From a botanical perspective, Zonal Geraniums are prized for their robust constitution and adaptability to indoor conditions. They possess a distinctive "zone" or horseshoe-shaped band of darker pigment on their leaves, a trait from which they derive their common name. These plants are sun-loving heliotropes; their growth habit and flowering are directly influenced by light availability. For optimal indoor growth, they require a south or west-facing window with at least 4-6 hours of direct sunlight daily. Without sufficient light, they will become leggy (etiolated) as they stretch for a light source and may refuse to bloom. Their thick, succulent-like stems are an adaptation for water storage, making them moderately drought-tolerant. This means indoor gardeners should allow the soil to dry out slightly between waterings to prevent root rot, a common fungal issue in constantly moist potting media.
Ivy-Leaf Geraniums present a different growth strategy, characterized by their trailing or cascading habit and glossy, ivy-shaped leaves. This morphology makes them an excellent choice for hanging baskets indoors. Botanically, their vining nature is an adaptation to seek new ground and maximize light capture in their native habitats. Indoors, they will readily trail several feet, but their flowering is heavily dependent on high light intensity. They perform best in very bright, direct light. Their leaves are thinner than those of Zonal types, indicating a slightly lower tolerance for drought. Therefore, the potting medium should be kept more consistently moist (but not waterlogged), especially during active growth and flowering periods. Providing a trellis or allowing them to cascade can satisfy their natural growth pattern and prevent stems from becoming tangled.
This diverse group is cultivated not primarily for their often-inconspicuous flowers, but for the fragrant essential oils contained in glandular trichomes (hair-like structures) on their foliage. Brushing against the leaves ruptures these trichomes, releasing scents ranging from rose and lemon to mint and nutmeg. From a plant health standpoint, these oils may serve as herbivore deterrents. For indoor cultivation, their cultural requirements are similar to Zonal Geraniums: they demand bright light and well-draining soil. However, they are often more forgiving of lower light levels than their flowering cousins, though insufficient light may reduce the potency of their scent. Pinching back the growing tips is a crucial practice; it encourages a bushier, more compact form by promoting axillary bud break, which prevents the plant from becoming sparse and woody at the base.
Also known as Martha Washington geraniums, Regals are the most demanding from a cultural perspective. They are celebrated for their large, spectacularly patterned flowers that often resemble those of azaleas. Botanically, they have a specific growth cycle. They require a distinct cool dormancy period (55-60°F or 13-15°C) in winter to set buds for a prolific spring bloom. Without this cooler rest, they will often fail to flower satisfactorily. Furthermore, they are highly susceptible to root diseases if overwatered, especially during their dormant phase. Indoor growers must provide the brightest possible light and excellent air circulation to mimic their preferred conditions. Their large, soft leaves lose water more readily than other types, so they require consistent moisture during active growth but significantly less during dormancy.
