|Had the plants - NOT grown from seed - for about 10 years.
So far, no blooms.
What am I doing wrong and what should I be doing,
or they hopeless after all this time?
|Grafted wisteria have a better chance of becoming floriferus; seeded wisterias are nearly always "mules" so by planting a grafted cultivar, you should eventually see flowers. It can take up to 6 years for a wisteria to establish itself in a garden. After the 7th year it usually blooms. There are two other things that might stop flower production - pruning at the wrong time (or in the wrong way) and lack of sunshine. If your plant is in full sun, it should bloom; if not, it may never. You didn't mention your pruning practices. An unpruned wisteria will product rampant growth but won't necessarily bloom; a pruned wisteria - if properly pruned - will respond by producing flowering shoots.
As for pruning, try a major cut back this winter, cutting back almost all of the previous year's growth to leave just three or four buds per stem, one of which would be plumper and become a flower three months later. This summer (July) you can trim back the new runners to 5-6". They will branch and lengthen - you can safely prune them back every few weeks all summer long. This will promote lots of shoots, many of which should set flower buds.
Some growers feel it also craves phosphorus, the ?flowering nutrient?, so folks with no flowers might want to scratch a couple cups of bone meal into the soil now and then, and add some rock phosphate in the Fall.
Hope this helps you!