Knowing the best time to provide your rhododendrons with fertilizer is incredibly important, as adding too much fertilizer at the wrong time can damage or kill your plants. Rhododendron plants have delicate root systems that hover near the surface of the soil. Adding fertilizer at the right time can ensure the roots take up the nutrients. Adding fertilizer at the wrong time can burn those roots. Following these tips can help you apply fertilizer at the right time.
If you're planting a new rhododendron, now is a great time to apply fertilizer. Look for fertilizer specially designed for acid-loving plants. Some fertilizers state that they're made for azaleas and rhododendrons. These are excellent fertilizers to use on your plants. Apply this fertilizer by mixing it directly into the dirt at the bottom of the hole you've dug for your new plant. If your new plant drops all its lower leaves after a week or two of planting, provide another application of fertilizer by sprinkling the product on the soil around the plant. Make sure your rhododendron is well hydrated before you apply fertilizer. Do not apply fertilizer to your plant if it is looking wilted or dehydrated, as you can burn the plant.
Existing rhododendrons appreciate a feeding with rhododendron food in May, when the buds on your plants are beginning to emerge. Look for rhododendron fertilizers that are labeled "slow release." This means they'll stay on the soil, providing food, over an extended period of time. Sprinkle the fertilizer around the base of the plant and water deeply. Unlike many other plants, your rhododendron likely won't need an application of granular fertilizer in the fall. Instead, apply a thick layer of dried manure around the base of your plant. This organic fertilizer will break down slowly and apply nutrients to your plant throughout the winter.