Azaleas, Rhododendrons and Blueberries
Each of these are acid-loving plants that will do well in Montana, when correct conditions are provided. Azaleas and rhododendrons are highly desired for their showy, colorful blossoms while blueberries are grown for their flavorful fruit. Care should be taken to ensure that you select cultivars that are adapted to your area.
Site selection and planting
The ability to grow any acid-loving plant depends greatly on the site selection and preparation.
Because of their shallow, fibrous root systems, azaleas, rhododendrons and blueberries require a soil that is uniformly moist, but not saturated. Organic soils are preferred while heavy, poorly drained soils should be avoided. Maintaining a uniform moisture supply can be accomplished with irrigation and/or mulching. Heavy, poorly drained soils will result in loss of plants to root rot.
Required pH level
In addition to the physical soil requirement azaleas, rhododendrons and blueberries require an acid soil with the pH in the range of 4.5 to 5.5 for best results. Soils that are more alkaline than the 5.5 will result in the plants not growing as well and becoming yellowish and more subject to winter injury. If your soil is too alkaline that addition of acid peat, sulfur or iron sulfate can lower the pH.
When planting it is important not to plant too deep. Roots of these acid-loving plants tend to be in the upper 4 to 6 inches of soil and need to be near the surface for aeration. To plant, dig a shallow hole deep enough to plant the top of the root ball at or slightly above the existing soil. Backfill around the plant with acid peat or a mixture of acid peat and the existing soil.
Mulching with acid peat, wood chips, sawdust, pine needles or similar materials to a depth of 3 to 5 inches is beneficial for controlling weeds, retaining moisture and adding organic matter. In addition, mulching will eliminate the need for cultivation which can cause injury to the shallow root systems. When using a sawdust mulch it is necessary to replace the nitrogen lost in the decomposition process by fertilizing with a high nitrogen fertilizer.
Once planted, azaleas, rhododendrons and blueberries benefit from the application of acid-forming fertilizers, such as ammonium sulfate, to maintain soil acidity and supply nutrients. Specially formulated fertilizers for acid-loving plants are also available and will be of great benefit. Fertilizers are best applied in the spring or early summer. In Montana there are no serious or common diseases or insect pests. Powdery mildew can sometimes cause azaleas to be unsightly in fall but it is seldom worth controlling with sprays. A bigger problem can be the damage caused by rabbits, field mice and other rodents during winter. A cylinder of hardware cloth around the trunk will help to prevent any damage.