Growing Zonal Geraniums
Overview and Description
We know them as simply "geraniums". 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 cransbills, but they look little like the annul 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 cransbill 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:
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.
Botanical Name:Pelargonium x hortorum
Common Name:Geranium, Zonal Geranium
Hardiness Zones: 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.
Sun Exposure: Full sun to Partial Shade. They will bloom best in full sun.
Mature 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.
Bloom Period: 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.
Design Suggestions: 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.
The softer pinks and salmons complement blue and purple flowers and the lavender shades really stand out next to the chartreuse foliage of Huechera or sweet potato vines.
Soil: Zonal geraniums are not terribly fussy about soil pH, but prefer a slightly acid soil of about 5.8 to 6.5. (It's essential that the soil be well draining - these plants don't like to be wet for long!)
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.
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 them slightly by watering only after the soil has dried out completely for a day or two seems to encouraging 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:For the most part, zonal geraniums are not prone to insect pests, when grown outdoors. Indoors, aphids and whiteflies can become a nuisance.
There are a few fungal and bacterial diseases to look out for, mainly
Special thanks to the National Garden Bureau which named Pelargonium its 2012 Plant of the Year and provided research for this article.
BY: MARIE IANNOTTI
Black Leg Disease
Black Leg of Geranium
M. Grabowski, UMN Extension Educator
Black leg is a stem infection of Geraniums (Pelargonium spp.) that results in a distinctive black discoloration of stems. As infected stems rot, they become soft and often bend over. This disease is caused by several species of the water mold Pythium. Pythium spp. are soil dwelling organisms that thrive in wet conditions and can survive in infected plant debris and soil. Black leg symptoms often start at the soil line and move up the plant.
To avoid black leg, inspect all geraniums prior to purchase and select only healthy symptom free plants. If repotting geraniums, use new clean potting mix and new pots or pots that have been cleaned with a solution of 10% household bleach. Take care to keep tools, watering cans, and hose heads off the floor and away from dirt and plant debris. Pythium spp. can be introduced into clean potted plants by tools that have contacted contaminated dirt or plant debris. Do not over water plants.
If plants do become infected, they will not recover. Discard the plant and the potting mix. Clean the pot with a solution of 10% household bleach before reusing it.
Source: Black Leg
Posts are made by Brenda Archer or Sharon Pearce - both are past Presidents of the San Diego Geranium Society!