pH adjustment is the first step in preparing to grow nursery crops. The correct pH level is necessary for a good nutritional environment for container and field grown nursery plants. pH has a dramatic influence on nutrient availability, the effects of toxic components like hydrogen and aluminum, and microbial activity. If pH is too low or too high, it can hamper cell production. For example, high soil pH indicates iron and manganese are less available. Low soil pH shows acid components, which stop root growth and nutrient absorption. Furthermore, proper pH is needed for microorganisms to convert compounds to forms used by plants.
As pH decreases, the soil becomes more acidic and can become toxic to plants. As pH increases, the soil is more basic and can block absorption of certain micronutrients, causing deficiency symptoms. Most nursery crops grow best in moderately acidic conditions- pH 5.5 to 6.0, but other nursery crops, such as azaleas and rhododendrons, need a lower pH range.
If the soil pH is too low, there are ways to correct it. Lime applications will neutralize acidity and raise pH. Dolomitic lime not only neutralizes the soil, but it also provides enough calcium and magnesium to support growth for the full growing period. Calcitic lime raises pH as well. It supplies calcium, but does not contain magnesium. Supplements of dolomitic and calcitic lime can only raise soil pH through liming- commercial fertilizers will not work.
Aluminum can be toxic to some plants if the pH is 5.5 or less. Nursery crops are often grown in mixtures of pine bark and sand. This media has little or no aluminum, so crops can safely grow at a pH level of 5.5. Azaleas and rhododendrons are more tolerant to aluminum than other nursery plants and can grow well in acidic soils.
Field-grown nursery plants require a higher pH than container-grown stock. Field stock grows better when the pH range is between 5.8 and 6.0.
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