You can illuminate shady areas of your garden with the vibrant flowers and evergreen foliage of rhododendrons. Rhododendrons are frequently hailed as shade-loving shrubs; however, it would be a mistake to assume that all rhododendrons will grow well and produce abundant flowers in full shade. Many many varieties will not flourish under heavily shaded conditions. However, with preparation and planning, you can grow rhododendrons even in full shade.
Prepare the soil in the shady area that you have selected. Rhododendrons prefer well-drained, nutrient-rich acidic soils with a pH level between 5 and 5.5. Test your soil to determine the most suitable action to amend the soil. According to Missouri State University's Extension Service, agricultural sulphur and iron sulphate are effective in lowering the soil's pH and increasing acidity. Mix organic materials such as ground pine bark, sand and topsoil into the soil---this enriches the nutrients and enhances the soil's drainage. The ratio of organic material to soil should be roughly 50-50.
Buy a rhododendron variety that can withstand full shade. Most rhododendrons flourish in partial shade but can become spindly and exhibit minimal flowers in full shade. Varieties such as Catawba rhododendron, however, will brighten partially to fully shaded areas of the garden with vibrant blooms and evergreen foliage.
Dig a hole in the prepared area that is slightly larger and equally deep as the container that holds the young rhododendron. Remove the plant from the container and set the root ball in the hole, ensuring that it rests approximately 2 inches higher than the soil surrounding it. Fill the hole with your planting mixture and water thoroughly.
Water your rhododendron a minimum of twice per week. The shrub forms its roots near the surface and can easily dry out. According to Ohio State University, rhododendrons require a minimum of 1 inch of water per week. Soil should be kept moist but not wet or soggy.
Add a 2-to-6-inch layer of mulch around the newly planted rhododendron. If you are using hardwood chips or sawdust, 2 inches is sufficient. If you are using oak leaves or pine needles, you will need approximately 4 to 6 inches.
Soil testing kits are available online and from local nurseries. If your pH is 7.5, add 2.27 Kilogram of sulphur or 5.22 Kilogram of iron sulphate for every 100 square feet. If your pH is 6.5, add 6.8 Kilogram of sulphur or 1.36 Kilogram of iron sulphate for every 100 square feet. Conversely, if your soil is too acidic (pH levels of 4.5 or lower), you may need to add ground limestone to the soil to raise the pH level.