Why don’t roses open fully

The arrival of wet weather often brings with it a wide range of plant diseases and disorders – none more disfiguring than rose balling in which the flowers fail to open. Although this can occur pretty much any time when roses are in bloom, it is regularly seen in autumn, at the end of the flowering season.

It is caused when the petals of the flower become fused together by moisture that settles between them. Without air, the damp cell surface of the petals starts to break down slightly, gluing them to their neighbours to prevent them from expanding and the flower from opening. The effect is compounded during alternating sunny spells when the tissues dry and effectively ‘weld’ the petals together.

The phenomenon is most common is heavily double flowered rose blooms – those with many petals. It is also problematic in varieties that have well-defined cup shaping to the individual petals. In addition it is more common in very wet seasons, where periods of drenching rain are interspersed with sunshine. In many cases, especially in autumn, a secondary infection of grey mould (botrytis) can occur on the blooms, but this is generally not the initial cause of the balling.

Flower balling can occur in other heavily petalled double flowers, most notably peonies and sometimes in camellias.

How can I prevent rose flower balling

Heavily petalled flower forms are best planted in open, airy and full-sun locations where their blooms stand a better chance of drying out between rain showers. Opening up rose bushes by pruning to outward facing buds, before growth starts in spring will help by allowing air to circulate through the centre of the plant. This is often referred to as pruning to create an ‘open, wine-goblet’ shape.

During the flowering season, regular dead-heading of the faded blooms will help maintain good air circulation, too. In addition, removing any affected flowers will stop the secondary grey mould infection which can compound the problem. Don’t over feed plants which high-nitrogen fertilisers as this will tend to promote very soft tissue growth that is more vulnerable. High-potash fertilisers will help make petals more robust as well as encouraging plants to be more floriferous.

Some varieties of roses and other plants are more prone to flower balling than others. Where the problem is very persistent it may be worth replacing with a less-vulnerable variety. Remember that this condition is exacerbated by high rainfall, so it tends to be much more prevalent in the western side of the UK and Ireland, as well as other wet climate areas.

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