"Most people know them as simply "geraniums", those red, pink or white flowering plants with thick pleated leaves that look so good in pots and window boxes. They are one of the most popular container plants, yet they are not really geraniums at all. Botanically they are Pelargonium. How's that for a mouthful? There are true geraniums, the perennial cranesbills, but they look little like the annual plants we commonly call geraniums.
The confusion with the names can be traced back to disagreements between botanists over classification and is of little importance to most gardeners, except for the distinction that perennial cranesbill geraniums will come back each year and zonal geraniums, those now classified as Pelargonium, are topical perennials usually grown as annuals. They got the prefix "zonal" because of the markings on their leaves.
Zonal geraniums were discovered in South Africa and if you have a similar, tropical climate, you can grow them as perennials. Along with zonal geraniums, there are 3 more commonly grown types of Pelargonium:
- Ivy-Leaf Geranium (Pelargonium peltatum) – As their name implies, these geraniums have a trailing habit and ivy-shaped leaves. The flowers are smaller and less showy than zonal geraniums and the plants are often used as spillers in containers.
- Scented-Leaf Geranium (Pelargonium domesticum) – Scented geraniums get their fragrance from the oil in their leaves. They can mimic all kinds of scents, like lemon, rose, mint, pine, fruits, and even chocolate. The flowers tend to be small and often insignificant and the leaf shapes will vary. Besides their ornamental and fragrant appeal, many can also be used in cooking.
- Regal and Angel Geraniums (Pelargonium domesticum) – The Regals, also referred to as Martha Washington geraniums are full, bushy plants with flowers in unusual colors and
Zonal geraniums are bushy plants, mainly used for containers and bedding. There has been considerable breeding done, particularly for size and abundance and colors of flowers, so there is a good deal of variety.
- Leaves: Oval leaves grow on succulent stems. The leaves often have zones of maroon or bronzy-green.
- Flowers: Flowers can be single (5 petals) or double and come in clear white, pink, salmon, orange, red, magenta, lavender, and bi-colors.
Pelargonium x hortorum
Geranium, Zonal Geranium
USDA Hardiness Zones 9 -12. Zonal geraniums are basically tropical perennials. Although they are often grown as annuals, they may over-winter in zones as cool as Zone 7, if they have some protection and the winter is mild.
Full sun to partial shade. They will bloom best in full sun.
Mature Plant Size
Size will vary with variety. There are some dwarf geraniums that will never get more than 5 - 6 inches tall and newer varieties being bred for height and spread. In general, most are between 5 - 24 inches (12 - 60 cm) H x 12 - 15 inches (30 - 38 cm) W.
Zonal geraniums start blooming in mid-spring and will repeat bloom until frost. Deadheading the entire flower stalk after the flower fades will encourage more blooms.
Geranium Growing Tips
Soil: Zonal geraniums are not terribly fussy about soil pH, but prefer a slightly acid soil of about 5.8 to 6.5
Planting: You can start zonal geraniums from seed, cuttings or transplants.
Taking cuttings was the traditional method of propagating geraniums and maintaining favorite varieties. If you choose to take cuttings, make sure you only use healthy, vigorous plants.
Starting Geraniums from Seed: Geranium can easily be started from seed, although the seed is usually for F1 hybrids. Seed geraniums are bred to be disease resistant and to bloom well in the heat of summer.
Start seeds 8 - 10 weeks before your last frost date. They can take up to 2 weeks to germinate and should be kept warm, 70̊ and 75̊F (21̊ - 24̊C), and moist in the process. Scarifying the seed before planting will help aid germination.
Harden off young plants before planting outdoors. They should begin to bloom about a month after being set out.
Caring for Geranium Plants
Zonal geraniums are not heavy feeders, but since they are usually grown in containers, a light feeding with your favorite fertilizer, every 2 - 4 weeks, will keep them vigorous.
Stressing the plants slightly by watering only after the soil has been sitting completely dry for a day or two seems to encourage more profuse blooming. Just don't leave them dry for so long they start dropping leaves and declining.
If you don't live in USDA Zone 9 or higher, your plants will need some winter protection. You can bring them in and grow them as houseplants, in a bright, direct light window. You could take cuttings in mid-summer and bring these smaller plants indoors, or you can over winter your geraniums in their dormant state.
Pests & Problems of Geraniums
There are a few fungal and bacterial diseases to look out for, mainly:
- Stem or root rot caused by poorly drained soil.
- Gray mold or botrytis, which causes grayish fuzz on the leaves and eventually a slimy mush, especially in humid or damp weather.
Special thanks to the National Garden Bureau which named Pelargonium its 2012 Plant of the Year and provided research for this article.
Using Geraniums in Garden Design
Zonal geraniums have gotten a bad reputation by plant snobs. They've been considered garish and common. Too many of the brightly colored plants can start to look over the top, but these plants are excellent in all kinds of containers. The brighter reds are very elegant all alone and pair well with flowers in equally bright colors, like portulaca or nasturtium.
Suggested Varieties of Geraniums
- "Appleblossom Rosebud" - Pom-pom flowers in a pink and white bi-color.
- "Black Velvet Rose" - Dark, chocolate-brown leaves with only a narrow band of green and bright rose-pink flowers.
- "Calliope Dark Red" - a cross between zonal and ivy-leaved, with double, dark-red flowers.
- "Divas Orange Ice" - an F1 hybrid with bi-colored white and soft orange flowers that look like creamsicles.
Every year there are more and more choices. If you find a good source to order from, there are Pelargoniums that are tulip-flowered, cactus-flowered and some with spiky star-shaped flowers. There are also the fancy-leaved varieties, grown more for their variegated and patterned foliage.