Definition: "useful around the garden"

This is a charade - where separate parts are joined together to form the answer word.

Break this into two parts: 'Son' gives you the first letter, and 'in better shape' describes someone who does the trimming. Put them together.

Answer: STRIMMER | This is a charade of S (son) + TRIMMER (in better shape, as someone who trims is trimmer than before).