The Lazy Gardener’s Guide To Direct Sowing Zinnias
Direct sowing zinnia seeds is one of the easiest ways to ensure vibrant rounds of color in the summer landscape. The reliable annuals become fast favorites for beginners and tried-and-true staples for experienced gardeners. Gardening expert Katherine Rowe reviews the lax way to direct sow zinnias for high returns.
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Zinnias bring sweeping annual color with vibrant ray-petaled blooms. Their flowers in single and double forms range from pink to carmine to lime. Waving on tall stems or blanketing low, mounding foliage, various heights make them versatile across garden spaces.
Zinnias are one of the easiest plants to grow. They’re at home in the ornamental border, the vegetable bed, the cottage garden, and the wildflower arrangement. Heat-loving, they bloom all summer until frost. With open petals and accessible nectar and pollen centers, the colorful rays with disk florets are pollinator magnets.
Adding to their merits, the annuals grow quickly from seed. By direct sowing zinnias this spring and summer, we can enjoy their blooms in short order.
Growing Zinnia From Seed
Zinnias are workhorse annuals for their low maintenance, rapid development, and profusion of blooms, whether on singular stalks or covering a bushy form. Their easy seeding adds to the appeal, and direct sowing is one of the best ways to grow zinnias.
Direct sowing exposes seeds to the natural conditions they require to germinate. It eliminates the need for seed-starting supplies and indoor growing space. It also preserves the young roots, which are sensitive to transplant disturbance. Direct sowing zinnias in the right site gives them a strong foundation.
For fresh blooms all season, consider succession planting. Sow another round of zinnia seeds every two to three weeks until early summer for a nonstop bloom show. Younger plants take the place of those that may slow from all their production in the summer heat. Sow up until about three months before fall’s first anticipated frost date to give enough time for flowering. A late round of direct sowing zinnias produces early fall color.
To get the most value for pollinators, make sure your variety is a nectar and pollen producer. Some cultivars lose these traits in breeding, or their fully double petals may make accessing the yellow center a challenge. Classic zinnias (Zinnia elegans), ‘Cut and Come Again,’ ‘State Fair,’ ‘California Giants,’ and ‘Benary’s Giant,’ among many others, attract and support pollinators.
Prep the Site
Zinnias are native to Mexico and Central America and thrive in the heat and full sun. They need at least six hours but appreciate eight or more. Well-drained soils are essential. Partnered with sun exposure, good drainage prevents pests and fungal diseases, especially in humid climates.
Loose, organically rich soils set the stage for showy blooms, though zinnias tolerate various types. Compacted soils or heavy clays that hold water are a challenge. Amend poor soils with compost to boost aeration and drainage capacity.
To reduce competition, pluck any weeds before planting. Zinnia seeds work well around existing specimens or with mixing with other seeds at sowing, as long as they have room for mature growth. The easy blooms have a rugged constitution, though they are prone to powdery mildew. Choose resistant varieties in humid climates, and ensure proper spacing and balanced watering to stave off fungal issues.
When to Plant
Wait until the soil warms to direct sow zinnias. The cold-sensitive annual won’t show strong germination until conditions are warm enough. Sow them after the final frost and when soils warm to 70°F (21°C) or more. You can also start indoors four to six weeks before transplanting them in 60°F (16°C) or warmer soils. But with unfussy zinnias, scattering a bunch of seeds for quick development couldn’t be easier.
Optimal air temperatures for germination and seedling development are 70 to 75°F (21-24°C) during the day and 65 to 70°F (18-21°C) at night.
How to Direct Sow
With a clean, prepped site, scatter seeds on the smooth soil surface. Cover them lightly with ¼ inch of soil, either with a rake or a light brush of the hand. The seeds need darkness to germinate, and thin coverage allows exposure to warmth and moisture.
Slightly less lazy is to press one or two seeds lightly to a ¼ inch depth. Doing each by hand allows more control over the spacing, uses fewer seeds, and means less thinning.
Spacing varies by variety, but usually falls between 8 inches and two feet. Tall, singular stems grow close together, while those with a spreading, mounding habit need more room. Check the spacing guidelines on the seed packet to sow them accordingly, or sow extra and plant to thin to the proper spacing for mature growth and air circulation.
Thinning and Tending
As sprouts emerge, thin them to the proper spacing. Thinning reduces competition for moisture, nutrients, and sunlight, and promotes that all-important air circulation for zinnias. Thin seedlings by clipping them at the base. Clipping, rather than pulling, avoids disturbing the roots of the remaining stems.
For long-stemmed zinnias, pinching when they’re young generates more branching and more blooms. When seedlings reach 6 to 8 inches tall with three to four sets of leaves, clip three to four inches off the main stem, just above a leaf node. The growth point will send off multiple branches and longer stems to hold their flowers.
Irrigate and Fertilize
Sprouting seeds require regular water, and with warm temperatures, that’s usually daily. Zinnias prefer even moisture, especially as young seedlings and transplants with small root systems. Keep the soil moist for a few weeks after sowing. Once established, the adaptable annuals tolerate short periods of drought and can dry out between waterings. If the soil is dry to the depth of an inch or two, it’s time to water.
