The new spines are initially reddish to magenta and fades to a yellow or light pink color when they mature.
Echinocereus rigidissimus flowers in flushes throughout the spring season, with multiple buds borne atop the plant from younger areoles.
A 2018 measurement of one plant in the Santa Catalina mountains showed a height of 48 centimeters, a record.
Flowering occurs from late April to early June depending on the elevation and spring heat.
The specific epithet rigidissimus is the comparative of the Latin word rigidus, means 'stiff' and refers to the thorns of the species.
Echinocereus rigidissimus requires full sun to part shade during its active growing season from spring through to early autumn, as well as adequate air circulation to reduce the chance of rotting.
In winter abstain from watering Echinocereus rigidissimus and keep the soil mixture dry, as it helps encourage flowering in the spring season.