Pelargonium × hortorum, also called garden geranium, is a hybrid species between P. zonale and P. inquinans of the Pelargonium family frequently grown as ornamental plants for cultivating in pots, hanging baskets, and balconies or planted outdoor in gardens. These are the most commonly sold by horticulturists and florists.
This group of plants originates from two wild species from South Africa that were collected and sent to France in 1689. Traces of their cultivation have been found in England in the Duchess of Beaufort’s gardens, who later published an illustrated catalog of her plant collection in 1699. It was introduced to Northern America in 1786 and is now common in several parts of the world.
They were first described by Jan Commelijn, a Dutch botanist, and later described by Carl Linnaeus in his Species Plantarum. Since then, several varieties and hybrids became popular with gardeners, who started calling the variety “geraniums”. They have been cultivated commercially for more than two hundred years.
These varieties grow to 24-inches high and wide while trailing or ivy varieties can grow 48 inches long if not pinched back or pruned. The flowers have five petals placed around the center. The colors of the flowers include varying shades of pink, red, scarlet, and white, while orange and yellow varieties have been recently developed.
The flowers bloom on long rigid stalks that emerge from the tips of stems so that the flower head stands above the foliage. Flowering starts from spring until autumn without interruption. The entire plant, except the flowers, has a distinctive smell. They grow about 9-12 inches a year and while they can live for some time, older plants don’t flower as abundantly unless drastically pruned in late autumn.
These plants need 4 or 6 hours of bright sun in the morning and light shade in the afternoon.
These plants prefer to be kept reasonably moist, so water outdoor plants every 2 or 3 days. Plants growing indoors need watering 2–3 times weekly in summer, while those growing outdoors under full sun need watering every day, in the morning or evening, and never at noon.
Plants growing in the ground should wait for the top level of the soil to slightly dry in between watering to avoid contracting root rot. The potted plants must have good drainage to remove excess water to prevent root rot. Over-watering is the most common cause of plant death.
They prefer going without water for some time than sitting in waterlogged soil. A good sign of under-watering or over-watering is yellowing foliage. However, avoid under-watering, since the constant revival of wilted plants will result in poor flower production which might also cause leaf drops.
While these plants are recognized to tolerate different humidity levels, they generally prefer well-ventilated spaces and dry environments. In very humid regions, rust and mildew might occur.
These plants aren’t cold hardy and prefer daytime temperatures between 50-75°F and nighttime temperatures of 50-60°F
These plants don’t like heavy, clayey soils and prefer loose soils with good drainage capacities such as peat or loamy soils, with a pH of 5.8-6.3. If your soil is heavier or clayey, amend it with peat, perlite, and/or compost. With suitable soil and good watering, your plants will thrive and be healthy.
If the soil lacks nutrients, incorporate organic material such as bark, compost, and manure to help improve it.
While these plants like being root-bound, they need repotting when the roots cannot absorb water or when the plants keep wilting even after watering. Prepare a larger new container filled with loose, well-draining soil. Prune the stems and branches back about 4 inches and remove the plant from its old flowerpot. Transfer the plant to the prepared flowerpot, holding it while you add soil around the roots.
These plants are easy to propagate through seeds, cuttings, and division. However, division or stem cuttings are the most used since seeds can be difficult to find.
Cuttings can possibly be started in moist soil or water. While this is usually done in spring, it is possible to accomplish this throughout the year. Choose healthy stems and take a nice, healthy cutting. Plant it either in water or suitable soil until the roots develop. They are then ready to transplant to containers or the garden.
After a year or two of growth, new shoots will emerge from the plant’s base. Wait till the stems grow a few inches then carefully separate the stem with the roots and replant in suitable soil.
While these plants like an occasional light dose of fertilizer (water-soluble fertilizer is best), over-fertilizing hurt flower production since only the foliage will benefit. Potted plants with soil rich in nutrients need light fertilizing every 4 or 6 weeks only in spring and summer.
If your plants grow in milder winters, they will continue to flower and feeding must now be reduced to once every 8 weeks.
Plants growing outside generally don’t need pruning unless growth is spindly or unkempt. However, deadheading old flowers will help increase flower production and prevent diseases. Remove any yellowed or dry leaves that are usually found near the plant’s base.
The common pests that attack these plants are aphids, whiteflies, and slugs or caterpillars. The most destruction is caused by caterpillars that eat and damage the leaves and flowers. The most efficient way to remove them is by hand or using a pesticide.
The worst caterpillars are budworms that tunnel their way into flower buds and attack undeveloped petals, affected flowers display shredded or petals full of holes when they bloom, with the majority of affected flowers often rotting before they bloom. These pests are hard to eliminate or control because pesticides cannot penetrate inside the buds.
Whiteflies typically attack the leaves in summer and are usually found underneath the plant’s leaves. Use a suitable pesticide to treat the plants.
These plants are predisposed to fungal diseases that generally start on old or dead flowers; any old or dead flowers must be regularly removed by cutting off the stalks at the base.
Alternaria leaf spot creates dark, circular, and mushy spots with yellow borders on leaves. They range from ¼ to ½-inch in diameter. Treat this disease by applying a suitable fungicide.
Bacterial blight appears as brown or tan irregular or round water-soaked spots or lesions. They might also appear in yellow wedge-like areas, with the tip of the wedge touching the leaf’s vein. In severe cases, if the blight has not been contained, the foliage might wilt with the stems rotting, and eventually, it will kill the plant. Infected plants have to be removed before the infection can spread.
Botrytis blight or gray mold is common during spells of cool, damp weather, usually affecting the flowers first by causing the flower to turn brown and becoming covered by grey fungus spores. The infected flowers will prematurely fall off and any leaves coming into contact with the infected petals will also develop spots or lesions. The only method of dealing with this is to prune infected plant parts and destroy them to remove any debris around the plant. If you can spot the blight early, suitable fungicides can be applied to control further spread.