Geranium

Prepared by Karen Russ, HGIC Horticulture Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University (New 03/99. Images added 05/09.)

HGIC 1164

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Annual geraniums are popular for their wide range of brilliant flower color and attractive leaves. They can be grown as bedding plants and in containers on decks and patios, in hanging baskets, or in window boxes. They will grow in every part of South Carolina.

Red common garden geranium
Karen Russ, ©2008 HGIC, Clemson Extension

Height/Spread

There is great variation in leaf, flower and growth habit of geraniums. They vary in height from 6 inches to several feet, depending on the cultivar and the care given the plants.

Landscape Use

Geraniums need at least four hours a day of direct sunlight in order to flourish and flower well. In very hot areas it may be best to give the plants a few hours of shade midday.

Plant geraniums outdoors after all danger of frost is past and the soil has warmed.

Water abundantly after planting, and continue to water regularly, allowing the soil to dry out between watering. Never allow the plants to wilt or the leaves will turn yellow and drop off. Keep water off the foliage because moist foliage favors the development of disease. Mulch the bed to maintain moisture levels and keep the soil cooler in summer.

Soil for geraniums should be well-drained. Geraniums respond well to fertilizer and are stunted and yellowed if not provided enough nitrogen. Fertilize new flowerbeds with one pound of a 10-20-10 fertilizer or the equivalent per 100 square feet. Mix the fertilizer into the soil well. Geraniums usually require additional fertilizer during the growing season every four to six weeks. A water-soluble formula works well for follow-up fertilizations.

Take dead flowers off the plant to prolong flowering. Pinch to encourage well-branched, full plants.

When growing geraniums in containers, choose large pots to hold enough soil for a good root system, and to contain enough water to prevent wilting. Repot into larger containers if they grow so large that they wilt frequently. Select containers with adequate drainage holes, plant in a well-drained soil mix and do not allow pots to sit in water.

Problems

Bacterial leaf spot/blight causes spotting of the leaves, leaf drop and black rot of the stems. Botrytis blight is common during cool, moist weather. Oedema causes corky spots on the leaves and occurs when plants are over-watered. Reduce watering frequency, keep water off leaves, increase air circulation and make sure plants are in enough sun to reduce these problems. Keep plants cleaned of any dead, damaged, or yellowed leaves or flowers.

Aphids, caterpillars, mites and whiteflies may infest geraniums.

Species, Types & Cultivars

Common geraniums are actually members of the genus Pelargonium, while "true" geraniums include native wildflowers and herbaceous perennials. Major types of geraniums grown by home gardeners include the following:

Common Garden Geraniums or Zonal Geraniums: These geraniums often have distinct leaf markings. There are fancy-leafed selections with tri-colored leaves, silver leaves and leaves with white markings. Flower colors are usually pink, red, salmon or white.

A zonal geranium with white edged leaves
Karen Russ, ©2008 HGIC, Clemson Extension

Common and zonal geraniums are either seed-grown or cutting-grown. Geraniums from seed are mainly available in single-flowered form only. Their flowers tend to shatter, an advantage because you don't 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. They 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, coral and ' Star,' a vibrant pink and white bicolor. They have zoned foliage on multiple stemmed plants reaching up to 18 inches tall.

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

• 'Lollipop'is orange.
• 'Gypsy' and 'Melody'are pink.
• 'Melody Red' and 'Sincerely Yours' are red.
• 'Lucille'is coral.
• '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 Geraniums: These geraniums are trailing in habit with ivy-like leaves. They are used mainly in hanging baskets and window boxes.

Ivy-leafed geranium
Flickr: lilakb, Creative Commons license 2.0

Ivy geraniums are should not be treated the same as common zonal geraniums. Ivy geraniums prefer moderate temperatures. When the temperatures are above 85 °F, hang the plant in a location that receives morning sun and afternoon shade. Ivy geraniums require moderate soil moisture levels - not too much and not too little. One of the major problems seen on ivy geraniums is edema caused by fluctuating soil moisture.

• 'Summer Showers' has a base branching habit that makes pinching-out unnecessary. It 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: These geraniums are prized for their aromatic leaves. Most do not have showy flowers. Scents include lemon, rose, peppermint, nutmeg and others. The leaves are used for potpourris, preserves, desserts, punches, vinegars, teas and sachets. Some common scented species are:

• Rose geranium (Pelargonium graveolens) has hairy deep green leaves that are divided and toothed, with a delicate spicy rose scent.

Rose scented geranium in full bloom
Flickr: lilakb, Creative Commons license 2.0

• Lemon geranium (P. crispum) grows to a height of 2 feet, with small, stiff, curly leaves and lilac pink flowers. Its 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. tomentosum) has large heart-shaped wooly leaves with a strong mint scent.
• The "mosquito geranium" smells like citronella and is advertised as a natural mosquito repellant. This has not been proven.

Martha Washington Geranium & Regal Geraniums: These are sold during the winter as flowering pot plants. They are not heat-tolerant and will not perform as well outdoors as common geraniums.

If you want to overwinter your geraniums you can try these methods:

• Take cuttings in the fall and keep the plants on a bright, sunny windowsill during the winter.
• Dig large geraniums from the garden before the first frost and plant in large pots. Cut back and place in a sunny area such as a heated porch.
• Dig the plants before the first frost and hang the plants upside down in a cool, moist basement where they will not freeze. In spring, take the plants down, cut off two-thirds of the top growth and replant outdoors.

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