Zinnia Double Giant variety in glorious colors. Photo courtesy of the National Garden Bureau.
For decades, zinnias have been the flowering annual of choice for spreading glorious colors throughout the garden as well as for cutting to bring indoors. But it wasn't always so. When the Spanish first saw zinnia species in Mexico, they thought the flower was so unattractive they named it mal de ojos, or "sickness of the eye!" Years of breeding have brought striking new colors, shapes, sizes, and growing habits to the humble zinnia. No present day gardener would ever describe this versatile bloomer as anything less than eye catching.
The Zinnia Family Tree
There are more than a dozen species of zinnias, members of the Asteraceae (also known as Compositae) family, but very few of them are grown in home gardens. Zinnia elegans (syn. Z. violacea), the common zinnia, is very familiar to gardeners. Tall, mid-sized, and dwarf varieties of this species have been grown for decades, and flowers are available in a wide range of colors. Z. angustifolia (also known as Z. linearis) is less common in gardens, but is gaining in popularity. The plants have narrower foliage and smaller single flowers. The species has golden-orange flowers, but the variety, 'Crystal White', AAS (All America Selections) winner in 1997, offers pure white daisy-like blooms with yellow centers. It is more compact than the straight species, and may overwinter in Zones 9-11. Probably the least known of the garden zinnias is Z. haageana, or the Mexican zinnia. It is disease-resistant, grows to 15 inches, and has small, bicolored flowers.
A Bit of History—Then
When seeds of zinnias were collected and brought to Europe in the 18th century, the plants were not much to look at. Named for Dr. Johann Gottfried Zinn, who wrote the first description of the flower, the genus Zinnia had to wait for the mid-19th century to become successful in the garden. It is probable that the first “double” came from the West Indies, for it was from seed from those islands that double flowers were first introduced in France. Brightly colored 1 ½-inch ‘Lilliput’ type flowers were developed in France in the 1880s, and in the late 19th and early 20th centuries, separate colors of small, double flowers began to be grown. These were the precursors of what we now know as ‘Pumila’ or ‘Cut-and-come-again’ zinnias. ‘Giant Mammoth’, the first strain of large, double-flowered zinnias, appeared at around the turn of the century. But the start of the zinnia's real popularity began in the 1920s when Bodger Seeds Ltd. introduced the dahlia-flowered 'Giant Dahlia' zinnia. John Bodger discovered it as a natural mutation in a field of 'Mammoth' and within the next few years selected the large, flat-flowered 'California Giant' from the strain. Available in separate colors, it was considered to be a new trend in plant habit and flower form, and won a gold medal from the Royal Horticultural Society of England. ‘State Fair’, an example of a modern dahlia-flowered zinnia developed through induced tetraploidy, was introduced by the Ferry Morse Seed Company in 1939. Tetraploids have four, rather than the usual two sets of chromosomes; the plants have increased disease resistance, vigorous growth, and large flowers on strong stems. Only a few other zinnias available today are tetraploids.
Despite the breeding progress, the modern F1 hybrid was still waiting in the wings—or in the field, so to speak—because of the difficulty of emasculating (removing the male parts) a zinnia without destroying the flower itself. A chance find by breeder John Mondry, working at the time for W. Atlee Burpee, changed all that. He found a plant in the field with flowers that had no petals but were composed entirely of female reproductive parts. They could form seeds only after being cross-pollinated. The discovery led the way to the dwarf F1 hybrid 'Peter Pan' series introduced from 1971 to1980. Yoshiro Arimitsu and Charles Weddle bred seven separate colors that were recognized as AAS Winners. Bodger Seed Ltd introduced the F1 hybrid 'Ruffles' series ('Scarlet', AAS, 1974; 'Cherry' and 'Yellow', AAS, 1978), developed by Mondry (who had by then resigned from Burpee) as cutting flower plants. Although still available, these early hybrids have been largely supplanted in the market by later introductions.
