THE PROBLEM SOLVER
Stefan Buczacki
Professor Buczacki is a horticultural expert, writer and former chair of Gardeners' Question Time
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Stefan says: You have a plant, six years old, of the beautiful yellow-and-orange-flowered rhododendron, ‘Horizon Monarch’. It grows and blooms well in your sandy soil, that you regularly enrich with ericaceous compost. However, this year, one side is looking sparse, slightly yellowed and it appears the new flower buds have died off. Small shoots have appeared either side of the dead bud.
I’ve looked carefully at your pictures and don’t think the yellowing is serious. When rhododendron foliage is stressed, the yellowing is much more pronounced and the veins tend to stand out as dark green. Most of the foliage on your plant looks healthy, so I do think it is genuinely a one-sided effect. I’ve also studied the pictures for any signs on the dead buds of a disease called bud blast that is spread by the rhododendron leafhopper insect, but I couldn’t see any.
My primary suspicion, therefore, is that there has been damage – most probably root damage – to one side of the plant. This has had the effect of limiting water uptake on the affected side and the flower buds have suffered. All I suggest you do is cut back the affected parts, ensure the plant is not allowed to dry out, give a liquid ericaceous plant food, then wait and see what happens.
But I should say a word about diseases caused by predominantly soil-inhabiting pathogens called Phytophthora. These have received considerable publicity relating to rhododendrons in recent years, because rhododendrons are the host plants for several different kinds of Phytophthora which can spread and cause problems on other types of shrub and forest trees. These diseases are extremely serious and must be notified to the Department for Environment, Food and Rural Affairs, but I think it’s most unlikely that a well-established, isolated garden plant such as yours is affected. If you are in any doubt or are still concerned, do ask an experienced local expert to look at the plant.
FOUR MORE RHODODENDRON PROBLEMS…
Like many shrubs, rhodos can be prone to powdery mildew in humid warmth. Prune lightly to open up.
A fungal problem mostly on azaleas, causing pea to plum-sized white galls. Pick off any you see forming.
Caused by various fungi; purple or brown spots appear on leaves. In severe cases, leaves can drop off.
Rhodos are very susceptible to honey fungus. You may see the telltale mushrooms forming in autumn.
What will happen to the runner beans I left in the ground last year?
Stefan says: Because you were away, you left your runner beans in the ground last autumn and have now seen some signs of life. Wh
