Geranium macrorrhizum is quite drought-tolerant once established, making it a low-maintenance choice. During its first growing season, water regularly to ensure proper root development, keeping the soil consistently moist but not waterlogged. Mature plants typically only require supplemental watering during prolonged dry spells or extreme heat. Always allow the top inch or two of soil to dry out between waterings to prevent root rot, especially in heavier soils.

Pruning Geranium macrorrhizum is primarily for tidiness and to encourage fresh growth. After the main flush of flowers in early to mid-summer, shear back the spent flower stalks and any leggy or untidy foliage. This 'Chelsea chop' can promote a second, albeit smaller, bloom and maintain a compact, attractive shape. A more significant cut-back in late summer or early autumn can rejuvenate older, sprawling plants.

Geranium macrorrhizum is remarkably easy to propagate, primarily through division. The best time for division is in early spring or autumn. Simply lift the entire clump, gently separate it into smaller sections, ensuring each piece has healthy roots and at least one growing point. Replant these divisions immediately at the same depth. Softwood cuttings can also be taken in late spring or early summer for rooting in a moist, well-drained medium.

While primarily a garden plant, if grown in containers, Geranium macrorrhizum will eventually need repotting. Repot every 2-3 years in early spring, moving it to a slightly larger pot with fresh, well-draining potting mix. If the plant has become root-bound, you can also divide it during repotting to create new plants. Ensure good drainage to prevent waterlogging, which can be detrimental to its health.