Compact zinnias are now "in"--perhaps in response to home gardeners' smaller plots and the popularity of container gardening. Dwarf selections of Zinnia haageana were introduced decades ago, with 'Persian Carpet' and 'Old Mexico' garnering AAS awards in the 1950s and 1960s, and in 1997, 8- to15-inch Z. angustifolia 'Crystal White' was bred by Takii & Co, Ltd. Then a breeding breakthrough occurred. Two distinct species, Z. angustifolia and Z. elegans, were bred to create an interspecific cross. In 1999 the 'Profusion' zinnias, 'Cherry' and 'Orange', from Sakata Seed Corporation, won Gold Medals from AAS—the first in 10 years. They represented the best traits of both species: heat and humidity tolerance, disease resistance, easy maintenance (no deadheading required), pretty 2- to 3-inch single flowers, and compact growth (12 to 18 inches tall). These artificial interspecific hybrids developed at the University of Maryland have been given their own species name: marylandica. Subsequent hybrids of the kind are identified as Zinnia marylandica ‘Zahara Starlight Rose’, ‘Double Zahara Fire’, and ‘Double Zahara Cherry’, all 2010 AAS winners. With larger flowers than ‘Profusion’ and more color variations, they represent the new benchmark for beautiful, disease-resistant zinnias.
Zinnias—in All Their Glory
One of the reasons for the popularity of the zinnia is its diversity. Like dahlias and chrysanthemums, zinnias have a variety of flower forms—they may be single, semi-double, or double. Single-flowered zinnias have just one row of petals and the center of the flower is exposed: Z. angustifolia 'Crystal White' is a delightful example. Double-flowered zinnias, with so many rows of petals that the center is hidden, have several shapes. “Beehive” zinnias, with rows of flat petals on small blooms, such as 'Small World Cherry' (AAS, 1982), really do look like little beehives. Button-type flowers are similar to beehive except the flower is flatter. The edges of each petal on cactus-shaped flowers roll under and the petal twists and bends. Dahlia-flowered zinnias have large flat petals, and are usually semi-double, that is, the flowers have many rows of petals but the center can be seen; they are great to use as cut flowers.
Zinnias also come in an amazing array of colors. Most are solid, but some, in particular Z. haageana, are bicolored with a contrasting color at the tip of each petal. You'll find yellow, orange, cherry, pink, purple, scarlet, and white, as well as fashionable chartreuse—just about every color, in fact, but blue.
Height is an important consideration when planning a garden, and zinnias have growing habits to suit every need. Tall, 3- to 4-foot varieties are best for the middle or rear of a border or in a cutting garden. Dwarf plants grow 8 to 14 inches tall and do well in pots as well as at the front of a garden. Z. angustifolia plants are only about 12 inches tall and wide; they are excellent in the ground, in pots or hanging containers, and as summer-flowering ground covers.
Growing Zinnias From Seed
Zinnias are easy to start from seeds, indoors or outdoors. The seeds of most of them are a good size, so they're a perfect choice for a child to sow in the garden. For earlier flowers, and in colder zones, you may want to give the plants a head start by sowing the seeds indoors.
Starting seeds indoors:
Zinnias are fast growers, so plan to sow the seeds indoors about 4 to 6 weeks before the average last frost date in your area. In frost-free areas, count back from the date when you'll be planting tomatoes, impatiens, and other warm-weather annuals in the garden.
- Fill a shallow container (flat) or individual peat pots with a commercial seed-starting mix. Moisten the mix and let it drain.
- Sow the seeds in rows, so the seedlings will be easy to separate when it comes time to transplant them. If you're using peat pots, sow two to three seeds in each pot. Cover the seeds lightly with a layer of mix and spritz the mix with enough water to moisten it slightly.
- Cover the flat with a sheet of clear plastic wrap or place it in a plastic bag to keep the mix from drying out while the seeds are germinating. Set it in a bright location or under grow-lights. Keep the growing medium at about 75º - 80º F (24º - 26 ºC) by placing it on a heat mat or warm surface.
- Seedlings should emerge in about a week. Remove the plastic cover and keep the mix evenly moist—not soggy—by watering the flat from the bottom.
- When the seedlings have at least two sets of true leaves, transplant them into individual 2¼-inch or larger pots. Provide as much sunlight as possible so the plants don't get leggy from stretching for sun.
