The flowering perennial plants known collectively as hardy geraniums comprise many cultivars of several different species and hybrids within the Geranium genus. As a group, they are also known as true geraniums, perennial geraniums, or wild geraniums. Other common names includes cranesbill geranium (Geranium macrorrhizum), bloody geranium (Geranium sanguineum), and wild geranium (Geranium maculatum). Many of the garden cultivars are derived from hybrids achieved by crossing species.
There is a great deal of variety in the Geranium genus, but most of the commonly grown species are low growing, dense, carpet-like plants with flower stalks that poke and weave through neighboring plants. The flowers float on top of the plant in shades of white, pink, magenta, purples, and blues. The flowers are small—around one inch—and cupped-shaped, attracting plenty of butterflies and bees.
Hardy geraniums can be used in a variety of ways in the landscape, depending on the type. Some varieties make good border plants, others are ideal for woodland gardens and part shade locations, while others are excellent ground cover or rock garden plants. A few hardy geraniums bloom just once, usually early in the season, but most will start blooming in mid-summer and repeat bloom sporadically throughout the growing season. Newer varieties, like 'Rozanne' bloom non-stop all summer.
|Botanical Name||Geranium spp.|
|Common Name||Geraniums, perennial geranium, wild geranium, cranesbill geranium, bloody geranium|
|Plant Type||Flowering perennial|
|Mature Size||6 to 24 inches tall|
|Sun Exposure||Full sun to part shade (varies according to variety)|
|Soil Type||Medium moisture, well-drained soil|
|Soil pH||5.8 to 6.3|
|Bloom Time||Spring, summer, fall (varies according to variety)|
|Flower Color||Blue, pink, purple, white|
|Hardiness Zones||3 to 9 (varies according to variety)|
|Native Area||Temperate regions worldwide, especially Mediterranean|
How to Grow Hardy Geraniums
With many varieties derived from several different species, hardy geraniums vary in their care needs, depending on the type you are planting. Generally speaking, though, hardy geraniums prefer well-drained, moderately rich soil. Most will do well in either full sun or part shade, but they like to be fairly dry—they can become prone to mildew if kept damp.
Plant hardy geraniums so that the crown of the plant is at ground level or slightly above. Planting too deep can prevent them from flowering. Cutting them back after flowering is complete often prompts a second bloom period later in the summer.
Hardy geraniums are relatively trouble-free plants. Slugs may attack young geranium plants, while mildew and rust can infest foliage, especially in partial shade and/or humid climates. Shearing back and disposing of the infected leaves will help.
Hardy geraniums accept a wide range of exposure conditions. For the best flowering and most vigorous geranium plants, site them in full sun to part shade. If geraniums are grown in hot, full sun, provide regular water. Some varieties of geraniums can tolerate full shade, but they likely won't blossom as fully as those that have plenty of sun.
Geraniums are not particular about soil pH, but a neutral to slightly acidic soil is ideal. Most prefer medium-moisture, well-drained soil, though some species prefer relatively dry soil.
Geraniums are a low-maintenance plant, so water them only when the soil gets dry. If located in full sun, water the plant more frequently. Hardy geraniums can become prone to fungal disease if watered overhead.
Temperature and Humidity
Hardy geraniums grow best in daytime temperatures between 65 and 75 degrees Fahrenheit and nighttime temperatures between 50 degrees and 60 degrees. They tolerate a wide range of humidity levels, though mildew and rust can be a non-life-threatening issue in very humid regions.
Unless the soil is very poor, hardy geraniums generally do fine with no feeding other than a yearly application of compost. Poor soils may require a spring feeding with a time-release balanced fertilizer.
Propagating Hardy Geraniums
Most species of hardy geranium live longer if divided every 3 to 5 years, though you can divide more frequently to keep them from spreading or to obtain new plants. Once you see the center dying out, it is definitely time to divide.
Divide the geraniums in the early spring to early summer, giving the plant time to establish its roots before a frost. To divide the plant, dig it up and shake the soil off the roots. Use a trowel or a knife to separate, making sure that each division has a root section and leaves. Replant each divided section at the original depth, and water the plants well.
Many hardy geraniums will self-seed very readily, even taking root in sidewalk cracks. They do not spread uncontrollably, though, so they are rarely a problem in the garden. The volunteer seedlings can be easily dug up and transplanted elsewhere.
Varieties of Hardy Geraniums
There are as many as 300 types of geraniums available to grow, including:
- Geranium × oxonianum 'Wargrave Pink': The most commonly grown geranium with salmon-pink flowers, it grows 18 to 24 inches tall in zones 3 to 8.
- Geranium 'Gerwat' ROZANNE: A violet-blue hybrid that flowers almost non-stop throughout summer. it grows 18 to 24 inches tall in zones 5 to 8.
- Geranium 'Ann Folkard': This is one of the earliest blooming geraniums with magenta flowers that repeat bloom throughout the season. This hybrid has a trailing habit and grows 6 to 8 inches tall in zones 5 to 9.
- Geraniu'Double Jewel': Double-white petals feature a lilac center. It’s short and perfect for containers, as it grows 10 inches tall in zones 4 to 8.
- Geranium 'Southcombe Double': Double, pure pink blooms resemble fluffy asters. It grows 10 inches tall in zones 4 to 8.
- Geranium 'Johnson's Blue': This variety is thought to be a hybrid between G. himalayense and G. pretense. It is one of the popular of all varieties, growing about 18 inches tall with sky-blue flowers. It is suitable for zones 4 to 8.
Hardy geraniums require little care, once established. The plants can get a bit scraggly after blooming and deadheading is difficult with so many wispy stems. Shearing the plants back to basal growth will improve their look and encourage reblooming. The plants fill back in within weeks. The exception is Geranium macrorrhizum, which is easily deadheaded and needs no shearing.