Weekend Permaculture

This post looks at some of the ways we can test and categorise our soil from a pH perspective – just a drop in the ocean of factors that contribute to soil health…

Determining what kind of soil you have could help you determine what plants you grow or what approach you should take in terms of amendments if you are looking at planting a specific crop.

Soil pH affects how your plants absorb nutrients so it’s important to get this foundation right, for example

• Below pH 6.0, some nutrients, such as nitrogen, phosphorus, and potassium, are less available.
• When pH exceeds 7.5, iron, manganese, and phosphorus are less available.

What is pH?

The pH level is a scientific scale that measures the acidity or alkalinity of a substance, including soil. In chemistry, pH, also referred to as acidity, historically denotes “potential of hydrogen” ; it is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions are measured to have lower pH values than basic or alkaline solution.This scale ranges from 0-14 with 7 being neutral.

The ideal pH for most soil is between 5 and 7, as this will achieve the best potential for nutrient absorption.

Soil	Type	pH Level
Clay	Alkaline	Over 7
Loamy	Basic or Neutral	7
Sandy	Acidic	Under 7

Hydrangeas can be used as an indicator species for pH, however soil test kits are readily available and provide a much improved level of accuracy.

Clay Soil?

Our soil is modified clay. Most clay is highly alkaline with a pH level above 7. Many plants have trouble growing in clay soils because-

• clay has high water retention and poor drainage, and 
• the pH level is too high to allow for proper nutrient absorption.

Any soil above a pH of 7 is harder to remedy, however frequent green manure crops with deep roots will provide essential drainage and passage for worms to carry nutrients deep into the soil.   This as well as the added humus from green crops or a pH neutral compost is the best way to change the pH of your soil letting the biology do the work.

Adding small amounts of more acidic organic material which you can easily re-cycle like pine needles or oak leaves can help change the pH incrementally. Apply these either as a thin layer when you are green cropping (along with your carbon mulch from trees) or into your compost 

Our research on using ground coffee is not convincing, particularly ground coffee that has been brewed as the acidity is by-enlarge taken out of it at this point.

You will see powdered sulphur recommended however you really need to proceed with caution if using amendments like this, it is slow to change the pH (takes 3-6 months) and its antimicrobial properties mean that if you apply too much it can reduce the biodiversity in your soil.

The best advice we felt, was to know your soil and grow what works best in the soil you have.