- Plant zinnias seedlings outdoors when the weather and soil have warmed up, about the time you plant impatiens or peppers.
- You can also sow the seeds directly in the garden, just as you would sunflowers and cosmos. Wait to sow until all danger of frost has passed and the air and soil are warm. Amend the soil by digging in a 2-inch layer of compost before planting for better drainage and improved fertility.
- It's easiest to sow the seeds in rows, but you can also sow them in groups. Cover smaller seeds (of Z. angustifolia, for instance) with about ¼ inch of soil, and larger seeds with ½ inch. Space seeds a little more closely than you'll want the plants to actually be as they grow; if you're sowing in groups, drop two or three seeds in each shallow hole. Keep the soil moist until the seeds germinate.
- When the seedlings have two pairs of leaves, thin them to the correct spacing. If you carefully pull out the unwanted seedlings, you can transplant them to other parts of the garden. Otherwise, simply snip them at ground level.
Buying Potted Plants
If you don't want to grow your plants from seeds, you'll find many zinnias at your local garden center or nursery. Growers and garden centers often sell zinnias in six-packs rather than in individual pots. Those plants will be smaller and may or may not be in bloom. When you buy, look for plants with healthy, green leaves, fairly compact growth, and good branching—it is actually better if they are not yet in bloom. If you can't plant the zinnias the day you bring them home, water them well and set them under a tree or patio cover where they'll be protected from the drying effect of direct sun.
Zinnias grow best in full sun, which means six or more hours of direct sun daily. In desert locales and cold-hardiness zones 9 to 11, choose a site that gets some shade at midday and in the late afternoon. They prefer a moist but well-draining soil—whether planted in the ground or in containers—so it’s important to prepare the planting bed by working in an organic material, such as compost, especially if the soil is sandy, or heavy clay.
The best time to transplant any plant is on a cloudy day or in late afternoon so that the tender young plants have a chance to get settled in before they have to contend with the drying effects of the sun. Don't crowd zinnias; air circulation is essential to keeping them disease-free. Set out plants so that taller zinnias (Z. elegans) are 12-18 inches apart; dwarf zinnias, 6-8 inches apart; and Z. angustifolia, 6-10 inches apart. Space the new 'Profusion' and ‘Zahara’ zinnias 12-18 inches apart. Plant zinnias in the ground at the same depth they were growing in the pots. If you're transplanting from flats or six-packs, try to keep as much soil around the roots as possible so they don't dry out. If you started the plants from seeds in peat pots, set the edges of the pots below the soil line—they have a tendency to wick moisture from the soil when exposed to the air. When growing zinnias for cutting, it’s a good idea to stake the plants unobtrusively when you set them in the ground, or shortly afterwards. Unsupported, the stems of taller zinnias will eventually flop over. Water the plants immediately after planting.
Caring for Zinnias
One of the nicest aspects of zinnias is that a part of their maintenance requirements, if you can call it that, is cutting the blooms frequently to keep the plants compact and bushy and producing more flowers. Otherwise, planted in the right site in good soil, they are fairly care-free. There are a few regular garden chores.
- Water regularly, if it doesn't rain. Even though zinnias love hot weather and came originally from arid regions, they do need moisture. Remember to check the soil in containers daily during hot summer weather and water if it is dry to a depth of 2 inches or more. In extremely hot, dry weather, you may need to water twice a day. Water at the bases of the plants, rather than sprinkling the foliage.
- Zinnias aren't heavy feeders, but fertilize plantings in the garden at least twice during the growing season. Use a balanced granular or water-soluble fertilizer—for instance, one with 20-20-20 on the label—or mix a slow-release or organic fertilizer into the soil when you plant. Always follow label directions for amounts.
- Mix a timed-release or organic fertilizer into the soilless mix when you plant zinnias in containers, or feed them once a month with water-soluble fertilizer or diluted fish emulsion. Be sure to dilute to the strength recommended on the label for containers.
