This is a problem that could be asked at almost any time in summer but as these flowers were affected last week it seems an appropriate time to pose the question; what is this and what causes it? The plant is obviously a rose and the problem is usually called ‘balling’. Roses are the most affected flowers but it can also occur on peonies (rarely on other flowers). The outer petals of the flowers stick together and prevent the flower from opening. Sometimes the flowers go grey and mouldy but sometimes the inner petals continue to develop and the buds are pushed off the plants. It is most common in wet weather either in summer or in autumn when heavy dews form on the flowers and the sun dries the outer petals. Some cultivars are more prone than others and the usual advice is that thin-petalled flowers are more prone than flowers with thick petals. In peonies it tends to be the doubles that are most affected. But this rose is the otherwise reliable ‘Absolutely Fabulous’. You may notice that a later-developing bud has opened its flower normally and this particular spate of balling was associated with a spell of several days of wet weather.
There is not a lot you can do about this problem and if a rose is particularly prone it may be best to replace it. Otherwise praying for some sunshine is the best course of action and always worth doing anyway.