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!” What changes have been brought about over the years since–in flower colors and shapes, plant sizes, and disease resistance.
The Zinnia Family Tree
There are more than a dozen species of zinnias, members of the Compositae, or daisy family, but only three species are regularly grown in home gardens. All three are annuals and bloom from early summer through the first frosts in autumn—longer in areas that are frost-free. Zinnia elegans, known as common zinnia, is very familiar to gardeners; varieties -tall, medium and dwarf–have been part of gardens for decades. Flowers are available in just about every color except blue. Z. angustifolia (also known as Z. linearis) may be 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’ (All-America Selections winner in 1997) offers pure white blooms with yellow centers. ‘Crystal White’ is also more compact than the species, which can spread to 2 feet. Z. angustifolia may overwinter in Zones 9-11. Probably the least known of zinnias is Z. haageana, or the Mexican zinnia. It is disease-resistant, grows to 15 inches, and has small, bicolored flowers; it’s an excellent cut flower because of its long stems.
A Bit of History–Then
Even after seeds of zinnias were sent back 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 late 19th century to become more successful as a garden annual. Breeding by selection occurred in Germany, Holland, and Italy: ‘Pumila Mixed’ (precursors of the “cut-and-come-again” zinnias) and two selections from that strain, ‘Mammoth’ and ‘Striata’, were brought to this country and enjoyed great success with gardeners. But the start of the zinnia’s real popularity began around 1920 when Bodger Seeds Ltd. introduced the dahlia-flowered ‘Giant Dahlia’. 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. It was available in separate colors and was considered to be a new trend in plant habit and flower form. It won a gold medal from the Royal Horticultural Society of England. The first tetraploid zinnia, called ‘State Fair’, came from Ferry Morse Seed Company in the 1950’s. (Tetraploids have four, rather than the usual two, sets of chromosomes; they are plants with larger flowers on stronger stems, vigorous growth, and increased disease resistance.) Dwarf selections of Zinnia haageana were introduced: ‘Persian Carpet’ (All-America Selections award, 1952) and ‘Old Mexico’ (AAS, 1962). F1 hybrids waited 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. That 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, now sold by Goldsmith Seeds, a wholesale seed company. Bodger Seed Ltd introduced the F1 Hybrid ‘Ruffles’ series (‘Scarlet’, AAS 1974; ‘Cherry’ and ‘Yellow’, AAS, 1978), developed by Mondry (who had resigned from Burpee) as cutting flower plants.
And Now–Breakthrough Zinnias
Compact zinnias are “in”–perhaps in response to home gardeners’ smaller plots and the popularity of container gardening. In 1997, ‘Crystal White’, Z. angustifolia bred by Takii & Co, Ltd won an award from AAS; it’s more compact than the species and offers a new color. In 1999 the ‘Profusion’ zinnias, ‘Cherry’ and ‘Orange’, from Sakata Seed Corporation won Gold Medals from AAS–the first in 10 years. They represent a breakthrough in breeding for zinnias. They are interspecific crosses; that is, the result of crossing two species, Z. angustifolia and Z. elegans. They represent the best of both: heat and humidity tolerance, disease resistance, easy maintenance (no deadheading of spent blooms required), pretty 2- to 3-inch single flowers, and compact growth (12 to 18 inches tall). They will be the benchmark for future zinnias, and they open up incredible possibilities for this garden favorite.
Zinnias–in All Their Glory
One of the reasons for the popularity of the zinnia is the diversity of its forms. Like dahlias and chrysanthemums, zinnias have a variety of flower forms and may be single, semidouble, 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. There’s beehive, small blooms with rows of flat petals, such as ‘Small World Cherry’ (AAS, 1982), which 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. The petals on dahlia-flowered zinnias are large and flat and usually semi-double, which means that the flowers have many rows of petals but the center can be seen; they are great to use as cut flowers.
Zinnias also have an amazing number of colors; in fact, flowers come in almost every shade except blue. 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 one unique chartreuse variety called ‘Envy’.
Heights are an important consideration when planning a garden, and zinnias have growth habits to suit every need. The 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 reach only 8 to 15 inches in height with an equal spread; 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, too, so they’re a perfect choice for a child to sow in the garden as well. 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 three to four seeds in each pot. Cover the seeds lightly with a layer of mix and spritz the mix with enough water to moisten it slightly.
Enclose the flat in a sheet of clear plastic wrap or in a plastic bag closed with a twist tie to keep the mix from drying out while the seeds are germinating.
Set the flat in a warm, bright location or under grow-lights. Keep the growing medium at about 75º – 80º F (24º – 26 ºC)
Seedlings should emerge in 6 to 10 days. Remove the plastic cover and keep the mix evenly moist—not soggy—by watering the flat from the bottom to prevent water getting on the foliage.
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 young plants don’t get leggy from stretching for sun.
Plant zinnias outdoors when the weather and soil have warmed up, about the time you plant impatiens or peppers. Sowing seeds directly in the garden. Along with some other annuals such as marigolds, zinnias do very well if you sow them outdoors right where you want them to grow. Wait to sow until all danger of frost has passed and the air and soil are warm.
