Gardeners use the word to distinguish plants from a shrub that have lower height , typically less than 10 -- 20 cm tall , or that are only weakly woody and\/or persist only for a few years . It is distinguished from a shrub by its ground-hugging stems and lower height , with overwintering perennial woody growth typically less than 10 -- 20 cm tall , or by being only weakly woody and\/or persisting only for a few years .