Well-draining soils are essential. Overwatering and soggy situations lead to fungal problems, so err on the dry side for zinnias. They’re susceptible to powdery mildew in damp conditions with low air flow. If feasible, water at the base to avoid wetting the leaves. Provide ample spacing to maintain good air circulation.
Since zinnias do all their growing and flowering in a single season, they benefit from a boost in nutrients and minerals to flourish. Start with a foundation of organically rich soil. Apply an organic balanced fertilizer like 8-8-8 or 10-10-10 at planting. A slow-release granular lasts for a couple of months and distributes nutrition over time.
To promote more blooms, switch to a fertilizer higher in phosphorus after the initial spread at planting. A monthly liquid feed tailored to flowering species keeps the flowers coming. Or, opt for a granular for less frequent application.
Trimming and Deadheading
While not essential, zinnias respond well to deadheading to promote more blooms. This directs energy into producing more flowers rather than seed production. Harvest them freely to use in fresh florals to yield more flowers.
Pinch any thin stems that can’t support the large blooms. Clipping weak stems sends energy toward new growth and flowering.
Collecting Seeds
Another beauty of zinnias is that they may naturally reseed in the landscape. Stop deadheading or harvesting blooms in late summer so they can set seed. The seeds left for the birds or to disperse in the place are the start of next year’s crop.
The easiest way is a hands-off approach, letting nature take its course with the blooms that remain. You can move things along by tipping the stem to the ground level. Or, pick the dried bloom and crush it to release and scatter the seeds. Walk over the area to tamp or lightly rake it to promote seed-to-soil contact.
Collecting zinnia seeds to store and sow in spring is easy and rewarding. Once flowers dry on the stem, pick them and remove the ray petals. Little achenes (fruits that hold one seed) will burst from the central disk. Store these in a cool, dry, dark area for direct sowing in spring. Keep in mind that if you’re growing more than one variety of zinnia or a hybrid, they won’t come true to type from seed. Because zinnias are open-pollinated by insects and the wind, their genetics cross in the process, and your new seedling may look different than its parent.
Popular Varieties
In a rainbow of colors and a multitude of floral structures, there’s a zinnia for every sunny garden. Direct sowing zinnias allows us to curate our collection and choose seeds we may not find as nursery starts. It also lets us grow our favorite varieties in numbers without a big investment.
Mexican
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botanical name Zinnia angustifolia |
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sun requirements Full sun to partial shade |
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height 6-18” |
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hardiness zones 2-11 |
Mexican zinnia is a fit for the border with a blanket of gold blooms until frost. The bright ray petals have deep orange central discs with varieties in red, orange, purple, and tricolor, with single, double, or semi-double one-inch flowers.
Mexican zinnia is disease-resistant and thrives in high heat and humidity. They have a long bloom season, attract pollinators, and are deer-resistant. The tough annual is a Fleuroselect winner and a Dallas Arboretum “Flameproof” selection for its performance in heat-tolerant trialing.
Hardy hybrids of Z. angustifolia like ‘Profusion Orange’ (a Royal Horticultural Society Award of Garden Merit recipient) boast drought tolerance and disease resistance. ‘Profusion’ performs across climates with pincushion blooms from summer through fall.
The single or double blooms are smaller than traditional zinnias on forms that softly mound instead of standing tall. ‘Orange,’ ‘White,’ ‘Cherry,’ and ‘Double Deep Salmon’ are All-America Selections award winners. ‘Cherry’ is a Fleuroselect Gold Medal recipient.
‘State Fair Mix’
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botanical name Zinnia elegans ‘State Fair Mix’ |
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sun requirements Full sun |
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height 30-40” |
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hardiness zones 2-11 |
‘State Fair Mix’ is a carnival of color with jumbo, five-inch blooms in red, purple, pink, orange, yellow, and bicolors. The heirloom has “award winner” in its breeding, with vigorous growth and high yields. Tall, strong, upright stems hold single blooms on a mounded form.
‘State Fair Mix’ performs well in high heat with good disease resistance. The delicious blooms are characteristic of what we conjure when we think of zinnias, only super-sized. Direct sow this zinnia to attract and support pollinators.
‘Queeny Lime Red’
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botanical name Zinnia elegans ‘Queeny Lime Red’ |
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sun requirements Full sun |
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height 30-40” |
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hardiness zones 2-11 |
The ‘Queen’ series of zinnia is a favorite for bold color, form, height, and lasting flowers. ‘Queen Lime’ is a beautiful foil for other blooms with lime-to-pale green shades. It creates an elegant neutral with fully double flowers and a tidy, rounded form.
‘Queeny Lime’ is a longtime favorite for its tall blooms on sturdy stems. It performs well in high heat and humidity with good disease resistance. ‘Queeny Lime Red’ offers a twist with burgundy red outer petals that transition to lime at the center. ‘Red’ is a Fleuroselect Novelty award winner. Another standout in the family is ‘Queeny Lime Orange,’ an All-America Selections and Fleoroselect Gold Medal winner. ‘Orange’ shows shades of peach and coral with lime centers.
