Crop Vignette: Geraniums and Pelargoniums

This first appeared as “Spotlight on Ornamentals: Geraniums? Pelargoniums? What’s the difference?” in the IR-4 Newsletter 45(1):5.

Plant Information

Geraniums and pelargoniums are often confused with each other. And it is very easy to do since the flower is widely grown as a bedding plant and in containers which are known as ‘geranium’, but its Latin genera name is ‘Pelargonium sp.’ The genus Geranium contains 422 species of flowering annual, biennial and perennial plants and are found in temperate regions. Several species are cultivated for horticulture and pharmaceutical uses, but the vast majority of ‘geraniums’ sold in the U.S. are actually ‘pelargoniums’, which is what we will call them in this article.

Pelargoniums are one of the top annual ornamental horticulture crops in the U.S. with over $134 million wholesale value annually (USDA-NASS, Floriculture Crop 2012 Summary, April 2013). Pelargoniums readily germinate from seeds and easily root from cuttings; both avenues of propagation are available with cutting production more common.

Pelargoniums were first cultivated before the 1600s and Pelargonium triste, a native of South Africa, was probably brought to the botanical garden in Leiden, Netherlands on trading ships. John Tradescant purchased seeds in Paris and introduced them to England in 1631. Pelargoniums are native to south, east and northeast Africa, Asia, St. Helena, Tristan da Cunha, Madagascar, Australia and New Zealand. There are 270 species worldwide with the highest diversity occurring in southern Africa with 219 species. Approximately 20 species are the progenitors of thousands of modern pelargonium cultivars

Ivy-leaved pelargoniums are trailing cultivars with P. peltatum as the main contributing species. Regal pelargoniums are known as P. x domesticum and are primarily derived from P. cucullatum and P. grandiflorum. Zonal pelargoniums, known as P. x hortorum and bred primarily from P. zonale and P. inquinans, are highly sought after with over 500 cultivars. Scented leaf pelargoniums are derivatives of a number of species.

Main Disease and Pest Problems

Disease and pest problems can plague pelargoniums. A few of the concerning pathogens include Botrytis, Pythium, Xanthomonas. IR-4 has sponsored research on each of these diseases as well as on geranium rust. Xanthomonas leaf spot on pelargonium was a model system to study the impact of purported bactericides. Out of this research, copper based products consistently exhibited good efficacy, while there were a few products with promise including Citrex, Firewall and Insimmo.

IR-4 has also sponsored research of geraniums with plant growth regulators (PGRs) to enhance shelf life and crop safety to ensure little if any injury occurs with application. The PGR studies were designed to study whether PGRs may help overcome shipping stress, and enhance shelf quality and display life. Products containing 6-BA (Fascination, Maxcel, Exilis Plus) caused no to moderate injury which affected plant quality and shelf life of various cultivars. In general, ivy leaf cultivars like ‘Tutti Frutti’ were more sensitive than zonal cultivars like ‘Tango’. The GA4+7 products (NovaGib and Provide) generally were not phytotoxic and had positive effects in some studies; however, they increased peduncle length at 100 ppm which may be unacceptable.

Geranium and Pelargonium Growing Tips From Gardening Know How

Geraniums (Pelargonium x hortorum) make popular bedding plants in the garden, but they’re also commonly grown indoors or outside in hanging baskets. Growing geranium plants is easy as long as you can give them what they need.

How to Grow Geraniums 

Depending on where or how you grow geranium plants, their needs will be somewhat different. Indoors, geraniums need lots of light for blooming, but will tolerate moderate light conditions. They also need indoor temps of around 65-70 degrees F. (18-21 C.) during the day and 55 degrees F. (13 C.) at night.

These plants need to be grown in well-draining potting soil as well. When growing geraniums outdoors, they require moist, well-draining soil similar to that of indoor potting soil with equal amount of soil, peat and perlite.

Locate your geraniums in an area with at least six to eight hours of sunlight a day. Since these plants must be protected from cold, wait until the threat of frost has passed before planting. Space plants about 8 – 12 inches apart and around the same depth as their original planting pots. Mulching the plants is also recommended to help retain moisture.

Care of Geraniums 

Whether indoors or out, geranium care is pretty basic. In addition to watering, which should be done deeply and once the soil begins to feel dry indoors or at least weekly outdoors (though potted plants may need daily watering in hot weather), fertilizing is usually necessary. Use a water-soluble houseplant fertilizer or a 5-10-5 fertilizer with additional organic matter every four to six weeks throughout their active growing season.

Indoor potted plants may require repotting once they become overgrown, usually noted by wilting between waterings. Regular deadheading of spent blooms will also help encourage additional blooming. When watering outdoor plants, it’s best to avoid irrigation, as this can lead to pests or disease issues.

Geraniums plants root easily from cuttings and can be propagated in fall for overwintering of outdoor plants. They can also be dug up and brought inside.

Sources Cited