There are several common causes linked to Rhododendrons and Azaleas not flowering – here are the most common and what you can do to help flowering next season.
Drought or overwatering: These environment factors put so much stress on the plant that they do what all plants do in this situation – shed the flower buds to give the main plant a chance of survival.
Flower buds start forming in late summer – dry conditions at this time can cause flower buds to fail, or only partially form, drying up and dropping in spring.
Both Rhododendrons and Azaleas are shallow rooted and need to be in acidic soil with a pH of between pH 5.0 and 6.0, which is well-drained. Apply an 8cm-deep loose mulch of chipped conifer bark or other acidic organic matter from July to minimise the roots drying out.
Overwatering and planting too deep in a heavy soil will lead to root rot which kills the plant – often a first sign is dropping or discoloration of flower buds.
Frost damage: Avoid frost pockets and sites exposed to early morning sun in winter and spring, which will ruin delicate flower buds. Avoid open, east-facing sites.
Poor light: In deep shade, a plant will produce leaves and elongated growth at the expense of flower buds in an attempt to reach better light. Move the plant to a position in dappled shade.
Rhododendron leafhopper and bud blast: Leafhoppers are sap-sucking insects are active from late spring to autumn. Bud blast, a fungal infection associated with the insects, spoils developing buds.
The nymphs (young) are creamy white wingless insects that live on the underside of the leaves. Adults are 8-9mm long and have pale yellow heads and a bluish green thorax. In sunny weather, they can be seen on top of leaves, ‘hopping’ off when disturbed.
The problem is that females cut into next year’s flower buds in late summer/autumn. These are thought to provide entry points for the fungal disease bud blast (Seifertia azalea). Infected buds turn brown and die.
Infected flower buds should be picked off and disposed of (never composted) to reduce the amount of fungal spores in the area.
Wrong pruning: Flower buds form from late summer – any pruning needs to be carried out immediately after flowering in spring/early summer. If you cut back your plant in autumn or winter, you will cut off the next season’s flowers.
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Mandy Watson is a freelance journalist who runs www.mandycanudigit.com.
A plantaholic with roots firmly planted in working-class NE England, she aims to make gardening more accessible to the often excluded – the less able, the hard-up or beginners.
Advocate of gardening for better mental health.