The inflorescences of Mentha longifolia consist of long, narrow, cylindrical spikes of small, stalkless, white to lilac or mauve flowers growing at stem-tips. A spike is about 100 mm long and 12 mm in diameter. The flowers are whorled at closely spaced nodes.
Each flower has a four-lobed corolla and is about 4 mm long, about 5 mm in diameter.
Flowering happens from late spring to after midautumn (Vlok and Schutte-Vlok, 2015; Manning, 2009; Bond and Goldblatt, 1984; iNaturalist).