Geraniums perform beautifully in part-sun for me. I'd say they need at least 5 hours, though, although if it is strong sun 4 hours would be fine too.

If they are Martha Washington geraniums, they don't perforum well in hot weather. They like the cooler Spring weather better. The other geraniums do well like mxk said. Also, remember to fertilize with one that has the middle number highest. That helps the plant produce more flowers. I use a 10-15-10 about every 2 wks on my flowering plants.

Kat

I have an ivy geranium in a wire planter hanging on my patio that gets full sun from about 1 in the pm till the sun goes down, mine is doing very well, but I have to water it everyday and sometimes 2 x's a day, dur to the heat and the planter.