Zonal geranium (Pelargonium hortorum) is an annual plant species that looks similar in appearance to other geraniums. The zonal geranium can be distinguished by its zone of red, blue or purple stripping through the middle of the leaf. This species is typically a one-season bloomer, unlike other geraniums that are perennial growers and bloom year round. Zonal geranium blooms come in a variety of colors that include red, pink, burgundy, salmon and white.
I. Appearance and CharacteristicsÂ
Pelargonium × hortorum, commonly called zonal geranium, or garden geranium, is a nothospecies of Pelargonium most commonly used as an ornamental plant. It is a hybrid between Pelargonium zonale and Pelargonium inquinans.
The specific epithet hortorum is a genitive plural form of the Latin “hortus” (“garden”) and therefore corresponds to “horticultural”. The name was created by the American botanist Liberty Hyde Bailey who in 1914, writes “The large number of forms of the common geranium, derives from the variation and probably the crossing of P. zonale and P. inquinans (and possibly others) during more than a century of careful selections”.
It is important to distinguish the botanical Latin term “Geranium”, the extent of which has varied according to botanical knowledge over the centuries, and the vernacular name of French origin “geranium”, whose extension is defined by several centuries of use by amateur and professional gardeners.
Most plants commonly called geraniums by florists and gardeners do not belong to the genus Geranium (as currently delimited by botanists) but to the genus Pelargonium. Currently, most gardeners, amateur or professional, know perfectly well that the geraniums that decorate the balconies are Pelargonium but they are reluctant to use the term they find too pedantic. The term is not felt to be fully part of the common language and still remains marked as scholarly.
They are stocky and large. The flowers can be single or double, and have five petals positioned regularly around the center. The leaves are often fragrant. The flowers come in many colors, including red, shades of pink, scarlet and white. Recently, orange and yellow cultivars have been developed. The inflorescence is carried by a long rigid peduncle, starting from the armpit of the upper leaves, so that the flowered head stands out clearly above the foliage.
Many cultivars have been grown since the late eighteenth century. Cultivars with very double flowers and no anthers are called Rosebud Pelargoniums since the flowers never open completely and therefore resemble a rose. Leaves of circular shape (7 cm in diameter) and have a winged venation and a leaf margin. The blade is covered by a dark annular area, more or less visible depending on the variety. The zoned geraniums are very floriferous plants, not quite demanding when it comes to water. Flowering occurs without interruption from spring until the last days of autumn.
Availability includes the usual nursery “seed-grown” and the “cutting grown” types, which can easily be propagated at home by cuttings and planting side branches. Bracts on cuttings are to be removed, because they often rot. Rooting continues in good conditions for up to 3 weeks. Recently, there are varieties that can be propagated from seeds. Sown in a sandy substrate, it easily germinates at a temperature of 16–18 °C. Zonal geraniums grow in U.S. Department of Agriculture hardiness zones 9 through 12. Zonal geraniums are basically tropical perennials and they overwinter in zones as cool as zone 7.
The whole plant with the exception of flowers gives off a characteristic smell. It blooms for a very long time (throughout the summer) and abundantly, however, most cultivated varieties do not produce seeds. During the year, it grows about 25–30 cm. It is a long-lived plant, however, older specimens become unkempt, because they are fattening with the bottom of the leaves and bloom less well.
It is grown as an ornamental plant, mainly as a potted plant in apartments and in various types of containers on balconies, window sills and verandas. The advantages of this plant are the long-blooming flowers and decorative leaves. Recently, in the composition with other plant species, it is sometimes also grown as a bed plant. The plant needs strong light and some direct sunlight. It prefers a dry atmosphere and a lot of space. It should not be sprayed, as it causes root rot. The peat soil or loam soil is the best substrate. Tilled in the apartment in the summer tolerates well room temperature, in winter it is better to take it to a colder room with a temperature not exceeding 16 °C. In summer, the plant indoors must be watered 2–3 times a week, whilst the geraniums growing in the field in full sun must be watered every day, morning or evening.
II. How to Grow and Care
Zonal geranium thrive when provided with ample sunlight and regular watering; however, they are particularly sensitive to overwatering which can cause root rot. They benefit from well-draining soil and occasional fertilization during the growing season. Deadheading spent flowers promotes further blooming and maintains the plant’s visual appeal.
Sunlight
Zonal geranium thrives under full sun exposure, which maximizes its growth, health, and vibrant flowering. It relishes in at least 6 hours of direct sunlight per day but can also tolerate partial sun. Insufficient light may lead to spindly growth and reduced blooming. In strong light, zonal geranium’s foliage may develop darker zones, indicative of its adaptive response. When planting outdoors, choose a sunny site. For indoor growth, south-facing windowsill is ideal. However, extended periods of shade can hinder flower production and weaken the plant.
