Did you know that some plants prefer acidic or “sour “soil and other love ‘’sweet” or alkaline soils? In this article we will be focusing on acid loving plants and explain the difference between acid and alkaline soils.
First let me explain what acidic or alkaline means and how it is measured.
The measure pH (power of hydrogen) is used on a scale from 0-14 to indicate how sweet or acidic soil is. Before we get to scientific, just remember that a pH7 is neutral, anything above is alkaline (pH8) and anything below is acidic (pH6). If the pH goes too high or too low certain elements in the soil becomes unavailable to our plants and will cause nutrient deficiencies. Although most plants grow very happily in soil with a pH7 – pH8 there are some exceptions that need acidic soil with a pH6 or even lower. These are plants like Azalea, Rhododendron, Camellia, Zantedeschia, Brunfelsia, Gardenia and Hydrangeas of which the latter’s colors can be manipulated by raising or lowering the pH of the soil. Blueberries and roses also appreciate acidic soil.
It is much more difficult to lower the pH of soil than it is to raise it. A few natural ways are to use your discarded coffee grounds, Oak leaves, or Pine needles. Layer these on top of the soil and do not dig them in as it will rob the soil of nitrogen once it starts decomposing. This must be applied to the soil on a regular basis as soil tends to revert back to pH7 or neutral. Should you not have these items readily available or save yourself the hassle of collecting it, you can always go to your local garden center and purchase a couple of bags of Acid Compost. The pH of Acid Compost can vary from pH5 to just slightly acidic pH6.5 or more depending on the materials used for the manufacturing thereof.
For new flower beds you can just add the Acid Compost on top of the soil and dig it in. For existing beds, put a layer of Acid Compost between the plants as a mulch. When you water the plants the acidity of the Acid Compost will move into the lower layers of the soil with the water. Remember to add Acid Compost to your beds regularly, at least once a year to maintain a low pH level. If you are going to pot up one of the above-mentioned plants, you may use the Acid Compost as a potting soil straight from the bag. Remember to mix in the appropriate organic fertilizers to the Acid Compost before planting.
Do not use “bluing agents” like Aluminium Sulphate, the effects are very sudden, and an overdose can lead to toxic levels of aluminium in the soil. Ferrous Sulphate or Iron Sulphate can interfere with the phosphorus levels in the soil. Synthetic fertilizers contain ammonium nitrate or ammonium sulfate and have an acidifying effect on soil, but the manufacturing of these products contributes greatly to CO2 emissions and should be avoided if possible. Sphagnum Peat may also be used to lower the pH of soil but bear in mind that it is not a renewable resource.
It is always better if we can let nature take it own way and if we really must amend the pH of soil, rather consider planting your acid loving plants in raised beds or containers. It will be much easier controlling the pH. There are no “quick fixes” for pH and doing it organically is a slow process and may take a long time to achieve the desired results, worth the wait.