How to Plant Zinnia Seeds
The Spruce / Candace Madonna
If you have dreams of growing an organic garden from A-Z, you may want to start at the end with some easy-growing, gorgeous zinnias. With broad blossoms, bright colors, and next to nothing to worry about ruining your tending efforts, zinnias are some of the easiest and most rewarding flowers to grow. Learn how to plant zinnia seeds for the best return and make a major impact on your garden or landscape this year.
Types and Varieties
Considering the height, color, and shape combinations, there are dozens and dozens of zinnia varieties to choose from. Since it’s so easy to collect seeds from zinnia plants, try sticking with heirloom varieties that will produce reliable replicas year after year. Still, there are lots of options when deciding which zinnias to plant.
Zinnias come in a range of shape types, including varieties that resemble daisies or dahlias, tight blossoms in beehive shapes, small button blooms, and large floppy blossoms. As a quick, easy annual, you can tuck zinnias around other plants or make a full zinnia patch. Mix up height and color–have fun playing with the many options zinnias provide without having to cater to pickier plants.
Some fun varieties to check out include:
- ‘Envy’–bright, chartreuse green blooms
- ‘Carousel’–multicolored and sturdy
- Burpee ‘Rose Giant Cactus’–with a vintage feel and full, pointed petals
- ‘Will Rogers’–with shocking red, large blooms
Zinnias do best in full sun, so gather your collection of zinnia seeds, choose your space(s), and get ready to start your spring zinnias.
How to Start Zinnia Seeds
As a full sunflower that likes warm weather, zinnias need the air and soil to be warmed to the 70s F to germinate and begin to thrive. Unfortunately, they also dislike being transplanted. That doesn’t mean you can’t make the most of the growing season, though. You still have a choice between starting zinnia seeds indoors or sowing seeds directly outdoors.
Sowing Seeds Outdoors
The easiest way to start zinnias is to plant them directly in their final beds outdoors. It takes air and soil of more than 70 F to germinate well, so wait until spring is firmly in place before planting zinnia seeds. Plant them about 1/4” right in the ground, spaced as much as your chosen variety needs, anywhere from a couple of inches to a couple of feet. Once they sprout, thin them carefully to encourage the strongest to thrive. Give enough space so that air can flow around the mature flowers, preventing disease.
Starting Seeds Indoors
If you want a jump on the growing season for some early spring color, you can get around zinnia’s aversion to transplanting. Start seeds in potting soil and peat pots about a month before the last frost. Once the soil is warmed enough for zinnias, you can plant the entire pot in the ground for an easy transition.
Zinnias like well-fed soil, so some compost worked into the ground early in the season will give the soil an edge before it’s time to get the zinnia seeds or plants in the ground. Moisture is important in early weeks, but make sure it doesn’t get soggy.
Zinnias will last for around two months, so stagger multiple plantings in the garden to keep zinnia flowers in the garden from spring through fall. Heavy humidity might be your only obstacle to constant zinnias all summer long.
Growing Beautiful Zinnias
It’s hard to pinpoint a real challenge to growing zinnias. Resistant to pests, happy in most soils, and prolific bloomers, zinnias are very nearly “set it and forget it” plants.
Water and sunlight will keep your zinnias blooming full and frequently. Too much water, on the other hand, will risk one of the only diseases zinnias are susceptible to mildew. Keep water to about an inch a week, from all sources. And, as with most plants, avoid spraying the foliage and flowers as much as possible and not at all during the heat of the day.
If you want full, bushy zinnia plants, pinch the top of the stems off of young plants. If you want to encourage tall zinnias, stake the largest so they don’t flop over.
“Harvesting” zinnias as cut flowers will also encourage full growth, telling the zinnia to keep producing blooms until some can go to seed. Cut the stems above leave or bud nodes and the stems will keep growing and producing new blooms.
Once a zinnia plant is done, you can remove it and plant something else in its place. For heirloom varieties, let one or two go-to seed and be sure to collect them for next year. Try to save seeds from zinnia plants that are tucked behind others to avoid having dying zinnias as a focal point.
Zinnias can be planted directly or transplanted into the garden. Here's a quick guide on how to easily grow them from seeds.
Growing Zinnias Inside From Seeds
The colorful blooms characteristic of zinnias (Zinnia spp.) attract bees and butterflies to the landscape throughout the growing season. Even though zinnias are fast-growing plants, starting zinnia seeds indoors can help you get an even faster jump on the growing season, a plus if you’re growing zinnias for cut flowers. These annual flowers will grow in most U.S. Department of Agriculture plant hardiness zones, as long as they receive full sunlight and grow in fast-draining soil.
Starting Zinnia Seeds Indoors
Colorado State Extension notes that zinnia plants are best started by direct-seeding in the garden; therefore, it is best to sow the seeds indoors into 2 1/2- to 4-inch biodegradable peat pots that will break down when planted outside in the soil. Planting the entire pot reduces the transplant shock so the zinnia will have a greater chance of becoming established. If you’re growing dwarf zinnias in patio pots, however, you can simply direct-sow the seeds in the containers that you’ll move outside when the weather warms in spring.
A sterile, fast-draining potting soil containing vermiculite or perlite is best for zinnia seedlings. This type of soil will provide the stability for the seedlings while allowing enough air pockets for the roots to receive adequate oxygen. When you fill the pots, the soil level should sit 1 to 1 1/2 inches below the top to allow room for watering.
Sowing Zinnia Seeds
Starting zinnia seeds indoors in the spring, four to five weeks prior to the last average spring frost date, will produce starts mature enough for transplanting outdoors. Sowing two seeds in each pot is not required, but it will help ensure that each container produces a plant.
Zinnia seeds require a sowing depth of 1/4 inch. Water the pots immediately after sowing the seeds to induce the germination process. It’s best to group multiple pots together into a plastic flat and then cover the flat with a clear plastic lid to trap in humidity.
Zinnia Seed Germination
Zinnia seeds will germinate in five to seven days when exposed to a constant temperature of 75 to 78 degrees Fahrenheit. Placing the pots away from heating and cooling vents will reduce temperature fluctuation and soil moisture loss. The seeds require watering when the top 1/4 inch of soil begins to dry and lighten in color. Adding water to the pots slowly ensures that the seeds do not wash out. Be sure to drain any standing water collected in the tray below the pots to prevent mold from forming or the soil from becoming soggy, which can promote root rot.
Continued Care of Zinnia Seedlings
Once the seedlings emerge from the soil, the plastic lid or cover is no longer needed. Seedlings require bright direct sunlight for at least six to eight hours per day and grow best when nighttime temperatures drop to a range of 65 to 68 F. Supplemental watering when the top 1 inch of soil becomes dry will provide sufficient moisture.
Once seedlings reach 1 inch in height, thin them to one plant per pot to ensure proper spacing. Seedlings benefit from a biweekly feeding of a 5-10-5 or 14-0-14 nitrogen, phosphorus, potassium water-soluble fertilizer at one-quarter strength. The seeds should be fit for transplant into the garden after the last average spring frost date passes and soil temperatures warm above 50 degrees.
Growing Zinnias Inside From Seeds. The rounded, pompom-like blooms characteristic of zinnias (Zinnia spp.) attract bees and butterflies to the landscape throughout the growing season. These annual flowers will grow in most U.S. Department of Agriculture plant hardiness zones, as long as they receive full sunlight and …