Zonal Geranium

Zonal geraniums are raised as annuals, either direct-sown or started from seed and transplanted once the hard seed coat has been nicked or otherwise compromised; germination follows within about two weeks at roughly 20°C, and young plants are set out in beds and containers once spring frost has passed.

They grow best in full sun, needing six or more hours of light daily, though afternoon shade helps where summers turn very hot. Soil or potting mix should be fertile and well-drained; water only once the top inch has dried, since the plants tolerate mild dryness far better than constantly wet roots. A slow-release fertilizer at planting sustains growth, and light feeding every two to six weeks during active growth keeps flowers coming, though feeding is best paused during prolonged heat above 90°F to avoid fertilizer burn.

Regular deadheading and pinching keep plants bushy and speed rebloom, and new plants are readily started from stem cuttings rooted in moist, well-draining medium. Before the first freeze, plants can be cut back and brought indoors to overwinter in a bright, cool location, then replanted the following spring.

Zonal geraniums are relatively untroubled by pests, though aphids, spider mites, whiteflies and tobacco budworm can appear, the sap-feeding insects treatable with neem oil or insecticidal soap.

In wet or humid weather, botrytis blight (gray mold), powdery mildew and leaf spots can develop; once botrytis takes hold in a flower cluster it is difficult to eliminate, so affected blooms and leaves are best removed promptly and air circulation improved. Overwatering or poor drainage brings on root rot and yellowing leaves, so well-drained soil and cautious watering remain the main safeguards.

Zonal geraniums are grown almost entirely as ornamentals, valued for containers, hanging baskets, window boxes, garden borders and mass bedding displays, as well as for indoor use in bright rooms. Their flowers also draw pollinators such as bees and butterflies into the garden.

Zonal geraniums descend from South African species, chiefly Pelargonium zonale and P. inquinans, whose seeds were carried from Africa to the botanical garden at Leiden in the Netherlands during the 16th century. Within a few years the plant had spread to the British Isles, France, Italy and Spain, later reaching the Caribbean and, by the 17th century, North America. Hybridization between these southern African parent species produced Pelargonium × hortorum, the group now grown worldwide as the zonal geranium.