Rhombophyllum rhomboideum can be propagated by seeds or cuttings (splitting) in a well-drained media. Even though it may survive excessive watering, the plant requires moderate watering while positioned in a sunny spot.

Seed sowing is ideally done in spring, while plants are actively growing. Use seedling trays and growth medium containing 1 part river sand, 1 part sifted red soil and 1 part sifted compost. With the drainage of germination trays supported by coarse particles such as bark, crushed stones etc. at the base, fill trays with growth medium and moisten it. Scatter seeds evenly on the growth medium surface and then add a thin layer of the germination mix to anchor the seeds and prevent them from moving over. The layer should be minimal to allow sunlight to reach the seeds, since it is needed for germinating the diamond-leaved rhombophyllum. Place the trays inside the greenhouse receiving indirect sunlight, with a temperature ranging between 21–26°C. Then water seed trays on a daily basis using a misting sprayer, until they germinate. Where germination is practiced at home, trays can be gently watered and then sealed with plastic to retain moisture until seeds germinate, with regular misting when needed. Germination can be achieved in the first 2–4 weeks after sowing, provided that the conditions are constantly kept favourable. When seedlings are established, gradually expose them to more light and airflow before transplanting, until they can withstand direct sunlight. Hardened off seedlings can be transplanted into suitable pots using potting mix suitable for succulent plants.

For vegetative propagation, R. rhomboideum is best propagated by splitting. Propagation by splitting involves separating naturally formed offshoots from the parent plant (division of offsets). Splitting is best done early in the morning, while the plant hormones are active and the temperature is cool. When the plant has formed a dense clump, carefully remove the plant from its pot or loosen the surrounding soil. Identify individual offshoots that have their own roots or are sufficiently developed, with at least have two sets of leaves. Gently pull the offshoot away from the parent plant; if necessary, use a clean, sharp knife or secateurs to separate offshoots from the mother plant. Allow the separated pieces to dry for few hours so that any wounds can callus, reducing the risk of rot. Offshoots with roots will gain a survival advantage, but the ones without roots also stand a chance to survive. Use a well-draining succulent mix with a high content of river sand to pot up offshoots in small, shallow pots or trays if there are many. After planting, do not water immediately, spare few more hours to allow any damaged parts to heal. Place the containers in a bright, well-lit area with indirect sunlight initially; avoid harsh direct sun until the plants are established. Once rooted, the plants can tolerate full sun to partial sun, similar to their natural habitat. Maintain warm, dry conditions, as the species is adapted to semi-arid environments.

The diamond-leaved rhombophyllum looks great when cultivated as a pot plant, placed in a sunny spot receiving indirect sunlight. Grow it in a well-draining succulent potting mix, such as 1 part river sand, 1 part red soil and 1 part compost or any organic medium. Ensure that the soil pH is neutral to slightly acidic (6.0–7.0). This plant does well with minimal watering, though it may survive regular watering. This species is suitable for dry, rocky gardens designed for low maintenance. Grow the diamond-leaved rhombophyllum in dry climates, in full sun to partial shade. The soil should be well-draining and with moderate to low water-holding capacity. Water the plant well during spring and summer, and sparingly in autumn and winter (dormant season) – ideally once every two weeks to a month.

Rhombophyllum rhomboideum may suffer from root rot caused by overwatering and poor drainage – which should be avoided at all times. Additionally, given the smooth thick leaves of this species, the plants may be attacked by white scale, which is a common sap-sucking pest on succulents. Spray the plants with insecticidal soap or neem oil solution, covering all surfaces. Repeat the application every 7 – 10 days and wash the scale off with high pressure water. To prevent the plant from hosting pests, often remove dead or damaged parts from the plant.