Don’t prune hydrangea stems; The new blooms grow on the woody stems.
Don’t prune roses too low; Since many roses are grafted onto the roots of another kind of rose, if you prune too low to the ground, what comes up will not be the hybrid your expected but another type altogether.
Don’t prune woody herbs too low or too early (or maybe at all); Certain herbs – lavender, thyme, sage and rosemary – are woody plants. Just like trees, if you cut them down, they die. Pruning one too low is likely to kill the plant or injure it severely.