Temperature
Zonal geranium are native to the Cape of Good Hope in South Africa, so they like mild and cool climates. The suitable temperature range for growth is 5 to 25 ℃, and the optimum temperature is 15 to 20 ℃. The relative air humidity should be no higher than 75%, and excessive temperatures and humidity should be avoided.
Watering
Originating from arid regions, zonal geranium has adapted to thrive with minimal moisture, exhibiting a preference for drier conditions. This species maintains its hydration balance by storing water in its tissues, allowing it to withstand periods of drought. Regular watering every week will suffice to meet its needs without over-saturating the soil. As an outdoor plant that flourishes in sunny environments, zonal geranium benefits from well-draining soil that mimics its native habitat’s dryness, ensuring excess water doesn’t linger around its roots.
Soil
Zonal geranium thrives in well-draining soil to avoid water-logging, which can lead to root rot. A mix of two parts potting soil, one part peat, and one part coarse sand or perlite ensures proper aeration and drainage. If peat is unavailable, coco coir is a sustainable alternative. To boost growth, incorporate a slow-release fertilizer at planting time and supplement with liquid fertilizer during the growing season following package instructions. Regular checks for soil moisture are important to maintain ideal conditions for zonal geranium.
Fertilizing
Fertilize zonal geranium biweekly with high phosphorus fertilizers to bolster bloom production and fortify root health. Apply half-strength doses to prevent overfertilization, ensuring zonal geranium’s vibrant growth. During dormant winter months, reduce feeding to monthly. Gradually resume regular fertilization as spring growth begins. Always water zonal geranium before fertilizing to guard against root burn and facilitate nutrient uptake. Seasonal adjustments and measured application are key for zonal geranium’s flourishing.
Pruning
After fall, depending on the growth of zonal geranium, keep just 3-5 strong main branches that are close to the base and evenly distributed. Cut the remaining slender and weak branches directly from the base. Only strong lateral buds should be left on the branches, and the rest should be cut off. About five days after pruning, new, neat branches will germinate and produce flowers later.
Propagation
Generously known for their vibrant clusters of flowers and varied leaf patterns, zonal geranium can be propagated effectively through division, enabling gardeners to multiply their colorful displays. By splitting the rootball into smaller, well-rooted sections with care, each division can be potted individually and encouraged to flourish into a separate, full-fledged plant. This method relies on the plant’s natural tendency for producing dense foliage and roots, allowing divisions to quickly establish themselves when provided with ample moisture and indirect light.
Transplanting
For zonal geranium, it’s best to transplant during early to late spring or mid-fall to early winter, providing optimal growing conditions. Choose a location with well-drained soil, plenty of sun, and good airflow to encourage healthy growth. Remember, a gentle touch while transplanting is appreciated by these plants!
Overwintering
Zonal geranium originates from the warm climates of South Africa. Winters put it into dormancy, a result of its adaptive cycle. To ensure zonal geranium’s health during colder months, keep it indoors with temperatures above 50°F, provide plenty of light, and water sparingly but regularly. Fertilize lightly, as zonal geranium will not develop much in winter. This balanced overwinter care keeps zonal geranium vibrant, preparing it to bloom beautifully in spring.
Repotting
Repot zonal geranium in early spring, every 2-3 years, to accommodate its moderate growth as a bushy plant. Select a container 1-2 inches larger in diameter to allow for healthy root expansion. Post-repot, use well-draining soil and maintain consistent moisture without waterlogging. Ensuring plenty of light and gentle handling of roots during repotting will promote vigorous growth and flowering.
III. Uses and BenefitsÂ
Often used as a cover and edging plant because of its bright blooms and heavy growth patterns, the zonal geranium is the most common form of geranium and is prized for its bright blooms and easy growth. It is used for borders as a way to create a pop of color in the landscape. They are seen in gardens of all types, as they do well in any sunny spot and are low fuss. Because they deter many common pests, they are often planted around vegetable gardens or near rose bushes to protect those plants.
IV. Harvesting and Storage
Zonal geranium are self-pollinating plants. After their petals fall, there will be a 3 cm long, green, needle-shaped pod with a few seeds in the middle of the calyx. The mature seeds are dark brown and have white hairs, and can be harvested for preservation.
The bloom time of zonal geranium is relatively long. Fresh flowers can be cut at the scape base with sharp gardening scissors in the evening. Cut the base at a 45° angle to increase the water absorption area, and cut off excessive leaves to reduce water evaporation. Quickly put flowers in a vase with clean water to prevent water loss.
