Soil acidity and pH

spade in soilWhy is soil acidity and pH important?

Different soils have different dispositions. Soil can be acid, alkaline or neutral. Most plants prefer a soil with a neutral or slightly acidic pH level. The pH scale which measures soil acidity ranges from 1 to 14, with 7 being the mid-point. The mid-point of the pH scale is called neutral, and means that the liquid in the soil contains an equal amount of hydrogen and hydroxide ions.  As the number decreases, the soil becomes more acidic, and as the number rises, it becomes more alkaline.   

Most plants thrive with a pH level between 5.5 and 7.5. The optimal pH is usually between 6 and 6.5, so if your soil measures above or below this, it may be a good idea to do something to it to improve the nutritional uptake for your plants. At extreme values, below 3 or above 8, the soil becomes an inhospitable environment for plants. The nutrients in the soil cannot be absorbed; the structure of the soil changes and life cannot be supported.   

The vast majority of plants are co-operative enough and will be content even when the pH level of the soil isn’t quite right for them. But many plants will reward you handsomely if you adjust it.   

Optimum pH levels

Lush, healthy vegetable gardenHere are a few desirable pH ranges to strive for if you want to grow strong, healthy, productive plants.

  • Roses: 6.5 – 7.0 
  • Lawns: 6.0 – 6.5 
  • Potatoes: 5.5 – 6.5 
  • Leafy vegetables: 6.5 – 7.0 
  • Strawberries: 6.0 – 7.0 

How to measure and adjust the pH of your soil

It is possible, with some pH meters, to push the meter directly in the soil to obtain a pH reading. However, for a more accurate reading we would recommend following these simple steps.

  1. Take away the top layer of the soil, approx 1”. Break up and crumble the soil to a depth of about 6” depth. Take your soil sample from this layer of broken up soil. You will need about 200ml of soil. 
  2. Pour the soil into a large jar with a lid. Add distilled water and stir. You should use two parts water to one part soil. 
  3. Put the lid on and shake for at least 2 minutes.   
  4. Allow the soil to settle at the bottom for at least 10 minutes. 
  5. Dip your pH meter or litmus paper into the water above the layer of sediment at the bottom.   
  6. Read and make a note of the results. Repeat this test in several locations if you think the results may differ.  

Once you know the pH level of your soil, it’s easier to take the right steps to improve it.  Generally, you can achieve a well balanced soil by adding quality compost, like bokashi pre-compost.  Lime is a quick shortcut to a higher pH level.  If you need to quickly lower the pH level, you can mix in peat based compost.  Altering the pH of your soil takes time. Do not expect rapid changes.Instead, work steadily towards building the ideal soil conditions for your plants.

Does bokashi compost increase your soil acidity?

Bokashi pre-compost and bokashi tea are both acidic. The pH of the bokashi pre-compost and bokashi tea can be around 3-4; fairly acidic. This acidity elimates fruit flies, rodents and pathogens from the bokashi compost.

Many gardeners ask whether adding bokashi tea and bokashi pre-compost to their gardens will increase the acidity of the soil. In the short term, yes, the acidity of the soil adjacent to the bokashi pre-compost will rise slightly. However, the soil web will quickly work to neutralize the bokashi. Tests show that within a week or two of burying the bokashi, the soil pH neutralizes completely creating an ideal environment for your plants to thrive.

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4 thoughts on “Soil acidity and pH

  1. If you neutralize the pH of the bokashi tea or compost by adding lime or dolemite, is it safe to immediately apply directly to plants?

    1. The bokashi pre-compost is not finished compost, so needs to be finished in garden soil or a compost pile before being ready to be added to your garden. In theory, the bokashi tea could be neutralized using lime to bring the pH up. However, this is not something we have tried and there is a risk that the rapid change in pH would harm the microbes. We would recommend simply diluting the bokashi tea with water at a ratio of at least 1:100. Any excess tea can be poured down the drain; the bokashi microbes are very beneficial for blocked or slow drains.

  2. Hi there! I’m looking at adding acidity to my soil in order to plant blueberry. I thought I would achieve this by burying my compost waste and juice to the soil, but now I know that this won’t have a lasting effect as “within a week or two of burying the bokashi, the soil pH neutralizes completely”. If I buried my bokashi in soil inside a container (e.g. a big pot where I want to plant my blueberry bush), would it make any difference? Do you think the soil would remain more acidic for longer? Thank you.

    1. As you say, adding bokashi to your soil will help to raise the acidity in the short term. However, raising the acidity of garden soil can be hard to achieve in the long term. Rainwater and alkalines in the soil will, over time, neutralise the acidity. One of the best long term ways to increase your soil acidity is to add more organic matter. So, repeated application of bokashi and bokashi tea will help to raise acidity by adding organic matter and adding the acidity of the bokashi. However, these effects will be neutralised over time. Your suggestion of burying the bokashi in container for the blueberry bush will help to reduce the rate of neutralisation and keep the soil acidic for longer.

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