Is there any better day of the month or sign of the moon when you can plant blackberries or cuttings?
Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/vegetables/vgen/planting-by-moon-phase-fact-or-fiction.htm
I live in Brooklyn, NY (zone 6). I planted blackberries in the spring. They grew great but the fruit came too late. I want to move them to a sunnier spot. I already cut it down because the branches bore fruit. It's going to be in the forties for the next week and mid thirties at night but not freezing. Can I transplant them now or should I wait for the spring?
You'll want to transplant your berries early in the spring. This article has more information: https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
My blackberry bushes are about 3 years old. Last year I cut them back in the late fall. I fertilized the bushes in the spring and then watered regularly the following spring/summer, but the bushes did not produce any fruit. Are blackberry bushes supposed to be cut back? (note that the previous year they did produce, when I cut them back, but I did not cut them back very far.)
Here is more information that should help with pruning your blackberries: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
Blackberries only produce fruit on the old canes. You selectively prune blackberries if they get to big or to bushy. Just prune some of the old canes back. It does not hurt them to cut them back but you will lose your next years harvest.
Can blackberries be grown in containers? They came up and then disappeared. I think bugs got them.
Yes, blackberries can be grown in containers. You can read more about berry container planting here: https://www.gardeningknowhow.com/edible/fruits/berries/berries-growing-container.htm
There could be a number of reasons that your seedling plants disappeared besides insects. They could have been eaten by rabbits/deer or the seedlings could have shriveled up and died (damping off disease possibly due to over-watering).
For more information on growing blackberries, please visit the following link:
https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
From the base of my blackberry vines grew a thick stalk 5 times the size of the other vines, more like a sunflower size. The stalk has similar leaves but much bigger than the leaves on the vine. There have been no flowers for fruit just a thick stalk. Do you know what this might be?
It sounds like you may have witches broom. This article will explain more about the condition:
https://www.gardeningknowhow.com/ornamental/trees/tgen/witches-broom-disease.htm
Will the new shoots bear fruit? I have some blackberry bushes that were damaged by the severe cold in winter. I had to cut all the canes to the ground since they did not grow leaves. There was significant new growth that should have bore fruit this year. Again, the canes from last year did not grow leaves this spring. I again had to cut all the canes to the ground. I have significant growth from the base and I also have shoots many feet from the main bush. Should I expect the new canes to bare fruit next year or is the bush permanently damaged? Should I start over with the runner shoots?
The new growth this year should produce berries next year. If your bush was permanently damaged you would not be seeing any growth at all.
For more information on blackberry bushes, please visit the following links:
https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
Plants only produce small size fruit. How do I get my Blackberry plants to produce large fruit?
I would review this article on the care of blackberries, as following these guidelines will help produce better berries:
https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
Furthermore, this article (PDF) from Cornell University discusses pruning techniques that may encourage larger berries:
https://bit.ly/1LDlF7G