hi,gerry,i planted a blackhamburg 25 yrs ago in a unheated green house.i traned it as single rod.the rod developed to 25 ft and produced about 30 bunches of lovely grapes.but for the last three years it has produced no flowers or fruit but plenty of lush foliage, I did all the necessary nipping out each fruiting stem is based 1 ft apart. The rod is planted in a 3ft square. Can I get it to fruit or is the vine exhausted? Its a very mature vine and I would be reluctant to loose it. Hoping you can help. Blackburg,
It seems strange if you did not change your normal practice that the vine would perform any differently. If yo pruned hard, this might happen, or fed too generously.
Try some potash at 30gm per square metre in spring, each year for 3 years, and revert to your normal practice, if it was changed.