Geissorhiza mathewsii is best propagated from seed sown at the onset of cooler night temperatures and the arrival of autumn rains in the Western Cape, usually from early autumn. Sow seeds in deep seed trays or beds designated for bulb cultivation in full sun. Use a well-draining soil medium of river sand or Malmesbury sand, and sieve the soil if it contains too many fine clay particles that reduce drainage. Seeds can be sown in rows or evenly scattered, then covered with a thin layer of soil due to their small size. Keep the soil moist at all times, as it must never dry out. Avoid sowing too densely, as overcrowding slows growth and increases the risk of fungal disease. Once germinated, keep seedlings moist and apply an organic foliar spray regularly. Watering should continue until the leaves begin to yellow near the end of spring, at which point watering should stop to allow the little corms to enter dormancy. Leave the seedlings undisturbed for another full season before lifting and dividing them. Store corms in breathable brown paper bags in a cool, dry place over summer and replant them when the growing season begins again. Some seedlings may flower in their second year of growth.

Mature plants grow best in full sun under potted culture. Deep plastic or clay pots are ideal, as they retain moisture and buffer temperature fluctuations. Plant corms in autumn, placing them at a depth two to three times their height in a well-draining medium such as river sand or Malmesbury sand that has been sieved to remove excess clay. More expensive mediums like akadama and pumice are also very useful but can be expensive and require more regular watering. Before planting, mix an organic fertilizer containing phosphorus into the root zone and space the corms evenly so they do not compete for nutrients. After planting, soak the soil thoroughly until water drains from the bottom of the pot, then withhold further watering until leaves appear. Once the first leaves emerge, water regularly to prevent the soil from drying out, as drying will induce premature dormancy. Plants benefit from organic foliar sprays throughout the growing season. Snails and slugs may feed on the leaves and flowers during the wet winter months, but this can be managed using beer traps, organic snail pellets, or manual removal at night.

Flowering typically occurs in late winter and spring, from late August to early October. During this period, hand-pollinate flowers to increase seed stock and maintain a backup to the mother plants. If cultivating more than one winecup species, use a pollinator exclusion structure for outdoor setups to prevent cross-pollination and hybridisation. If seed production is not desired, remove flower spikes soon after blooming to allow the corms to build reserves for the following season. As temperatures rise, aphids and thrips may infest leaves and flower spikes, causing deformation or flower loss if untreated. Remove them manually if numbers are low, or use an organic pyrethroid spray for severe infestations. Products containing garlic are particularly useful, as they also deter future infestations.

Once flowering ends and the leaves begin to yellow, stop watering to allow dormancy. After the plants have fully died back, lift the corms and inspect them for pests and disease. Mealybugs are often found on dormant corms and can be removed by hand before dusting the corms with flowers of sulphur or diatomaceous earth. During the growing period, premature leaf yellowing and flower abortion may indicate a Pythium or Fusarium infection affecting the entire pot. In such cases, flush the soil with a solution containing the active ingredient dimethyl-didecyl-ammonium chloride at the recommended dosage. This treatment is safe for plants and, with repeated applications, effectively eliminates pathogens even in poorly draining soils.