For over 300 years geraniums have been one of the most popular decorative plant for indoor and outdoor use. Common garden geraniums come in every flower color except blue and yellow. They can be grown as bedding plants, in containers on decks and patios, in hanging baskets or in window boxes.

To see how many of the new varieties of geraniums and other annual flowers perform under Colorado’s rough clay soil, brutal wind and intense sun visit the Colorado State University Annual Flower Trial Gardens. Plants in these gardens, located near the CSU campus at the northeast corner of College Avenue and Lake Street in Fort Collins, are in peak bloom during July and August.

There are two different groups of plants known as geraniums. The showy flowering geraniums normally grown as indoor and outdoor plants in Colorado are members of the genus Pelargonium. Common garden geraniums are subtropical in origin and are treated as annuals in Colorado because they do not overwinter outdoors.

Winter hardy outdoor geraniums which are members of the genus Geranium are usually called the hardy geraniums or cranesbills. These geraniums refer to approximately 300 species. Cranesbills are good additions to the perennial landscape border. Hardy geraniums are often grown as much for their decorative foliage as for their flowers. Leaves of hardy geraniums are typically divided into leaflets arranged in a palm-like fashion. Flowers have five equal-sized petals. They range in size from ¼ inch to 1-1/2 inches in diameter and can be violet, blue, pink, white and magenta. Hardy geraniums are incredibly tough and useful garden plants. They need little care, are pest- and disease-resistant and hardy to about -20 degrees F. Most are soft-stemmed herbaceous perennials that pass the winter season in dormancy and put on new leaves in spring. An explosion of new cranesbill varieties has hit the market over the past ten years.

Pelargonium geraniums range in height from a few inches to several feet, depending on the cultivar, age and maintenance of the plant. Many form types and species are available with great variation in leaf, flower and growth characteristics of geraniums.

Zonal Geraniums or Common Garden Geraniums usually have distinct zones or patterns in the center of the leaves. These plants are the ones most people recognize as “geraniums.” This category includes selections with tri-colored or silver leaves, leaves with bands or zones of red or white and deeply pleated or frilly foliage. Flower colors range from deep burgundy to red and pink to salmon and white. They may be single or doubly petaled.

Common or zonal geraniums are either seed-grown or cutting-grown. Geraniums from seed are mainly available in single-flowered forms only. Their flowers tend to shatter, which is an advantage because there is no need to pick off dead blooms.

Seed-grown cultivars include the following varieties:
• ‘Multibloom’ series is very early-flowering, with deeply zoned leaves on small plants. These produce up to 15 flower heads per plant at one time, virtually hiding the foliage, in vibrant colors of pinks, reds, lavender and white.
• ‘Cameo’ has round heads of deep coral salmon florets held well above the lightly zoned foliage.
• ‘Maverick’ series has full flower heads in a mixture of colors including pink, red, salmon, and coral.
• ‘Star’ is a vibrant pink and white bicolor. These have zoned foliage on multiple stemmed plants reaching up to 18 inches tall.

Most geraniums root easily from stem cuttings. Many cultivars must be propagated from stem to maintain flower and/or leaf color, shape, and scent. Cutting-grown cultivars include:

• ‘Lollipop’—orange
• ‘Gypsy’ and ‘Melody’—pink
• ‘Melody Red’ and ‘Sincerely Yours’—red
• ‘Lotus’ is white.
• ‘Mrs. Henry Cox’ is a striking zonal geranium with pink flowers that are upstaged by the dramatic yellow, deep red and green variegation of its leaves.

Ivy-leafed or Trailing geraniums have ornamental leaves that trail and resemble ivy foliage. The flower color range is similar to that of common garden geraniums. These geraniums are used in hanging baskets and window boxes.

Ivy geraniums should not be treated the same as common zonal geraniums. Ivy geraniums prefer moderate temperatures. When the temperatures are above 85 degrees F, hang the plant in a location that receives morning sun and afternoon shade. Ivy geraniums require moderate soil moisture levels with not too much and not too little moisture. Ivy-leafed geraniums include:

• ‘Summer Showers’ has a base branching habit that makes pinching unnecessary. This cultivar can be grown from seed.
• ‘Balcon’ geraniums bloom a bit later and have smaller flowers than common ivy geraniums, but they are much heavier-blooming and will trail two feet from a window box, even on the north side of a house. The flowers are ‘self-cleaning” and do not require deadheading.

Scented-leafed geraniums are prized for their foliar aromas. Scents include lemon, rose, peppermint, nutmeg and others. Oils are emitted when the leaves are rubbed or crushed. The leaves are used for potpourris, preserves, deserts, punches, vinegars, teas and sachets. Many have deeply lobed soft-textured leaves, often in shades of grey-green. Flowers are usually small and sparse. These geraniums are popular in herb gardens and along paths. Some common scented species include:

• Rose geranium (Pelargonium graveolens) has hairy deep green leaves that are divided and toothed, with a delicate spicy rose scent.
• Lemon geranium (P. crispum) grows to a height of two feet, with small stiff, curly leaves and lilac pink flowers. Fresh leaves give a pleasant lemon fragrance.
• Apple geranium (P. odoratissima) has trailing stems with small, soft, gray green leaves with a sweet apple scent and delicate white flowers.
• Peppermint geranium (P. tormentosum) has large heart-shaped wooly leaves with a strong mint scent.
• The “mosquito geraniums” are plants developed by introducing a gene form Citronella grass into a scented Pelargonium species. When rubbed or crushed, these geraniums release citronella oil which is supposed to repel mosquitoes. The validity of this claim has not been well documented.

Martha Washington geranium and regal geraniums are more often sold as indoor plants because they are not as heat tolerant as other geraniums and will not perform as well outdoors. These geraniums are noted for their large flowers, attractive foliage and extended flowering time. They are usually propagated from cuttings. Other names for this group include pansy, fancy or hothouse geraniums. High temperatures can inhibit flower bud formation on regal geraniums.

The authors have received training through Colorado State University Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  August 6, 2008