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Understanding pH levels in your soil

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In previous blog posts I mention testing your soil which can be done with a simple kit bought from any good gardening nursery. The Kit is a pH soil test kit and should be used by all gardeners so you can ensure your soil is at the correct level. Your pour blood sweat and tears into your garden so it makes sense to ensure the soil has the right amounts of nutrients - let mother nature work for you.

Soils in the Top End sadly are quite poor in condition, I get jealous when I head south and feel the soil but a challenge is what I love and the tropics give me my fair share in gardening. What i battle is the wet season, as much as I love a good rain its the big down pours that leach all my nutrients out the soil which annoys me.

For new comers to testing firstly what is pH? Well pH stands for potential Hydrogen and the kits mentioned will test to see how acidic or alkaline your soil is. Most plants will prefer neutral soil which is around 6 but can vary slightly depending on which kit your using. Some plants do like to have acidic soils such as azaleas and camelias however there isn't to many plants that will thrive in alkaline soil.  Here in the Top End I find most soils are acidic a reading of 6 and below is common for first testing in most gardens I work on.

What causes our Top End soils to become acidic?

According to the research done our top influence up here is 

  • Rain- Our storms have a pH of 3.0 which is strongly acidic
  • Decomposing organic matter releasing organic acids
  • Chemical fertilisers most are quite acidic

So you have tested your soil and can see its lacking in nutrients and now you want to fix the problem but what? Below is a slight touch on a few nutrients i tend to use. From what i have learnt over the years is this:-

Soils on the acidic side:- Add dolomite lime at a rate of about 100gm/ m 2 2-3 times over a few months as trying to correct the balance in the one hit will cause shock to your plants.

Soils on the alkaline side:- A bit harder to treat but to get started try adding sulphur 25-50gm/ m 2 then start building the soil with organic matter. Up here in the tropics of the NT I have never come across a reading that has been too high in alkaline so gladly I have not had the pleasure of correcting this as yet.   


How this helps? Used as a soil conditioner Gypsum improves structure to soil helping with drainage mainly with heavy clay like soils. Gypsum is commonly known as a clay breaker and sold as such, I tend to use gypsum when preparing a garden bed then don't really tend to use it again for a few years as its quite long lasting. If using gypsum always water it well in so the ground really soaks it all up and only minimal traces can be seen to the eye.

Seaweed Solutions

How this helps? Most mixes have anywhere between 50-70 minerals and trace elements added to improve soil structure but remember this is not a fertiliser as many tend to think. Most mixes will contain Mannitol and Alginic which acidify the soil helping your plants to absorb the nutrients.  Using a solution will play a significant role in your gardens ability to fight fungi and disease.  You will find stronger crops, better flowing and an increased sugar content in your fruits as well. I use a seaweed solution when transplanting as it reduces shock due and promotes root growth.  I fill a watering can up and put in a few tablespoons in when using- always dilute.

Lime / Dolomite Lime

How this helps? Used as a soil conditioner by adding calcium carbonate which will neutralise soil acidity. I don't use this with any fresh manures as lime tends to release ammonia gas which is quite harming to your roots. Dolomite contains calcium magnesium carbonate which is also used as a soil conditioner and will also react with fresh manure releasing harmful gas.

Iron Sulphate

How can this help? Used as a soil conditioner, will add iron to the soil which is used to neutralise soil alkalinity.

Powder Sulphur

How can this help? Soil conditioner by adding sulphur into the soil which neutralises soil alkalinity.

Chicken Manure

How can this help? My favourite of all soil conditioner's, chicken manure will add nitrogen, potassium, ulphur, iron, zinc, phosphorous, calcium, copper, boron, molybdbenum and maganese to your soil. Don't ever use chicken manure direct, let it sit and weather for a few months otherwise it will burn your plants roots.

Green Manures

How can this help? Green manures increase the organic status of your soil, reduce soil erosion and will help the soil retain your added minerals. Nitrogen rich organic materials help break up compacted soils, smother weeds and provides habitat for all those beneficial insects. If your into veggie gardening you might be familiar with crop rotation many will use a green manure cover crop especially through the wet season. If your wanting to do this try buckwheat, cowpea, Japanese millet, lablab, mung bean or soy bean. Though the wet season i will write an article on using cover crops as I find them to be so beneficial yet not used enough in the home gardens. As a commercial gardener I'm always down at the local dump and the amount of green waste I see in trailers amazes me, all that can be used as compost adding nutrients into the soil please if your one of them save it. I bet you spend money every year buying fertilisers and hay bales yet what you throw out works better if its put to good use.   

Blood & Bone

How Can this help? A well known and used product on the market with its great mix of nitrogen, phosphorous and calcium. Nutrients all leak slowly supplying your plants with a steady intake of goodness. A little trick I like to use is composting my banana leaves with hay then adding the mix to my blood and bone mixture as you will find blood and bone hasn't any potassium so adding the organic mix just gives it the perfect portion of the missing element.  

Trace Elements

How can this help? Adds all types of minerals such as sulphur, zinc, boron, copper, magnesium, calcium & molybdenum which as are essential for the biochemical process but not used right can be quite toxic to your plants. 

Mushroom Compost

How can this help? Soil conditioner, mushroom compost is made from poultry manure and hay however I find brands can differ some will be quite alkaline whilst others acidic. So i would probably check this out if your using it on plants especially acid loving plants, a pH test kit will give you an accurate reading.

Rock Dust

How can this help? All rocks have mineral elements so applying rock dust is a way of introducing these elements without waiting years upon years for the weather to break down your rocks. The elements you will benefit from are silica, calcium, magnesium, iron and potash. When choosing rock dust the finer the dust is the faster the nutrients will be released with basalt and granite being the richest. Use your rock dust in conjunction with your normal composting routine, I like to scatter a few handfuls on my soil before laying down my composting layers.  

 Human Waste

The most unpopular of all I'm not promoting you rush out to the garden to relive yourself but yes urine is sterile and can be safely used if diluted 10:1. When your having your next BBQ and your men wander into the garden for sprinkle demand they take a bucket of water to dilute Smile    


If the above is still a bit confusing remember most garden nurseries are more than happy to help and full of information, the testing kit is simple to use so once you have your reading simple ring or email them and ask for advice. We are always here as well sending an email to us at This email address is being protected from spambots. You need JavaScript enabled to view it. with as much information as you can and we can also help you out.

Note: This article will be updated throughout the year.


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©Kylie Stephens- Lawn Ranger
in Gardening Hits: 298049
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Guest Monday, 18 February 2019