Assuming the plant is adequately watered it's just a natural process. Hardy geraniums do not flower all summer long like pelargoniums.
This variety flowers early then sets seed but you can get a second flush if you trim the entire plant back to about 3" high once all the flowers have finished. Give it a feed and it will grow fresh foliage and, probably but not definitely, flower again late in summer. It is best planted in a border where it can mingle. Not a good subject for a display pot.
Vendée - 20kms from Atlantic coast.
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This variety flowers early then sets seed but you can get a second flush if you trim the entire plant back to about 3" high once all the flowers have finished. Give it a feed and it will grow fresh foliage and, probably but not definitely, flower again late in summer. It is best planted in a border where it can mingle. Not a good subject for a display pot.