Anything that grows back from the roots such as flowers, hostas, ferns, or grasses can be cut down to the ground
Most plants and trees benefit from pruning. It promotes branching, leaf formation, and increased blooms. A regular pruning regimen also allows you to check for diseased or decayed material in the plant and get it removed before it causes a problem.
Most evergreens will show you how far you can prune them back because the needles or leaves are no longer present on the interior of the branches. A light trim leaving a couple of inches of the needles or branches will keep them in check and looking good. You can cut them back to the bare branches if you need a size reduction, just know that it may take a season or two for them to flush out new greenery.
Shrubs & Deciduous
Most deciduous and flowering shrubs benefit from a light pruning each year. Feel confident to remove 1/3-1/2 of the plant. This will promote branching and more blooms the next season. This practice will also help keep shrubs at the proper size.
Some larger shrubs (such as crape myrtles, butterfly bushes, and roses) that grow from the base of the plant need to be pruned back to 1′-2′, tall depending on size.
A few varieties of Hydrangea and some other flowering shrubs only bloom on “old” wood. This means you need to leave at least 1/2 of the branch length that is covered in leaves in order to get any blooms the next year. The “new” wood on the current year’s branches will not produce flowers. You may need to prune them more severely every 3-5 years to keep them to the proper size, just know they will not produce flowers the next season.
It is important to always use sharp pruners or hedge trimmers. Using dull blades can crush or shatter branches which can kill the branch and/or invite fungus and disease into the plant.
If you have a worry of disease or fungus on a particular plant, be sure to clean your pruners or hedge trimmers with a 10% bleach solution before continuing, to prevent spreading to other plants.
Light pruning and deadheading can be done at any time, but heavier pruning or “rejuvenation” pruning is best done during dormancy in the cold months of the year.