Although Brachystelma modestum occurs in a high-rainfall region, where rain may fall regularly in the summer months, the thin sandy substrate upon rock in which it grows does not hold moisture and dries out rapidly. Tubers remain damp for only brief periods. It is difficult to replicate this environment in cultivation. For this reason, and like certain other Brachystelma species with tubers, they require high maintenance and are prone to attacks by fungi and mealy bug.

Brachystelma modestum is best grown in shallow terracotta pots or asbestos trays in morning-only sunlight or light shade with the tuber partly exposed. The best germination medium is a fairly heavy soil since this retains some moisture for longer periods than sandy soil, in the shallow containers. Pots should be watered occasionally in winter months to prevent the tubers from shriveling. Seeds generally germinate within two weeks after sowing and watering, but this process is variable and can take up to almost five weeks. Plants should not be over-watered.