Geranium or Pelargonium?

Geranium or pelargonium? (Encierro / Adobe Stock)
UCCE Master Gardener

When people talk about geraniums, they can be talking about one of two different plants. The common garden plant most of us know as a geranium (zonal geraniums, scented geraniums, ivy geraniums, etc.) are actually a very similar plant called a pelargonium! 

Geraniums and Pelargoniums are often mixed up because both go by the common name of geranium. ​When pelargoniums were first brought to Europe from South Africa, it was thought they were the same genera plant as the European Geranium. It was later found that although they share many similarities, they differ in several ways. Both remain in the family of plants called Geraniacea, but they were separated into two different genera in 1789. One genus is the geranium; the other is the pelargonium. The goal of this article is to describe the different plants and explain how they are similar or different. 

Geraniums

True geraniums are perennial plants that die back in winter and reappear in spring. Most of them are low growing, spreading plants. They tolerate shade and have delicate foliage. Their flowers can be white, pink, purple, blue, or nearly black, and are symmetrical in shape and color. The flower colors are more muted than the brightly colored pelargoniums, and the petals have veins that are easily visible. Geraniums are considered “hardy” because they survive the winter by dying back or going dormant. Being herbaceous, geraniums have soft stems. Their leaves are circular in form or palmately cleft (think maple leaf). These perennial geraniums are hardy in zones 3-9.

Pelargoniums

Pelargoniums, on the other hand, cannot tolerate cold temperatures, having originated in South Africa where the weather is mild. They do not die back and go dormant in the winter like the true geranium, but stay evergreen. Pelargonium stems are woodier than geraniums. Leaves of pelargoniums are thick and fleshy with a round or lobed shape. Some varieties have a waxy layer which increases their drought tolerance. They can have a dark, horseshoe-shaped pattern on the edges. The flowers come in clusters and in bright colors, including red and orange. The foliage of some pelargoniums is often fragrant, reminding us of peaches, lemons, roses, peppermint, strawberry, nutmeg and apple. Pelargoniums are hardy in zones 9-12. Since they need winter protection, they often do well in pots where they can be protected from cold temperatures. 

Types of Pelargoniums

Zonal pelargoniums are what we most commonly call a garden geranium. They are upright, bushy, and succulent-stemmed, with hairy leaves that often have dark striations and a pungent odor. The single or double flowers form large, spherical clusters in a wide variety of colors, such as red, orange, peach, salmon or white. 

Regal pelargoniums, often referred to as “Martha Washington geraniums,” have large showy flowers that resemble azalea flowers. Colors come in shades of white, purple, pink, red and maroon, some with eye-catching patterns. Mid-green leaves can be rounded, lobed or partially toothed.

Ivy geraniums have a vine-like growth habit that make them very suitable for hanging baskets and window boxes. They have glossy, bright green leaves resembling ivy plant leaves. Their flower clusters come in shades of red, pink, mauve, purple, or white. 

 Scented pelargoniums have strong fragrances of rose, nutmeg, apple, peppermint or lemon. The lemon-scented varieties are often deemed useful in repelling mosquitoes. Their mid-green leaves can be variegated. They bloom in shades of mauve, pink, purple, or white.

Geranium or Pelargonium?

Even though their names are used interchangeably, it is important to understand their differences, especially their growing requirements. The Pelargonium needs winter protection from low temperatures. The geranium will die back in the winter and go dormant. In our Central Valley climate, pelargoniums prefer daytime temperatures between 70-85 degrees, and nighttime temperatures between 55-65. If the temperatures get below 55, it may result in yellowing, wilting and stunted growth. 

The shape of the flowers offers a way of distinguishing between the two genera Geranium and Pelargonium. Geranium flowers have 5 symmetrical petals all the same size and shape. Pelargonium flowers have 5 petals, with the two upper petals different in color and pattern from the three lower petals. 

Pests 

The most common pests of geraniums and pelargoniums are aphids, whiteflies, mealybugs, and spider mites. All these insects suck nutrients from the plants. They excrete excess sugar which provides a source of food for black sooty mold. Spraying the insects with a diluted soap solution can often be all that is needed to wipe out the pests. Mealybugs can be a little trickier as they are covered by a cottony mass and often live where the stem and leaf join. Use a cotton swab dipped in alcohol to knock them out.

There is also a caterpillar known as the geranium budworm (Heliothis virescens) that can cause damage to pelargoniums as well as other garden ornamentals such as roses and petunias. They are active in late summer in the evenings and attack the flower buds. The sure-fire way of getting rid of those is to pick them off. Oils and sprays are not completely effective. Bt, or Bacillus thuringiensis var. kurstaki is a naturally occurring bacterium that kills certain leaf-eating worms and caterpillars. It does not harm other insects and is commonly sold as “Caterpillar killer.”

It is interesting how names of flowers can be confusing. We are most familiar with the Pelargonium, even though we usually call it a geranium! I think I am going to be more careful and call the Pelargonium what it really is, a Pelargonium. But as William Shakespeare famously said: “A rose by any other name would smell as sweet.”

Gardeners will be live to answer your questions on Saturday, May 18, 8 to 11 a.m. at the Visalia Farmers’ Market at its new location, Tulare County Courthouse north parking lot in Visalia; or from 11 a.m. to noon at the Oleander Presentation at Tulare Public Library in Tulare. You can also contact them at 559-684-3325, or visit their web site at ucanr.edu/sites/UC_Master_Gardeners.

This column is not a news article but the opinion of the writer and does not reflect the views of The Sun-Gazette newspaper.

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