The pH level of soils is a key factor in the health of the plants. An improperly balanced soil can weaken a plant's growth and make it susceptible to a number of health problems. Oleander bushes grow best in soil that has a low acid content.
Learning the pH scale for soil testing is important for gardeners. The pH scale ranges from 0 to 14, with 7 being neutral. Soils with a pH of 0 to 6 are acidic, with lower numbers indicating a higher acid content. Numbers from 8 to 14 are basic or alkaline, with higher numbers indicating greater alkalinity. Oleander bushes grow best in soils with a pH of 5.0 to 7.
Managing Soil Acidity
Although oleander bushes need only a small amount of acid to grow, maintaining a steady pH will ensure the oleander bush stays healthy and produces blooms and leaves each year. A number of ways are available to add acidity to the soil if it has become too alkaline. Fertilisers with ammonium or urea make soil more acidic, as does decaying organic matter such as compost, according to the Clemson Cooperative Extension.
The type of soil in which an oleander is grown affects the pH over time. The kinds of rocks and organic matter from which the soil was formed are key in creating the pH level. Although oleanders grow well in a variety of soil types, those soils can change pH over time. Annual soil tests help gardeners maintain proper pH levels.
Water also affects the pH. Rainfall leaches out nutrients, fertilisers and chemicals, but acidic rain also contributes to the acid content. Heavy rains can dramatically alter the pH, leading to a greater need for fertilisers. Water the oleander bush at least once a week, but avoid over-watering to prevent pH changes.