Geranium Culture

• Indoor Care
• Outdoor Care
• Propagation
• Additional Information
• Diseases
• Fungicides

Common Garden Geraniums -- usually characterized by distinct leaf markings. They include selections with tri-colored leaves, silver leaves, leaves with white markings, and fancy-leafed geraniums. Flower colors are usually pink, red and/or white.

Ivy-leafed Geraniums -- are trailing in habit and have leaves that resemble ivy leaves. They are commonly used in hanging baskets and window boxes.

Scented-leafed Geraniums -- are prized for foliar aromas. Scents include lemon, rose, peppermint, nutmeg and others. Many have deeply lobed leaves.

Indoor Care

Fertilize monthly from March through October and bi-monthly the rest of the year. Use one tablespoon of 20-20-20 fertilizer, or two tablespoons of a 10-10-10 fertilizer per gallon of water. If light intensity is low, reduce the fertilizer accordingly.

Grow geraniums in a soil medium that is high in organic material. A good soil mix consists of equal parts garden loam, peat moss and coarse sand or perlite. Other mixes can work equally well. Commercial soil mixes also may be satisfactory.

Allow the soil to become moderately dry between waterings, and make sure there is one or more bottom holes in each container. Good drainage is essential.

Outdoor Care

The soil should be well drained with adequate organic matter. Fertilize new flower beds with one pound of a 10-20-10 fertilizer, 2 pounds 6-10-4, or comparable amounts of similar fertilizer per 100 square feet. Incorporate the fertilizer into the soil. If fertilizer is applied after planting, make sure the soil is moist.

Water geraniums when the soil becomes moderately dry. Never allow the plants to wilt or the leaves will turn yellow and drop off. Give the soil a good soaking at each watering, and avoid frequent light waterings. Keep water off the foliage because moist foliage favors the development of disease. Mulching usually is desirable for most summer flowers, including geraniums.

Removing dried or faded flowers from the geranium plants promotes more blooming, and makes the plants more attractive. Pinch tall plants occasionally to encourage well branched, stocky plants.

Geranium plants can be overwintered in several ways. Before frost, whole plants can be taken from the garden, tied in bundles, and hung by root ends in a cool basement or moist area for the winter. Storage temperature should be between 35 and 45° F, and the humidity should be 80 percent or higher. The plants can be cut back to about 1/3 of their height and planted outdoors in May, or potted indoors in late winter.

Plants also can be dug in the fall, taking as much of the root system as possible. Place the plant in a pot large enough to accommodate the root system, cut back to 6 inches in height, place in a sunny window and water and fertilize as needed. Geraniums also can be overwintered from cuttings taken in late summer or early fall.

Propagation

Cuttings:

Cut off shoot tips 4 to 6 inches in length, remove the leaves on the lower part of the stem, and place in a rooting medium.

Satisfactory rooting media include coarse sand, perlite, vermiculite or a mixture of these. Mixtures such as 1/2 sand + 1/2 perlite, 1/2 perlite + 1/2 peat moss, or 1/2 sand + 1/2 peat moss work very well.

The use of a rooting hormone is recommended to stimulate the rooting process. This product is available at most garden centers. Dip the bottom 1/2 inch into the hormone powder and shake off the excess powder before placing the cuttings in the rooting medium.

Select a container 3 to 4 inches deep for rooting the cuttings. Fill the container with the moist medium (not overly wet), then insert the cuttings to a depth of 1 1/4 to 1 1/2 inches. Firm the medium around the cuttings.

Avoid crowding the cuttings so there will be some air movement to help prevent disease.

Cover the container with a plastic bag. This helps prevent excessive moisture loss, decreases wilting and increases rooting.

Place the container in a warm location that receives bright, but indirect sun. Avoid excessive heat buildup within the bag.

Check the rooting medium for moisture every week. It usually stays fairly moist for several weeks before additional water is needed.

Plant the cuttings into small individual containers filled with a coarse, well-drained soil mix, when new roots are 1/2 to 1 inch long. Pot at the same depth as the cuttings were placed in the rooting medium. Gradually move the plants into more direct light.

Seed:

Cover the seeds with 1/8 inch of media. Keep the media moist, but not saturated, and maintain the media temperature between 72 and 77° F. Seeds normally germinate in 10 days to two weeks.

When the seedlings are 1/2 inch to 1 inch tall, transplant them to individual containers. Maintain the seedlings under high light intensities with temperatures of 60 to 70° F during the day and slightly cooler night temperatures until the weather is favorable for outdoor planting.

Additional Information

Diseases

Strict sanitation is basic to the successful culture of disease-free geraniums. If necessary, fungicides can be used to augment sanitary measures, but they cannot replace them. Commercial growers should familiarize themselves with common diseases and be prepared to act promptly if serious disease problems arise.

Rotating the geranium bed, so that at least three years elapse before the site is again planted to geraniums, is probably the most practical preventive disease control measure available to the home gardener. Fungicide treatments are costly (although usually effective) and the value of the bed may not justify their use. This is a decision gardeners have to make for themselves.

