How to Grow Zinnias

Plant Profile

Zinnias are annual flowers, meaning the flowers will bloom and then go to seed. They’re native to the Southwestern United States, Mexico, and South America. The plants can adapt to other soil types, but they prefer soils that are well-draining and rich in organic matter/compost. Flowers will actually grow more quickly if the soil is amended with compost. They require full sun, grow fast, bloom heavily, and are deer-resistant.

Expect zinnias to bloom in summer and attract tons of butterflies & other beneficial insects to the garden. The flowers will bloom once on each stem and are great for cutting. Pinch of spent blooms to encourage new growth. Butterflies will feed on the nectar of each bloom.

The blooms of zinnias take one of three forms: single, semidouble, and double. The difference between each of these forms is the number of rows of petals and if the center of the flower is visible or not. Single-flowered zinnias have one row of petals and the center is visible. Semidouble-flowered zinnias have a few more rows of petals than singles, less rows of petals than doubles, and the center is also visible. Double-flowered zinnias, on the other hand, have several rows of petals, but the center is not visible.

In addition to these forms, zinnias take many shapes and sizes and can be grown anywhere from window boxes to mixed borders. Plant them near certain vegetables to attract beneficial insects while adding pops of color throughout the garden. Zinnias range from dwarf varieties that grow as low as 8 inches to State Fair varieties that grow as tall as 3 feet.

Importance and Uses

Zinnias are pretty pest and disease resistant. They make gorgeous companions in containers or borders planted with petunias, dahlias, marigolds, or asters. These plants are also wonderful companions for milkweed, as monarchs and other butterflies are extremely attracted to their colors & nectar. Honeybees benefit from the nectar & pollen of zinnia flowers, too. Bees and butterflies pollinate zinnias, while the zinnia feeds them in return. Check out this blog post to learn more about nectar plants that attract and feed butterflies.

In addition to butterflies and bees, zinnias attract a host of other beneficial insects. Ladybugs are one of these beneficial insects that will do wonders for your garden. If zinnias are planted near cauliflower, ladybugs can eat the cabbage flies that plague these vegetables. In fact, zinnias are phenomenal companions for almost any vegetable that has similar growth requirements.

These flowers repel cucumber beetles and tomato worms, so try making them companions in beds or large containers. If you’re lucky, you may also get a hummingbird or two feeding off the nectar of the blooms. In return, hummingbirds eat the flies that damage tomatoes, cucumbers, and potatoes.

Starting Indoors

If you’d like to take a small risk to get a jump-start on your growing season, these plants can be started indoors. It is preferable to start them in one large container instead of transplanting them to a new location outside, but both methods can be done with patience and a close eye.

Start zinnia seeds indoors in late winter or early spring. The richer the soil, the better, as the amount of nutrients in the soil is what makes the difference between thriving and dying. Keep zinnia seeds evenly moist in a sunny location and follow the same directions for direct-sowing. Do not water in the evenings because this will cause mold to grow on the soil surface and kill any emerging seedlings.

Slowly acclimate the zinnia seedlings to outside weather for a few hours each day once they reach about 4 inches in height. Increase the time spent outside more and more every few days. The process of “hardening off” should be done for about two weeks before transplanting or moving outside takes place. Be sure not to start hardening off your zinnia seedlings until you’re absolutely positive there will be no more frost in your area because these plants will die if frost-bitten.

Follow the transplanting directions below for store-bought or indoor-grown zinnia seedlings.

Direct-Sowing Outdoors

When direct-sowing zinnia seeds, choose an area in the garden that receives full sun (6-8 hours of sunlight per day). Ensure that the soil is well-draining and rich in organic matter/compost. Compost amendments will help the zinnias bloom vigorously and grow quickly. The minimum temperature that zinnias can thrive in is about 60°F. These plants are not frost-tolerant and will not survive if planted before the weather is just right.

Sow seeds in a prepared bed or container ¼-inch deep. Water the seeds thoroughly to tuck them in. Germination time is roughly 7 to 10 days, though some can sprout as early as 4 days. Once the seedlings are about three inches tall, thin out the weaker ones so that they’re around 4 to 6 inches apart. Refer to your seed packet to determine the proper spacing for the specific variety you planted. Zinnia seedlings need plenty of air circulation to prevent powdery mildew from forming. Keep in mind, these flowers take roughly 60 to 70 days from the day you sow them to produce any blooms.

Sow several seeds once every week until summer to continue seeing zinnia blooms until the end of the growing season. These flowers only have one bloom per stem, but can re-bloom if deadheaded and fertilized appropriately. The plants sprout and grow very quickly if the proper growing conditions are met. Water them in moderation. Fertilize zinnias every three to four weeks during the growing season with a balanced fertilizer. When fall frost approaches, let the last of the zinnias flower fully and go to seed. They well self-sow and return the following year if left undisturbed.

Transplanting

Zinnia plants do not tolerate being transplanted well. They prefer to be sown directly into a garden bed or container. If you do decide to transplant store-bought or indoor-sown seedlings, then do so very gently. Many transplanted zinnias do not flourish, but they especially will not do well if transplanted before the last frost in your area.

Transplant zinnias in the morning, not in the afternoon. When it’s time to transplant, gently loosen the root ball so that the roots aren’t tightly packed together when going into the ground. Dig a hole a little less deep than the container it came in and gently spread the roots out. Cover the roots and beginning of the stem with nutrient rich, well-draining soil and lightly pack around the stem. If the soil is packed too loosely, though, the roots can become damaged and the plant won’t be able to soak up nutrients; not too tight, not too loose is the trick. Water the plant thoroughly to tuck it in.