Watsonia marginata is a tough, low maintenance, easy plant in cultivation. It is shown to best effect when mass planted, but also looks good when planted amongst other plants in the rockery, or mixed border where even when not in flower, its leaves provide interesting colour and texture. It is also a suitable subject for traffic islands or roadside planting in the winter-rainfall areas. Watsonia marginata will grow in containers, although the dwarf forms make better pot subjects, but it has a very vigorous root system and requires a large pot and must be repotted every year if it is to flower well.

This watsonia requires a position in full sun, or one that gets sun for most of the day, and well-drained, compost enriched soil. It is tender to frost, hardy to a winter minimum of -1 ºC / 30 ºF (Zone 10) and in cold areas, requires a warm situation that is protected from the morning sun. In the summer rainfall regions, it must be planted in sandy well-drained soil or lifted every season, as the corms tend to rot if allowed to get wet during dormancy. Corms should be planted in autumn (March to April), whilst still dormant, at a depth of approximately twice their diameter (40-60 mm deep) and watered sparingly. After they have sprouted, they should be kept moist. They are not particularly sensitive to drying out, and it is best to err on the dry side than to over water, and particularly not to let them sit in water that cannot drain away.

They do not need to be fertilised, but benefit greatly from the addition of generous quantities of well-rotted organic matter to the soil. If the soil is very poor, the plants can be fed with small amounts of high potash granular or liquid organic fertiliser during the growing season, but over feeding will encourage leaf growth and reduce the number of flowers. It is not necessary to lift the corms every year, but it can be done if required i.e. flowering will not be detrimentally affected if they are lifted every year, and it should be done if the bed they are planted in is going to be irrigated during summer. It is necessary to lift and divide the corms every three to five years, otherwise the plants become overcrowded and flowering decreases. Once the plants are completely dormant (in November-December) the leaves can be removed at ground level or the corms can be lifted and stored in a cool dry place. If they are left in the garden, they should be kept as dry as possible.

Propagation is by seed or division of offsets. Seed is sown in autumn, from April until June, thinly, in deep (min. 10 cm) seed trays, to allow for root development. The soil medium should be well-drained, a recommended mix being 2 parts sand : 2 parts compost : 1 part loam or equal parts sand and compost, and the seeds should be planted 3 - 4 mm deep, covered with clean sand and kept moist and lightly shaded. It is also advisable to protect them from rain during this period. Seed germinates readily within 3 to 4 weeks.

Watering should be reduced towards the end of the growing season and withheld completely when they are dormant. The young corms should be lifted at the end of their first season and stored in dry peat in a cool, dry place to prevent rotting, then replanted in March at a depth of one-and-a-half times their size, and spaced 3 cm apart in order to allow sufficient space for the development of the corms. The young plants should flower in their third season. Although Watsonia marginata does produce offsets (daughter bulbs) it does not produce them as abundantly as other species of Watsonia. When the corms are being lifted for replanting every 3 to 5 years, the corm clusters can be broken apart and replanted. This should be done during the dormant period (December to April) with replanting done in autumn (March to April).

Watsonia is grown as a garden plant in many countries, but it must be noted that it is a declared invasive weed in Australia. Gardeners that are concerned about growing potentially invasive species should contact their local conservation authority for advice or a list of species to avoid.