Tops as Cut Flowers
There are few other garden flowers that are as wonderful as zinnias for cutting to use in arrangements—fresh or dried. With good reason, zinnias have been referred to for years as "cut and come again" flowers: Cut one flower stem above a pair of leaves and, within days, two new stems with flower buds will have taken its place. All Zinnia elegans varieties make excellent cut flowers. Use the taller kinds in large arrangements; the shorter, dwarf ones in miniature designs. Properly handled, zinnias will last at least a week in a vase before they begin to look "tired." Zinnia angustifolia is less frequently seen in designs, but the flowers are fairly long lasting and add a lovely airiness to arrangements.
To gather flowers for fresh arrangements, cut them early in the morning before the sun has had a chance to dry or wilt them. Select blooms that have not fully opened—they will continue to open indoors. Avoid tightly closed buds, which will not open once they're cut. Bring a bucket of water into the garden with you and place the stems in it as you cut so they don't become clogged by air bubbles. Once indoors, re-cut the stems under water, removing the lower leaves, and let the flowers "rest" for a few hours before arranging them.
To gather zinnias for use in dried arrangements, cut Z. elegans after the morning dew has evaporated. Dry the flowers in a desiccant, such as silica gel (available at garden centers and craft stores). The flowers will dry in about a week. Use large flowers in any arrangement, dwarf hybrids in miniature designs or, with four or five of the stems wired together to form a cluster, in larger arrangements.
Zinnias in Containers
Choose a window box, wooden half-barrel, rectangular or round pot, or hanging basket—the bigger the better. Because zinnias are available in so many colors and sizes, they lend themselves to striking displays, whether alone or in combination with other annuals. Low-growing zinnias are best for containers; Z. angustifolia and the smaller Z. elegans are excellent in hanging planters.
The container you select should have drainage holes in the bottom or sides. Fill it with a lightweight, soilless mix, rather than garden soil, which often contains disease pathogens and weed seeds, and will not drain well in a container. Arrange plants, in their nursery pots, on top of the soil until you have a pleasing design. Aim for a combination of taller plants in the center, medium and bushy plants around the middle, and a selection of trailing plants along the edge. Because zinnias, especially Zinnia elegans, can suffer without good air circulation, don't crowd the plants. When you're satisfied with the placement, remove the plants from their pots and set them in the mix at the same level they were growing originally.
Water the container well, and keep the soil evenly moist through the season. Plants, especially zinnias, in containers perform best if you fertilize them at least monthly with a water-soluble fertilizer, or save yourself the task and incorporate a controlled-release fertilizer in the mix before planting.
Pests and Diseases
Zinnias are often pest free for most of the growing season, but can be affected by two fungal diseases: powdery mildew and alternaria blight. Alternaria blight causes reddish brown spots on both foliage and flowers, and is a problem in the south more than any other area. Powdery mildew can cause Z. elegans varieties to look terrible by late summer or early fall, covering their leaves with a light gray mold. To camouflage the lower foliage of affected varieties of zinnias, plant them with shorter annuals in front.
The best offense against the fungal diseases is prevention: Don't wet the leaves and do space the plants so they have good air circulation. Z. angustifolia and Z. haageana are more mildew resistant than Z. elegans. Although newer plants, especially the interspecific crosses of Z. elegans and Z. angustifolia, such as 'Profusion' and ‘Zahara’, are very resistant to powdery mildew, preventive care is still warranted. With continued breeding efforts, gardeners may soon see disease-resistant tall zinnias among nursery and seed company offerings—which will give us yet another reason to celebrate this most adaptable and colorful of garden flowers.
The National Garden Bureau recognizes Eleanore Lewis as the original author of this fact sheet, and thanks Pam Ruch for her 2010 updates.
The National Garden Bureau recognizes the experts who read the first zinnia fact sheet and contributed their knowledge. They are: Howard Bodger, Bodger Seeds Ltd.; David Seitz, W. Atlee Burpee; Glen Goldsmith, Goldsmith Seeds and Dennis Kromer, Wild West Seed Inc.
The 'Year of the Zinnia' fact sheet is provided as a service from the National Garden Bureau. The use of this fact sheet is unrestricted.
To see fabulous photos of zinnia's visit the National Gardening Bureau's the Year of the Zinnia.