Soil pH

The pH of your soil is critical for your success in growing healthy plants, particularly food plants. For most vegetables, the ideal pH is around 6.4. At this pH, the minerals required by plants are most available.

There are a number of plants which require a pH level different to the 6.4 ideal. Blueberries are a classic example, generally disliking a pH over 5.5. Potatoes are also known to prefer a slightly more acidic soil.

 

Changing Soil pH

To change the pH of your soil, you want to use something that has a pH higher, or lower, than where you would like to end up. While there are products available on market that already have the correct/ideal pH, if you start applying them at the start of the pH changing exercise and your pH is significantly off the mark, it will take you a long time and many dollars to get where you want to end up.

A pH testing kit it essential, when thinking about modifying the pH of your soil.

 

Raising pH

Assuming that you are trying to reach a pH of around 6.4 and your pH is below that (say 5.5) the following products/materials will help achieve your goal:

  • dolomite (pH around 8 to 9)
  • wood ash (pH unknown, test it before you use it)
  • garden lime (pH higher than dolomite) - this can cause problems for the soil life, so only use it in extreme or special cases.
    NEVER use hydrated lime as it has an extremely high alkalinity which will likely cause harm to your garden.
  • gypsum (pH around 6.5) - it can also be used to raise pH if only minor adjustments are required (and the soil has a pH below 6.5)
  • compost - if you soil pH is quite low (e.g. 5), compost will help raise it overtime (composts are naturally acidic, but not highly acidic)

 

Lowering pH

The following products will help lower the soil pH:

  • sulphur (very low pH) - a little goes a long way. Also remember that it acts slowly, so give it about one to two months before retesting the soil pH and making further adjustments
  • gypsum (pH around 6.5) - it can also be used to lower pH if only minor adjustments are required (and the soil has a pH above 6.5)
  • compost - if you soil pH is quite high (e.g. 8), compost will help lower it (composts are naturally acidic, but not highly acidic)