'soft-stemmed' originates from Modern English, specifically the compound 'soft' + 'stemmed', where 'soft' meant 'not hard' and 'stemmed' is the past-participial/adjectival form of 'stem' meaning 'the main stalk of a plant'.

'soft' ultimately comes from Old English 'sōfte' (from Proto-Germanic *samftaz) and 'stem' from Old English 'stǣm'/'stemn' (from Proto-Germanic *stammaz); the hyphenated compound 'soft-stemmed' is a relatively recent Modern English coinage combining these elements.

Initially, the elements separately meant 'not hard' and 'plant stalk'; together they evolved into the descriptive compound 'soft-stemmed' meaning 'having non-woody stems'.