Why is soil pH important?
Many gardeners may not be aware of how the pH of their soil can affect the growth and health of their plants. Without becoming too scientific, the pH (potential hydrogen) of your soil is a measure of how acidic or alkaline your soil is.
This balance affects the plant’s ability to access and benefit from nutrients which are present in the soil. In many instances, what appear to be signs of nutrient deficiency in plants (yellowing leaves, poor growth) can directly be attributed to an incorrect soil pH for that type of plant. Adding more fertiliser has no effect, as some nutrients become ‘locked up’ in the soil and not available to the plant.
Most plants prefer a near neutral soil, which has a pH of between 6.5 and 7. When the pH falls below this, conditions are said to be ‘acidic’ when above they are said to be ‘alkaline’.
How to test your soil’s pH
To test your soil pH you will need to take a teaspoons of soil from just below the surface of the soil in various parts of the garden bed you want to test. Mix this soil together and then take one teaspoon full and place it on the white plastic sheet from your testing kit. Add a few drops of the indicator liquid to form a paste. Sprinkle some of the Barium Sulphate on the paste and wait a minute or so. Hold the pH chart from your kit next to your sample and compare the colour to find your soil’s pH.
So how do you change your soil pH?
If your soil is a little on the acidic side, adding lime (either dolomite or garden lime) will raise the soil pH. It is best to do this a little at a time so as not to shock your plants and to prevent adding too much and making the soil too alkaline. Should your soil be alkaline, it is a little more difficult to fix the problem, but not impossible. One of the fastest ways is to add sulphur. However, adding sulphur can be a temporary fix. Adding lots of organic matter or compost tends to be helpful long term, particularly when sourced from things of a naturally acidic nature such as pine needles and sawdust.
An alternative to changing the pH of your soil is to grow the things that don’t mind a slightly high or low pH. Below are some examples:
Vegetables/fruit that tolerate acidic soils down to a pH 5.5
Apple, berries (strawberry, blueberry, currants, raspberry, gooseberry), carrot, cauliflower, chicory, corn, cucumber, garlic, melons, parsnip, peppers, pomegranate, potato, pumpkin, rhubarb, shallots, swede, tomato, turnip.
Vegetables/fruit that tolerates alkaline soils with a pH up to 7.5
Artichoke, asparagus, beans, beetroot, Brussels sprouts, cabbage, cauliflower, corn, currants (white and black), garlic, grapefruit, kale, leek, mulberry, nectarine, parsnip, peach, pear, plum, pumpkin, spinach, strawberries.