Zonal Geraniums (Pelargonium x hortorum)

Zonal geraniums (Pelargonium x hortorum) are a popular type or group of Pelargonium cultivars, with leaves marked with a brown annular zone and inflorescence in the form of large balls of tight flowers, usually red, pink, or white. These are the most common geraniums of garden centers and florists, sold in pots for windowsills and balconies or planted in flowerbeds. Zonal geraniums are complex hybrids which have P. zonale and P. inquinans as dominant parents.

Hybrids are available in both F1 seed varieties (single flower types that flower the first year from seed and come true from seed) and vegetative varieties (semi-double to double types that are propagated by cuttings). Zonal geraniums can be tricky to grow well in hot and humid summer climates with periodic hard rainfall.

Physical Characteristics

• Leaves: The leaves are thick, succulent and are usually round to kidney-shaped. One of their most defining features is the “zonal” pattern in the center of each leaf, from which they derive their name. This pattern typically consists of dark, circular markings or bands that radiate outwards from the center of the leaf. The color of these markings can vary from dark green to burgundy, and they often contrast sharply with the lighter green background of the leaf.
• Stems: The stems of zonal geraniums are usually succulent and semi-woody. They can be upright or slightly trailing, depending on the variety and growth habit.
• Flowers: Zonal geraniums produce large clusters of flowers in various colors, including red, pink, white, salmon, lavender, and bi-colors. The flowers are typically semi-double or single and have five petals. They bloom profusely throughout the growing season, especially in full sun conditions.
• Growth Habit: Zonal geraniums are herbaceous perennial plants but are often grown as annuals in cooler climates. They have a bushy, compact growth habit and can reach heights of 12 to 24 inches (30 to 60 cm) with a similar spread. Some varieties may have a more trailing or spreading growth habit, making them suitable for hanging baskets or container plantings.
• Root System: Zonal geraniums have fibrous root systems that spread out horizontally in the soil. They prefer well-drained soil and can be susceptible to root rot if overwatered.
• Fragrance: Some varieties of zonal geraniums have fragrant leaves, especially when brushed against or crushed. The fragrance can vary from citrusy to spicy, depending on the cultivar.

How to grow and care for Zonal geraniums

USDA Hardiness Zones and suitability of growing Zonal geraniums

Planting Location

• Geraniums prefer full sun but can tolerate partial shade, especially in hotter climates.
• Ensure the planting location has well-drained soil to prevent waterlogging, as geraniums are susceptible to root rot.

Planting Time

• In cooler climates, plant geraniums after the last frost date in spring.
• In warmer climates, geraniums can be planted in fall or winter for winter and spring bloom.

Soil Preparation

• Use well-draining soil with a pH of 6.0 to 7.5.
• Incorporate organic matter like compost into the soil before planting to improve drainage and fertility.

Planting

• Dig a hole slightly larger than the root ball of the geranium.
• Place the plant in the hole and backfill with soil, gently firming it around the plant.
• Space plants 12 to 18 inches apart, depending on the cultivar.

Watering

• Water geraniums thoroughly after planting and keep the soil evenly moist until established.
• Once established, allow the soil to dry out slightly between waterings. Avoid overwatering, as this can lead to root rot.

Fertilizing

• Feed geraniums with a balanced fertilizer (10-10-10 or similar) every 4 to 6 weeks during the growing season.
• Avoid excessive fertilization, as it can lead to leggy growth and fewer flowers.

Pruning and Deadheading

• Pinch back young geranium plants to encourage bushy growth.
• Deadhead spent flowers regularly to promote continuous blooming.
• Remove yellowing or dead leaves to improve air circulation and reduce disease risk.

Overwintering (for colder climates)

• In regions with frost, geraniums can be overwintered indoors.
• Before the first frost, dig up geranium plants from the garden and pot them in containers.
• Place the containers in a cool, sunny location indoors and water sparingly during the winter months.

Pest and Disease Control

• Monitor plants regularly for pests such as aphids, spider mites, and whiteflies. Use insecticidal soap or neem oil to control infestations.
• Keep foliage dry to prevent fungal diseases like powdery mildew and botrytis. Water at the base of the plant, avoiding overhead watering.

Propagation

• Geraniums can be propagated from stem cuttings or by division.
• Take stem cuttings from healthy, non-flowering shoots and root them in moist potting soil or water.
• Divide established plants in spring or fall by carefully separating the root ball into sections with a sharp knife.

Cultivars of Zonal Geraniums