Prepare the soil (see below). It’s easiest to sow the seeds in rows, but you can sow them in groups if you want. Sow smaller seeds (of Z. angustifolia, for instance) about ¼ inch deep and larger seeds ½ inch deep. Place seeds a little more closely spaced 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.
Cover the seeds with soil and water well. 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 off the seedlings 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. The plants may be labeled with names or with colors only. Growers and garden centers also often sell zinnias in six-packs rather than in individual pots. Those plants will be smaller and may or may not be in bloom, but they should be in bud. It’s actually better to buy plants in packs “green,” those that aren’t in bloom. When you buy plants, look for healthy, green leaves with no discoloration above or underneath. Select plants with fairly compact growth and good branching. 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.
Planting Zinnias
Selecting a site. Zinnias grow best in full sun, which means six or more hours of direct sun daily. In desert locales and Zones 9 to 11, choose a site that gets some shade at midday and in the late afternoon. They prefer a soil that drains well—whether they’re planted in the ground or in containers—but other than that requirement, they will grow in just about any soil, whether it’s clayey, sandy, or the ideal loam. Preparing the soil. When you have selected a site, amend the soil by digging in a 2-inch (5 cm) layer of compost or peat moss before planting to ensure good drainage and fertility.
Transplanting into the garden. The best time to transplant any plant is on a cloudy day or in late afternoon so that the plants have a chance to get settled in before they have to contend with the drying effects of the sun. Set 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 pots below the soil line because the pots have a tendency to dry out quickly when exposed to the air. Don’t crowd zinnias because air circulation is most important to keep them disease-free. Space taller zinnias (Z. elegans) 12-18 inches apart; dwarf zinnias, 6-8 inches apart; and Z. angustifolia, 6-10 inches apart. Space the new ‘Profusion’ zinnias 12-18 inches apart. If you’re growing zinnias for cutting, stake or cage the plants when you set them in the ground. Unsupported, the stems of taller zinnias won’t grow straight or may flop over. Water the plants immediately after planting.
Caring for Zinnias Through the Season
One of the nicest aspects of zinnias is that part of their maintenance requirements, if you can call it that, is to cut 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’s dry to a depth of 2 inches or more. In really hot, dry weather, you may need to water twice a day. When you water, try not to get moisture on the foliage. Although newer hybrids are mildew resistant, they are not totally free of the disease.
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, use a slow-release fertilizer when you plant; follow label directions for amounts. Zinnias will bloom into fall, so you may want to give them a boost of fertilizer in late summer.
Mix a timed-release fertilizer into the soilless mix when you plant zinnias in containers or feed them once a month with water soluable fertilizer diluted 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 make good 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 often add 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 haven’t fully opened–they will continue to open indoors. Buds that have started to open are also good, but tightly closed buds won’t 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 the stems don’t become clogged by air bubbles. Once indoors, recut the stems under water, removing any leaves that would be under water, and then 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 dessicant, 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 into a cluster, in larger arrangements.
Zinnias in Containers
Whatever kind of container you choose–windowbox, wooden half-barrel, rectangular or round pot, or hanging basket–you’ll be really pleased with the effect that zinnias create. Because they 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.
Planting in containers. Select a container that has drainage holes in the bottom or sides. Fill the container with a lightweight, soilless mix, not soil from the garden because it may not have good drainage and may carry diseases or weed seeds. Garden soil is also heavier–a consideration if you want to move the pot.
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 like good air circulation, don’t set plants closer together than you would in the ground. When you’re satisfied with the placement, unpot the plants and set them in the mix at the same level they were growing originally.
Water the container well after planting 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 basically pest free. For years, though, they have been known to be affected by two fungal diseases: powdery mildew and alternaria blight. Alternaria blight causes reddish brown spots on both foliage and flowers; it is a problem in the south more than any other area. Until recently, powdery mildew (a fungal disease) caused many zinnias to look really awful by late summer or early fall, covering the leaves with a light gray mold. To camouflage the affected foliage of older varieties of zinnias, plant them with shorter annuals in front.
The best offense against the fungus was and is prevention: Don’t get the leaves wet and do space the plants so they have good air circulation. Z. angustifolia and Z. haageana are more mildew resistant than most Z. elegans. Newer plants, especially the interspecific crosses of Z. elegans and Z. angustifolia, such as ‘Profusion’, are very resistant to powdery mildew.
The National Garden Bureau recognizes Eleanor Lewis as the author of this fact sheet. Four experts reviewed the text before publishing. We wish to thank them for their comments. They are Howard Bodger, Bodger Seeds Ltd.; David Seitz, W. Atlee Burpee; Glenn Goldsmith, Goldsmith Seeds and Dennis Kromer, Wild West Seed Inc. The photography was taken by Liz Ball, Garden Portraits or Tom Eltzroth. The logo drawing was created by Nola Nielsen. The fact sheet was designed by Johanna McCormick.
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