Besides controlling light and temperature, it’s also important to control the pH of a plant to ensure proper growth. The pH scale is a method of measuring acids and bases in a substance, ranging from 0 to 14. A substance with a pH reading of 7 or less is considered acidic, while a reading of 7 more is basic (alkaline). Neutral substances are those that have neither acidic nor basic pH readings. Just a one-point difference in pH can make a big change in plant soil. Although most plants thrive better in acidic soils, others prefer soils that are alkaline. For optimum growing, most plants need a soil that has a pH range from 5.8 to 7.0.
Nutrient Availability and pH Soil
The pH of a plant influences its growth in that it affects the availability of needed nutrients. A low pH can affect the soil’s ionic balance, such as clay destroying the soil’s structure. It can drain nutrients from the soil so they don’t reach plant roots. Soil pH also controls the solubility of nutrients and minerals that are needed for plants to grow. Solubility is important because fourteen of the seventeen plant nutrients that are necessary for plant growth are derived from soil solution.
The wrong pH in a soil can cause various plant diseases in that it hinders needed nutrients from being available because the soil isn’t healthy. For example, in conditions that are extremely alkaline, plant diseases such as potato scab and chlorosis of leaf vegetables can be a problem. Soils containing too much acid can cause diseases including brassicas and clubroot.
Improving Soil pH
Generally you can tell a soil’s pH by noting its colour. An alkaline soil (chalky) is dark green, while an acidic soil is yellow or orange. Bright green may indicate a neutral soil. However, it’s important to get an accurate pH reading rather than just guess. Soil pH test kits are used to test a soil’s pH. If a soil is found to be too acidic, it’s easy to add basic substances to cancel out some of the acidity by adding powdered limestone. On the other hand, soil that is too alkaline can be treated by including a substance such as manure that has more of an acidic pH.
The pH of the water or substance used to water a plant also needs consideration. Water, as it’s a neutral substance, is the usually best for growing plants. Whereas acidic water substances can eat away a plant, substances containing too much alkaline can be toxic. An example of how too much acid hurts plants can be seen in acid rain, a common weather condition in North America and Northern Europe where millions of plants and trees have been destroyed. Besides killing trees by acid from the rain seeping into roots and leaves fish and marine life have been killed in lakes because of acid rain.