Soil pH is the level of acidity or alkalinity of soil. The acidity of soils depend on their composition and particularly the level of Lime (calcium) within it.
It is important to know the pH level of your soil because it will tell you which plants will grow in it and which won’t. As mentioned above testing soil pH can be a job for the professionals. It can also be carried out by you though, using a soil pH tester.
Testing soil pH for yourself will usually involve adding a drop of solution to your soil sample, waiting a little while for it to settle, and then comparing the resulting colour with a chart. All the equipment and information you need will come with a decent quality soil pH tester. Please click Soil testers UK for a soil pH tester in the UK and on soil testers US for the US.
Soil pH levels are measured on a scale of 1-14. Acidity is at the lower end, alkalinity at the top, with 7 being neutral. Some plants prefer a more acidic soil (less Lime) while others need an alkaline soil.
Examples:
* Potatoes, Broad Beans, Cucumber and Parsnips grow best at a pH level of 5.25 - 6, a more acid than alkaline soil.
* Cauliflower, Leek, Celery and Lettuce thrive best in soil pH levels of around 7.5, less acidic.
Changing your soil pH levels
If after using your soil pH tester you find you have a soil pH level of 5.5, but have set your heart on growing Cauliflowers, then you need to add lime (organically produced of course!). Doing so will raise the pH level of your soil and make it more amenable to Cauliflower and other vegetables of a similar pH level preference.
Lowering soil pH levels makes the soil more acidic. This can be achieved by adding organic compost or manure to the soil. For an extensive guide to pH vegetable plant preferences please click on vegetable pH preference guide.
I would just like to add something concerning lime. A lack of it in your soil (a low soil pH level) will prevent optimum growth in many different types of plant. It is generally accepted that a pH level of 6.5 is the preferred level for most plants.
Lime also helps some soil types, especially clay, with water drainage and aeration, and encourages the presence of worms (great boosters of fertility and nutrition) in the soil. It manages these improvements by producing larger particles which create the space mentioned above.
However, not all plants tolerate higher soil pH levels. When planning your organic vegetable garden please take this into account and become acquainted with vegetable pH preferences.
There is a great alternative to changing soil pH levels of existing soil and/or growing only certain vegetables though. This is called ‘raised bed gardening’. Click on raised bed organic gardening to learn the benefits and how to do it.