Thank you for that information. So being 'root bound' means they have no more space to grow because not enough soil, or not enough nutritious soil? Yes, there are 2 plants together, but we also have another old geranium in a different location that are not blooming as well. There are 3 together in that bunch. This does make sense, but how do I dig them up and remove/replace, won't I destroy the old roots? thanks!

Dig them up with a garden fork if you have one. If not a shovel will do. Dig further out than the plant and not directly under it. The feeder roots will have spread out to where the ends of the tops are. It won't matter if a few of the roots get broken off. You are trimming back the tops too and so the plant won't need all it's roots. Water it but don't over water. Geraniums don't like wet feet. I like to pour water in my hole I've dig for planting and let it soak into the ground. That way the roots hit moist soil as soon as they are planted.

Do this on a cloudy day so the plant does not have to cope with heat and being transplanted. If you do do it on a sunny day then shade it somehow. I like to put an upside down pot over any transplants and leave it on for a couple of days. This not only shades the plant until it can set down roots it keeps the moisture from the water you've poured in the hole around the roots. You'll see when You take it off that there is a ring of moist soil around the plant.

Good luck

Thank you! Just so I understand...what you're saying is not to dig the entire plants out but rather dig out, fill with good soil, water - on both side so the roots have more space to grow?

Geraniums tend to wear out after so many years on their old wood, and they get unattractive and non-blooming. I always prune my plants hard in the springtime and then stick the best of the clippings in the ground, making sure a couple of “joints” are buried in the soil. New, revitalized plants will grow quickly from these, provided you’re careful not to overdo the watering.

Easiest thing to do is to just prune them back severely. Make cuts into the old wood and remove most of the tops. You'd be surprised how quickly they will grow back and re-bloom. If you're still hesitant, then test it and cut back just one of the plants to see what happens. I prune mine back several times during the year to keep the plants compact and blooming.