Answer: In some instances vines grow very lushly but fail to flower because they have been supplied with too much nitrogen. Generally too they are trained onto a trellis or into an area where they may sprawl unhampered rather than pruned since pruning can weaken the plants -- it is amazing how large a single vine can grow! Although the trellis is in full sun I suppose it is possible that they are shading each other somewhat especially if they are crowded together so this may also account for poor flowering. At this point I doubt there is much you can do to encourage blooming except wait. In preparation for next year, however, you might run some basic soil tests so you will know how much (if any) fertilizer your plants will need.
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