With that many plants in a wall planter you were going to need more rather than less watering, especially if they are in full sun. Our local town water their large hanging baskets every day to ensure that they don't dry out. If you planted them in new compost there should be plenty of nutrients to help them grow.

If you feed with a high nitrogen fertiliser, then you will get more leaf than flower. As MG says, there is some feed already in new compost but as you will be watering regularly then the feed with be quickly washed away. If you wanted, then you can still sprinkle slow release granules on top of the baskets. For best flowers you need to feed with a high potash fertiliser such as Tomorite or Maxicrop Tomato fertiliser when the plants come into flower.

And the only stupid question is the one you did not ask when you could have done.

Thanks to you all.
Moon grower - I understand my watering regime will have to be a bit more consistent, but Geraniums are a bit more tolerant than many plants. The old ways were keep them dry and the poor things frantically tried to flower and set seed before they died, hence more flowers. I don't intend to go that far and they are near the back door so I remember to water.

Thanks Jimmy, I have some Tomorite somewhere lurking in the back of the shed so will dig it out and actually use it. And there is some slow release pellets in the basket, so I will cover all bases.

You are right of course Owdboggy, how many times can you say "why didn't I ask" before it sinks in that there is always someone who will know.

Honeysuckle the fact that you say 'flower and set seed before they died' indicates that they were fairly short lived, if you want them to keep flowering through the season then a good watering regimen is going to be necessary. A good soak a couple of times a week will be better than a daily dribble.