Fertilize azaleas and rhododendrons sparingly and only when flower buds swell in the early spring, even if they are fall bloomers. Heavy applications of fertilizer will burn the plants. Water plants during the summer if rainfall is less than 1 inch per week.Click to see full answer. In this regard, what is the best fertilizer for rhododendrons?Liquid or water-soluble fertilizer is mixed with water and then poured into the soil. If you are concerned about cost, granular fertilizer is the best fertilizer for rhododendrons since it is the cheapest. Liquid fertilizer passes quickly through the soil and application must be repeated more frequently.Likewise, are coffee grounds good for rhododendrons? Lower Soil pH It’s always a good idea to add coffee grounds to compost, but mixing it directly into the soil can help balance alkaline soil or give a boost of acidity for plants that prefer a lower pH, like hydrangeas or rhododendrons. Thereof, when should I feed my rhododendron in pots? Sprinkle a small handful of pellets around the plants in early spring and repeat as the flowers fade. If the weather is dry, water thoroughly after application. Vitax Azalea, Rhododendron and Shrub fertiliser can be used on plants in pots and in the open ground.Is bone meal good for rhododendrons?It is very important that this be a fertilizer for rhododendrons. Other flower fertilizers use a bone meal base for their center number, which is a lime, and lime is lethal to these acid loving plants. Rhododendrons do require a little more work than other plants, but the beauty they produce is worth the time.