Pinching out the growing tips is a process where once the clematis begins growing you pinch out the main stems to allow basal side shoots to develop. Following are picture which illustrate this.

Here is a clematis plant emerging from the ground.
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Here is the clematis with me pinching out a growing tip thereby leaving two side shoots to develop into main branches.
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Here is the plant with two stems pinched out.
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Once the main stems are pinched out, I will allow the side stems to grow and develop two or three sets of leaves and then pinch out the main stem again. Each time you do this, it results in the plant developing two more stems. This also tends to encourage more stem development from the soil line.

Awk!!! I didn't know you were supposed to do that. Can you take the part you pinch off and root it? I have a 3-4 year old vine that is blooming, but it doesn't get the all over bloom I have seen on other plants. Maybe I need to start pinching. Can you do this on an existing and blooming vine?

Thanks,

Cathie

Scarlett, you don't have to pinch out the growing tips. If you do however you will have more branches and leaves on your plant which in turn means more photosynthetic surfaces. The more photosynthesis the more food the plant can synthesize which ultimately will mean more flowers! Also pinching back like this is best done on young plants because it will encourage root growth over top growth which is good for clematis as they are becoming established in their new homes.

I personally don't attempt to root any of the branches I pinch off because they are softwood and aren't very likely to root anyway.

I would hold off if your plant is currently blooming. After blooming, what I would do is cut the plant back by half, fertilize it and keep it watered well this summer, and depending on your growing zone, you might be rewarded by a second flush of blooms.

I planted a new clematis (Jackmanni) but after I have pinched it off...about 2 feet from the ground....it hasn't done a thing!! Does it take a while? should I have waited to pinch it off the second year? It was really growing and as it got to the line I have strung up, I thought that would be a good "pinching" spot. Did I do something wrong?
thanks!

Did your plant already have side shoots coming out from the leaf node above where you pruned it or were they still dormant? How long ago did you pinch the top out? Answers to these questions will help with any responses you might get.

Generally speaking if the nodes were dormant, they don't immediately get called into play. It takes time for a plant to respond to pinching out the growing tips. Pinching off growing tips or even hacking back a clematis should not stop it from growing provided it has been feed and kept watered. I think you need to give the plant some time to respond.