My hydrangea has not yet bloomed. It is about 3 feet tall. How can I know what color it will be, and can I make it pink before it blooms?
You can hedge your bets on making it bloom pink before it blooms. This article will explain how to treat the soil to help with that:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/change-hydrangea-color.htm
Please tell me what to do about brown spots on the leaves of my hydrangea plants.
This may help:
https://www.gardeningknowhow.com/plant-problems/environmental/what-causes-brown-edges-on-leaves-of-plant.htm
and this:
http://msue.anr.msu.edu/news/bacterial_leaf_spot_on_hydrangea
Is cutting all flowers from the shrub considered pruning? A 3-year-old shrub profusely bloomed until this year. I cut all the blooms last fall and this year it did not bloom at all. The plant is humongous this year, healthier than ever. What happened?
You need to leave the flower heads until the following spring. Then cut them down to a couple of buds.
My hydrangea plant does not bloom at all.
This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm
Should I cover the Hydrangea in the snow or cut the plant down? My plants are at least 2 to 3 feet high.
This article will help you:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-winter-care-how-to-protect-hydrangeas-from-winter-cold-and-wind.htm
How do you prune, for example, a hydrangea? Also, what is the best way to put string around a plant that has gone astray - or bush for that matter?
Different plants have different pruning requirements, so we would need to know which plants you wanted to prune to give advise on them. Since you asked about hydrangea, this article can help with pruning that:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/prune-hydrangea-bushes-hydrangea-pruning-instructions.htm
If a plant has gotten too big for an area, it would be better to prune (or divide in the case of some perennials) rather than to simply tie it back. The plant will continue to grow, regardless of which you do. It is better to keep the plant manageable rather than try to tie up all of its growth.
How do we care for our hydrangea plants for the winter? Is there a need to prune them back and cover them with the styrofoam cones?
Try waiting until spring to prune it. Wait until you see what survived the winter and cut off the stems that did not. These articles will help:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/prune-hydrangea-bushes-hydrangea-pruning-instructions.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-winter-care-how-to-protect-hydrangeas-from-winter-cold-and-wind.htm