Do the leaves have rusty brown bumps on them? Hollyhock rust is a very common fungal infection and shows up as leaves turning brown. Check the backside of the leaves for bumps of rust. The cure is to keep the foliage dry and the plants well fed and watered to resist this fungus. It is also possible they have a viral infection - look for yellow streaking in the leaves. If the rest of the plants nearby are healthy I would remove the hollyhocks so as not to contaminate the others and give them a new location next spring with fresh plants. Sometimes hollyhocks do great with very little attention - and sometimes hollyhocks become disease magnets. It is such a lovely old fashioned flower but it comes with a challenge. Keep growing, Marianne Binetti