The Q&A Archives: Few Blooms on Rhododendrons

Question: I have several varieties of rhododendrons, of varying ages. The oldest (25 years) has a great many flower buds, but three others, as well as a mountain laurel, hardly have any this year. What can I do to get more blooms next season?

Answer: Are these all plants which have bloomed well in the past, but are failing to flower just this year? Failure to set flower buds sometimes results when a plant is producing vigorous foliage growth, possibly due to overfertilization, especially with a high nitrogen fertilizer. Do the plants look vigorous and healthy? Have you fertilized them recently? Note that many lawn fertilizers are high in nitrogen, so if there's any chance some lawn fertilizer was applied near the bushes, that could be a factor.

Other factors: failure to deadhead soon after flowering can inhibit flower bud formation for the following year; cold, wet weather in the previous June/July can sometimes cause a flush of foliage growth--usually, this is a time when the plant is forming flower buds. And since the plant flowers on one-year-old wood, any pruning done last summer or fall could have removed flower buds. If the plants are in very dense shade, that could also be a factor.

If you think the lack of flowering could be due to overfertilization, you can try root pruning, by cutting around the perimeter of the bush with a spade. This sometimes checks excessive foliage growth, and stimulates the production of flower buds.

I hope this helps!

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