time to replace it – I picked this bag up from a local coffee roaster.  You could also use a thick slab of newspaper or one of the purpose built worm farm covers.  Feeding your worm farm can be a messy business so a feature I’ve really come to like is the self holding lid on this model.  It means you only have to lift the hessian and put the scraps under and can all be done with one hand.

Lifting the hessian you’ll see the scraps recently put down.  This is a fair amount, but after 12 months my worms will make light work of this in a few days.  Start with small amounts of scraps and if they’re still visible largely untouched in a week, you’re adding too much.

worm-farm 1st-tray-hessian-back-web

So now I’ve removed the top tray and you can really start to see the chocolate pudding-like worm castings.  There’s still a few worms in the top part of this tray as you can see.

wormfarm 2nd-tray-web

The 3rd tray reveals 10-15kg of prime soil conditioner made up entirely of kitchen scraps that would otherwise be rotting in our municipal tip.

wormfarm 3rd-tray-web

This one will be emptied shortly with the castings used for planting with my winter veggies (cabbage, broccoli and cauliflowers).  After that this tray will become the top feeding tray and on it goes!

In the very bottom of this worm farm is the base which collects and directs the worm juice to the outlet.  Note the raised section which allows the worms a dry place to rest if the more adventurous of the bunch find themselves down here…

wormfarm bottom-tray-web

Apart from feeding your worms, you need to make sure they remain moist at all times – especially during hot weather.  I use a normal watering can over the hessian – usually a litre of two of water a week.

wormfarm watering-web

This will start to fill your worm juice bucket.  Obviously the more water you put through the farm, the more diluted the juice will be.  Here I’ve used a litre of concentrated worm juice diluted with 8 litres of water to liquid feed fast growing asian greens and lettuce in my vertical wall garden.


Why you just MUST have a worm farm – Part 1

Worm castings or worm poo is pretty much the best soil conditioner you can get.  When added to soil before planting seedlings, or when included as you’re potting up a plant, you can be sure you’re adding a ph neutral chocolate-like substance that contains all sorts of goodies for your plants.  Perhaps of even more use is the worm ‘juice’ that results from the moist environment worms love to be in.  As plants can only take in nutrients in liquid form, this worm juice gives almost immediate results.


No photoshop tricks in this photo, those geraniums are really that red and the only fertiliser used on them since being planted a few years ago is worm juice!

So now you know how good worms can be for our garden, how do you best wrangle the little wrigglers?  Enter the worm farm…

Types of worm farms

In Australia we’re lucky to have a number of local manufacturers that produce quality worm farms that are designed for our conditions.  By ‘our conditions’ I mean they’re made from plastics that can stand our high levels of UV sunlight which we have an abundance of down under.  Some manufacturers also use recycled and/or recyclable plastics which is great to see.  Most worm farms have some form of ‘stack-ability’ which allows the worms to eventually leave their castings (or poo) and move onto areas in the farm where more food is available.  The main thing to keep in mind when looking at a worm farm is drainage and the capacity to easily access the precious castings.  Weight is also a consideration as these things get seriously heavy once filled with moist castings.  The model I’m currently using has a number of stackable trays, a drainage plug and a couple of other interesting features which I’ll cover in more detail.

In Part 2 I’ll demonstrate a flourishing worm farm in action and show you how your worm farm can become a non-stop fertiliser factory!