I live in Franktown, Colorado. The blossoms just started a week ago. We had a
I'm sorry, but the question is not complete. I am assuming that you are worried about the blossoms being damaged by the sudden onset of cold, wintery weather in your area. This really depends on the plants in question and how low the temps get. Unfortunately, some plants cannot handle ANY cold weather and will become easily damaged by cold. Covering them when cold snaps are expected helps.
I live in Illinois and the weather got warm and all my plants are up. Now it's got cold and suppose to stay cold for awhile. What do I do for my flowers and plants?
Most of the hardy spring blooming plants, like bulbs, should be fine. However, the others may need protection IF frost or freeze is expected. These articles will help should this be the case: https://www.gardeningknowhow.com/plant-problems/environmental/frost-how-to-protect-your-plants.htm
We are expecting near or freezing temps the next 3 nights (28 degrees to 34 degrees). I have covered most of my perennials that are a least a month ahead of schedule because of our mild winter and early spring temps. How long can I leave them covered, or do I need to uncover them daily and then re-cover? I have lots of plants and not a lot of time. I guess my question would be, can I safely leave them covered with paper sheets and buckets for 3 days?
No, you cannot leave them covered. They must be uncovered each day, or they may suffer for the lack of light.
Can I cover plants at night with sheet or plastic bag to protect flowers?
Yes, a sheet is fine. This article will help: https://www.gardeningknowhow.com/plant-problems/environmental/protect-plants-in-freeze.htm
Will putting a large tarp over the plants with the sides open about 3 feet be sufficient to protect plants from freezing?
Yes, this should be fine as long as you remove it in the morning. This article will help with covering the plants: https://www.gardeningknowhow.com/plant-problems/environmental/protect-plants-in-freeze.htm
Do all vegetable plants need to be covered when threatened with frost?
Most do but those that are cold hardy like root crops (turnips, carrots, beets, etc.), some greens, and cole crops (broccoli, kale, cauliflower) should be fine with light frost.
What is the best way to ensure that late planted perennials will become established and survive the winter? And same question for late planted shrubs and trees.
This article should help: https://www.gardeningknowhow.com/plant-problems/environmental/protecting-plants-winter.htm