The blackberries look good until they turn black, and then they develop dry brown seedy areas. We had an unusually wet spring, and now temperatures over 100 for a week. Central Washington state.
This is what is known as White Drupelet Disorder. It can be caused by several things, from sunscald, to high temperatures and wind, to a few types of insects. This article will offer more information, and ways to prevent this in the future:
https://www.gardeningknowhow.com/edible/fruits/raspberry/white-drupelet-syndrome.htm
I've repotted into bigger tub still no luck.
It looks good. Many factors can be considered regarding your blackberry plant. If the plant is still too young, it may just need more time. If the plant is stored in that container outdoors, the newly formed flower buds may be injured from cold weather. Or, if you leave the plant indoors, it may not receive enough dormancy or "chill hours" to set buds. Also, if you have pruned the plant annually, it may have been at the wrong time.
For more information on blackberries, please visit this link: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberries-not-fruiting.htm
The article by Mary ellen ellis was unclear. I got starts for a thornless blackberry from a friend and was told that only 2nd year canes would bear fruit! SO I have pruned the last two seasons all old ( fruit bearing)canes by the end of the fall! I have not seen any production of the new canes in the fall? This years growth seems less vigourous then the previous year when new canes grew up to the gutters! So does only one type of cane grow each year,?, I have shared canes/starts with several friends last year but have not gotten any feedback. I need to go look at new growth from starts I shared last year and this year. I purchased some (3)Heritage Raspberries last year and then reordered 3 more when only one plant survived over the winter. So both types of canes produce fruit but one may grow bigge and not fruit until the 2nd year, but the 2nd will have more fruit over 2 seasons? ,
They will fruit every two years, and benefit from pruning out canes that have already fruited. The old cane that has fruited will not bear again. These two articles are a little more clear (although one has quite a bit of information that you won't need.)
https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
I just planted a blackberry bush this summer. It hasn't produced any fruit yet and is still pretty small. What do I need to do to get it through the winter?
Unfortunately, summer is quite late in the year to plant blackberries. It may be that it was stunted from late planting. As long as you know that you have a cultivar that will survive your zone, then there isn't much that you have to do for preparation, except for pruning. This will be determined by which kind of fruiting habit your blackberry exhibits.
As far as fruiting- This could be for a couple of reasons. Most, likely, due to late planting. Next would be knowing whether it fruits on this year's growth or next year's growth, but most fruit on older, 2nd year canes.
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-bushes-in-winter.htm
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm