Can I plant blackberries in the same vicinity as raspberries? Can I also plant grapes and blueberries in the same vicinity as the other berries?
You can as long as they are all domesticated varieties and certified virus free. Do not plant wild varieties of any kind of berry near domesticated ones as the wild varieties may carry diseases.
Can you root a piece taken from the blueberry plant by just putting the end in water?
Yes, you can do this. You will have more success with putting the cutting in moist soil, but water will work more often than not.
How often should a very small blueberry plant be watered? We just planted it today.
I would water it daily for at least two weeks, to help it get established. After that, make sure it gets 2" of water a week.
When do the following blueberry plants bear fruit (i. e. early, mid summer, late) in northern IL: Arandrano, Bluecrop, Elliot and Northland. Thank you
Bluecrop and Northland will ripen before the Elliot. The first two should be ripe around late July or early September and Elliot should be ripe by mid August to September. As for the Arandrano variety, I am unfamiliar with that one and would not be able to tell you when it ripens.
Can I prune blueberries in the middle of winter when there is still a chance for snow?
Yes, snow is ok. Deep freezes are the bigger concern. If you are still expecting some deep freezes, wait a bit longer.
How do you prevent these bushes from growing taller and wider? Is it ok to cut back taller branches to a height of 6 or 8 feet?
Yes, that would be fine. It will not harm the plant. This article will help you as well: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm
I just bought two Jersey blueberry plants. Is it necessary to buy another type of blueberry plant to cross with these? Also, should they be planted away from other fruit, such as blackberries?
They don't need to be cross pollinated, but they produce better if they are cross pollinated.