Lack of rain can be a problem, especially during the main growing season. Clay not so much of a problem as that is what I garden in. Continued application of an organic mulch that will break down and add tilth to the soil will help in the long run. The past two years we have had drought conditions during the heat of the summer and for me the type IIIs handle those conditions better than the more delicate type IIs. I do have to water though. If you purchased the plants bareroot, it might be better to pot them up for a season and plant them in the garden during the fall or winter, depending on when you tend to have the most rain. This will allow the plants to get established during more hospitable conditions and not have to try and get established during the hotter and drier months.

You can still prune them

No you don't have to prune your pruning group 2's right now..Enjoy those blooms and after it is over blooming then you can prune to induce more vines to emerge from the soil..hopefully..you have already hard pruned your pruning group 3's as they will bloom later on in the season on the new vines they produce...Jeanne

It is never too late to prune a clematis :-) Yes, it could delay or alter bloom time but in a mild climate with a long growing season, it is not going to have much of an impact. When I worked for a wholesale grower of clems, the vines used to get cut back routinely every month or so just to keep the pots/vines from becoming tangled up with each other. All this did was to encourage more basal stem growth, generally considered a good thing :-) Never affected the flowering to any significance.