Geraniums are one of the most popular decorative plants for both indoor and outdoor use. There are two different groups of plants known as geraniums. The showy, flowering geraniums, normally grown as indoor and outdoor plants in Nebraska, are members of the genus 'Pelargonium.' They are subtropical in origin and are treated as annuals in Nebraska, since they do not overwinter outdoors.
Members of the genus 'Geranium,' which are winter hardy outdoor plants, are usually called the 'hardy geraniums' or cranebills. They are good additions to the perennial landscape border. Hardy geraniums are often grown as much for their decorative foliage as for their flowers. This NebGuide provides information about the Pelargonium geraniums.
Pelargonium geraniums range in height from a few inches to several feet, depending on the cultivar, age and maintenance of the plant. Many forms, types and species are available with great variation in leaf, flower and growth characteristics of geraniums.
Common Garden Geraniums or Zonal Geraniums usually have distinct leaf markings. 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, and they may be single or double petaled. They are usually sold as bedding plants.
Regal or Martha Washington Geraniums are more often sold as indoor plants because they usually are not as heat tolerant as other geraniums. They are noted for their large flowers, attractive foliage and extended flowering time and are usually propagated from cuttings. Other names for this group of geraniums include pansy, fancy or hothouse geraniums. High temperatures can inhibit flower bud formation on regal geraniums.
Ivy-leafed or Trailing Geraniums have ornamental leaves that trail and resemble ivy foliage. The flower color range is similar to that of the common garden geraniums. They are commonly used in hanging baskets and window boxes.
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. Many have deeply lobed, soft-textured leaves, often in shades of grey-green. The flowers are usually small and sparse. They are popular in herb gardens and along paths.
Mosquito Geraniums are plants developed by introducing a gene from Citronella grass into a scented Pelargonium species. When rubbed or crushed, these geraniums release the citronella oil, which is supposed to repel mosquitoes. The validity of this claim has not been well documented.