Q.Should I cover my flowers with a plastic tarp when it rains?
I have a raised wooden homemade flower box over concrete. It has a plastic tarp at the bottom beneath the soil, but I drilled holes so there is drainage off the sides.
Would covering my plants with a plastic tarp before a storm prevent them from getting waterlogged and or broken/ripped up in the wind?
I have marigolds, zinnias, and petunias which are all pretty top heavy/delicate. I just transplanted them 3 days ago.
Do I also have to cover my potted plants?

Sure, during heavy rain periods or storms you can cover your plants. Be sure to uncover as soon as the rain stops!