Table I. Diseases of Geraniums

Disease	Symptoms	Conditions that favor disease	Control
Botrytis Blight Botrytis cinerea	Blossom blight: premature fading and drying of petals; petals turn dark at margins, then wilt. Leaf spot: irregular, brown, water-soaked spots at leaf margins; spots often covered with gray-brown mold-like growth. Stem rot: light to dark brown rot of stem cuttings.	Primarily a greenhouse problem where relative humidity is high and air circulation poor.	Remove and destroy infected foliage; ventilate greenhouse to lower relative humidity; space plants sufficiently to allow air circulation around individual plants; avoid splashing water onto foliage; apply a foliar fungicide for persistent problems; sterilize cutting benches.
Rust Puccinia pelargonii- zonalis	Small yellow spots up to 1/4 inch in diameter form on underside of leaves; rust-colored pustules develop within the spots on lower leaf surface; later small pustules form as a circular zone around the first pustule; leaves yellow and drop prematurely.	Moderate temperatures and 6 to 8 hours free moisture on foliage; occurs on both garden and greenhouse geraniums; rust spores spread by wind and air currents in greenhouse.	Avoid splashing water on foliage; remove and destroy infected foliage; isolate imported plants; apply a fungicide every 10 days as a preventative; dip cuttings into fungicide solution.
Alternaria Leaf Spot Alternaria tenius	Small brown spots with alternating light and dark bands; most evident on lower surface of older leaves.	Occurs on garden geraniums during cool, wet weather; fungus rarely sporulates on attached leaves but does so readily on fallen leaves.	Remove and destroy infected foliage; apply foliar fungicide at first appearance of disease.
Bacterial Blight Xanthomonas campestris pv. pelargoni	Leaf symptoms: small, sunken, water-soaked spots on under-surface of leaves; rapid necrosis and wilting of affected leaves; infected areas turn brown to black; leaves may wilt at margins followed by angular necrosis; limp condition of leaf associated with bacterial blight; affected leaves may droop or fall from the plant. Vascular wilt symptoms: infected stems turn dark brown to black and leaves on affected branch wilt; stems shrivel into a dry rot; infected cuttings rot from base upward.	Symptoms most prominent at temperatures of 70 to 80° F; bacteria spread through cuttings, contaminated tools, cutting benches, soil, plant-to-plant contact and white flies.	Strict sanitary measures when establishing cuttings; careful watering; space plants sufficiently; control insects; maintain balanced fertility; rotate beds.
Verticillium wilt Verticillium albo-atrum	Upper and middle leaves of infected plants yellow and drop prematurely; older leaves unaffected; plants suddenly wilt and die.	Pathogen spread by contaminated soil and cuttings.	Destroy infected plants; take only tip cuttings; grow varieties known to be resistant, rotate beds.
Blackleg Pythium spp.	Brown water-soaked discoloration on roots near base of cuttings; base of stem turns a shiny black; blackening of petioles; affected cuttings and seedlings wilt and die rapidly.	A disease of cuttings and young greenhouse plants; spread by contaminated cutting benches and tools and potting soil mix.	Sterilize cutting medium, potting mix, cutting bench tools, etc.; soil drench with fungicides at planting.
Tomato Spotted Wilt Virus (TSWV)	Symptoms range from stunting to ringspots to dark purple-brown sunken spots to stem browning and death to flower breaking. In geraniums it is characterized by bright-yellow or white spots or rings.	TSWV is transmitted by thrips. Greenhouse conditions that favor thrips will favor spread of the virus.	The first step is to get rid of all infected plants and the second step is to control thrips with insecticides. Once TSWV is detected in a greenhouse, an intensive management program to control thrips should be initiated.
Other Virus Diseases Crinkle Leaf or Leaf Curl Leaf Breaking (Mosaic) Leaf Cupping	Crinkle Leaf: yellow spots with small necrotic areas; brown, elongated, corky areas on stems and petioles. Leaf Breaking: yellowing between veins with purple spotting along the veins. Leaf Cupping: leaves cup inward and become hairless cups with sinuous veins and cleared veinlets.	Crinkle leaf disease is severe during spring; leaf breaking disease occurs during winter.	Rogue diseased plants; take cuttings from virus-free plants.
Nematodes	Plants appear off-colored and stunted with marginal browning of leaves; galls on roots; stubby roots; excessive root branching.	Plant parasitic nematodes survive in soil; spread by soil particles clinging to garden tools and movement of water in the soil.	Sanitation measures such as cleaning tools, sterilization of potting mixes, etc.
Odema Nonparasitic Disease	Rupturing of tissue on leaves produces raised water-soaked spots that become corky.	Odema is likely to occur when the soil is moist and warm and the air is moist and cool; symptoms most predominant during late winter and early spring.	Remove affected leaves; avoid over-watering.

Table II. Fungicides for Control of Geranium Diseases

Fungicidea	Diseases	Clienteleb
Benlate, 50 WP	Botrytis Blight	C, H
	Drench and Preplant Treatment for Botrytis, Fusarium and Rhizoctonia	C, H
Bordeaux Mixture, 12.75 WP	Leaf Spots	C, H
Botran 75 W, 75 WP	Botrytis Blight	C
Daconil 2787, 6F, 75 WP	Botrytis Blight	C, H
Dexon, 35 WP	Drench Treatment for Damping Off (Pythium and Phytophthora)	C
Maneb, 80 WP	Botrytis Blight	C, H
Terrachlor, 75 WP, 10 G	Soil Treatment for Control of Rhizoctonia	C

No criticism is intended for fungicides not listed.

"C" represents commercial grower; "H" represents home gardeners.

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