Rhododendrons and azaleas love acidic soil. Unfortunately, the soil in southern Ohio is very alkaline so the acidity must be increased before rhododendrons and azaleas will really thrive. To do this you can add peat to the soil.
1. Mix a liberal quantity of baled peat (Canadian, Dutch, German, or Swedish) with the soil in the bed. Peat sold in bulk is usually not satisfactory. Thoroughly soak the peat before mixing with the soil. Dry peat takes moisture from the newly planted material.
2. Use ½ peat and ½ soil (thoroughly mixed) and add 1 cup of “Flowers of Sulfur” or “Aluminum Sulphate” for each bushel of soil mixture.
3. When planting, entirely remove the burlap from the earth balls about the plants and see that there are no large lumps of soil to form air pockets under or around the plant. The top of the ball should be level with the bed. Care should be taken not to get the plant too deep. Flood the bed well with water to settle the soil. Never pack soil about the roots. Be sure to remove all nursery labels and wires.
Rhododendrons and azaleas make handsome additions to foundation plantings. They do best in our locality when used on north and east exposures. They are also ideal for naturalistic plantings in wooded areas. Do not plant either rhododendrons or azaleas in a location where they will get an extreme amount of whipping from winter wind or where the summer sun reflects intense heat from buildings or pavements.
Rhododendrons and azaleas have shallow, fine root systems and are easily damaged by dry spells. Consistent watering during droughts is necessary. Watering in the summer and fall helps prevent winter injury. The flower buds also benefit from this watering as they are formed about this time.
Plantings put in after September, and some of the tender varieties, will benefit from evergreen branches (such as discarded Christmas tree) laid over the roots and worked in among the branches of the plant. It is normal for rhododendron leaves to curl when the weather is below freezing.
Brown specks on the underside of the leaves are generally caused by Lace Wing Flies. They are easily controlled by spraying with “Isotox,” “Malathion,” or “Orthene” used in accordance with the manufacturer’s recommendations.
It is important to fertilize rhododendrons and azaleas twice a year with a product specifically for acid loving plants. Care should be taken to use fertilizers in accordance with the manufacturer’s recommendations to avoid over-feeding and possible injury to your plants.