Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/19/99
Contacts:
Richard Jauron, Reiman Gardens, (515) 294-1871
Elaine Edwards, Extension Communication Systems, (515)
294-5168
Yard and Garden Column for the Week Beginning April 23
Marigolds -- Reliable Garden Performers
by Richard Jauron
Extension horticulturist
Iowa State University
A native of Mexico, marigolds have been grown in gardens throughout the world for hundreds of years. Today, they are one of the most popular bedding plants in the United States. Marigolds are easy to grow, bloom reliably all summer and have few insect and disease problems. The marigold's only shortcoming is its pungent aroma.
There are numerous marigold varieties available to home gardeners. Many of the commonly grown marigolds are varieties of African and French marigolds. Less known are the triploid hybrids and the signet marigolds.
The African marigolds (Tagetes erecta) have large, double, yellow-to-orange flowers from midsummer to frost. Flowers may measure up to 5 inches across. Plant height varies from 10 to 36 inches. African marigolds are excellent bedding plants. Tall varieties can be used as background plantings. Suggested African marigolds for Iowa include varieties in the Inca and Perfection series. A series is a group of closely related varieties with uniform characteristics, such as height, spread and flowering habit. The only characteristic that varies within a series is flower color. African marigolds also are referred to as American marigolds.
The French marigolds (Tagetes patula) are smaller, bushier plants with flowers up to 2 inches across. Flower colors are yellow, orange and mahogany-red. Many varieties have bicolored flowers. Flower heads may be single or double. Plant height ranges from 6 to 18 inches. The French marigolds have a longer blooming season than the African marigolds. They generally bloom from spring until frost. The French marigolds also hold up better in rainy weather. French marigolds are ideal for edging flower beds and in mass plantings. They also do well in containers and window boxes. Queen Sophia, Troubadour Yellow and Golden Gate are excellent French marigold varieties. Varieties in the Boy, Bonanza, Hero, Janie and Safari series also perform well in Iowa.
The triploid hybrids are crosses between the tall, vigorous African marigolds and the compact, free-flowering French marigolds. Triploid hybrid marigolds are unable to set seed. As a result, plants bloom repeatedly through the summer, even in hot weather. One problem with the triploids is their low seed germination rate. Average germination is around 50 percent. Since the triploid hybrids are unable to produce viable seed, they also are known as mule marigolds.
Signet marigolds (Tagetes tenuifolia) are quite different from most marigolds. Signet marigold plants are bushy with fine, lacy foliage. The small, single flowers literally cover the plants in summer. Flower colors range from yellow to orange. They also are edible. The flowers of signet marigolds have a spicy tarragon flavor. The foliage has a pleasant lemon fragrance. Signet marigolds are excellent plants for edging beds and in window boxes. The varieties Lemon Gem, Golden Gem and Tangerine Gem do well in Iowa.
There are basically three marigold planting options available to home gardeners. Marigold plants can be purchased at greenhouses and garden centers. Other options are to sow marigold seed outdoors when the danger of frost is past or to start them indoors 6 weeks prior to the last frost date.
Planting site requirements for marigolds are full sun and a well-drained soil. Plant spacing varies from 6 to 9 inches for the French marigolds and up to 18 inches for the taller African marigold varieties.
Summer care of marigolds is simple. Water occasionally during dry weather and pinch off faded flowers to encourage additional bloom. Tall African marigolds may require staking to prevent the plants from falling over or lodging during storms.
While marigolds are seldom bothered by insects and diseases, they are not problem free. Spider mites can devastate marigolds in hot, dry weather. Grasshoppers also can cause considerable damage. Aster yellows is occasionally a disease problem. Aster yellows is caused by microorganisms called phytoplasmas. The disease is transmitted from plant to plant by sap-sucking insects such as leafhoppers. Marigolds infected with aster yellows are stunted, yellow-green in color and their flower buds fail to open. Infected plants should be removed and destroyed.
In a related matter, some gardeners plant marigolds in their vegetable gardens to repel harmful insects. While the marigolds are an attractive addition to the garden, research studies have concluded they aren't effective in reducing insect damage on vegetable crops.
ml: isugarden
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