How to Grow Zinnia Flowers

My tips for growing gorgeous zinnias!

Different types

The full name for the zinnia flowers we know and love is zinnia elegans. It is native to Mexico but is grown around the world. According to the University of Wisconsin-Madison, there are 13 different species of the zinnia genus.

However, that doesn’t mean there are only 13 different species of zinnias. There are A LOT of zinnias. One different species of zinnia might have a bunch of different varieties, cultivars, and hybrids. Flowers on zinnias can also have different shapes and sizes.

Here are a few different more common zinnias you’ll likely encounter:

• Zinnia elegans, the classic—it is tall and upright with wide leaves and large flowers
• Zinnia angustifolia—a smaller, bushier variety that produces orange, yellow, and white flowers
• Profusion zinnias—I fell in love with these last summer! They are compact but spread nicely about a foot wide. The colors can be pink, red, orange, and more.
• Zahara zinnias—these disease-resistant zinnias have large flowers in a lot of colors. Some even produce double blooms.

Sun requirements

Zinnias are full sun plants—that means 6+ hours of sun per day for the best blooms. Plant them in your sunniest spot. However, I have experimented with planting zinnias in different locations with varying light levels.

For example, I planted profusion zinnias in my front garden, which is more of a morning sun space. They went absolutely nuts all spring, summer, and early fall! So don’t rule zinnias out if you don’t have a ton of sun.

Height & support

The different types of zinnias can have very different growth patterns. The more common zinnia elegans variety can grow to be up to 3 feet high and 1-2 feet wide (depending on pruning). Other smaller varieties of zinnia like profusion zinnias don’t even reach 1 foot tall. Instead, they spread a bit more.

Taller types of zinnias make a great choice for the back of a garden or along a fence, and they will generally grow strong enough to support themselves. However, if you’re growing a large number of flowers in a cut flower garden, you may choose to add some support. You can use a bamboo stake and twine to prop a plant up. Or you can use cut flower support cages or netting.

When you purchase your zinnia seeds or plants, just look on the label to see exactly what type you’re buying. It will tell you how large they’ll grow so you can plant accordingly.

When to plant

Zinnias are sensitive to frost. Don’t plant them in the ground until your last frost date has passed (Google to find yours since they are different everywhere).

You can get a jump start on your seeds indoors. Simply pop a seed or two into a small cup with soil. Give the seeds plenty of sun; consider a sunny window or a grow light with a heat lamp.

Then, when the plants are large enough to be transplanted and your last frost date has passed, move them to the garden. This is what I did this last summer.

You can also just scatter your zinnia seeds, which I do, too. You can sprinkle more seeds than you need, though. Then, once they sprout, just thin them out to adhere to the required spacing. This way, you won’t have any large gaps if a seed or two fails to germinate.

When you do scatter them, simply cover with an inch or so of soil or compost and let nature do its thing. These plants are so resilient that I often get volunteers from flowers that dropped seeds the previous season!

In-ground vs. pots

Zinnias can do quite well in pots. I would recommend planting only the smaller varieties in pots, though. The taller varieties like zinnia elegans can get quite top heavy, and a larger root system anchored in the ground can help.

I have planted taller zinnias in large pots before, and they never did as well as the same plants I had planted in the ground. When planting anything in pots, also make sure to monitor the soil moisture since the water evaporates faster in pots.

Growth rate & blooms

Zinnias grow quite quickly. If you start the seeds indoors, you should notice that your plants sprout in only 1-2 weeks. It will be a number of weeks to a month or so before you see your first flowers.

Zinnias also bloom all summer. They will likely begin blooming in the late spring. Mine usually explode in size and flower production around late June/early July here in Maryland and continue to do so right up until the first frost.

Don’t shy away from cutting your zinnias to make arrangements, either. When you cut your zinnia flowers at the stem, the plant will respond by sending out a new stem that will produce a flower. This helps to encourage a fuller plant and more flowers.

While the plants last up until the first frost, the individual zinnia flowers do not last that long. You’ll notice some of the flowers begin to dry, brown, and die off about midway through summer. This is okay. Simply prune the flowers off as they reach their end of life—consider this deadheading.

You’ll likely notice more dying flowers as the season progresses. In early September, I did a large pruning of my taller zinnias. The smaller profusion plants required very little pruning all season.

Hardiness

Zinnias are annuals, which means that they must be replanted every year. However, as the flowers die off, they will drop their seeds. Depending on your climate, it’s entirely possible—likely, even—that the seeds will resprout in the spring.

That’s right—the seeds will live through the winter and nature will pick back up where she left off in the spring when temperatures start to rise. If you don’t want zinnias to spread, deadheading the dying flower heads helps.

Toward the end of the season when the flowers begin to decline much faster, you can also harvest zinnia seeds to plant for next year. I love harvesting seeds because, although you don’t really save that much money, it’s neat thinking about the plant continuing next year.

Saving seeds

I have a whole guide on how to harvest seeds from zinnia flowers and did a quick YouTube video showing the steps as well. Here’s a quick overview of the process.

1. Wait until the flower dries completely; there should be no color left, and it should be literally crumbling to the touch.
2. Crumble the flower heads onto a paper towel and pick out the seeds; the seeds are the little pieces that look like arrowheads.
3. Let dry for another 24 hours or so and then store in a plastic baggie or paper bag for next year.

Powdery mildew

If you notice white spots on your zinnia plant’s leaves, it’s likely powdery mildew. It is a common disease among many plants, not just zinnias. It shows itself as white to gray powdery spots on the plant’s leaves—occasionally on the stems and flowers, too.

It might not look great, but if it’s only a bit of powdery mildew, it isn’t a huge cause for concern. Zinnia plants can grow happily with powdery mildew. It just doesn’t look great, and it will spread over time.

Remember, zinnia plants are from hot, dry climates. They don’t do well with excessive moisture—whether it’s from humid air or too much rain. And we can get both of those in our Maryland summers. With that in mind, keep these tips in mind to prevent powdery mildew from setting in.

• Good air circulation can help to prevent powdery mildew infestations. Don’t plant your zinnias too close together, and consider pruning if they are really going bonkers growing.
• Water the base of the plant, not the leaves; water in the morning so the hot summer sun can quickly dry out the leaves.
• Choose varieties that are resistant to powdery mildew like zahara zinnias and profusion zinnias.

In conclusion…

As we wrap up here, I wanted to provide an overview of the key things I want you to remember when growing zinnias. They are a rewarding plant that I’m sure you’ll be happy you added to your garden!!

• Easy to grow, resilient, and great for new gardeners.
• Many different varieties that can grow between 1 and 3 or more feet tall
• Requires full sun (6+ hours/day) for best blooms.
• Plant seeds outdoors after the last frost or start indoors several weeks before the last frost.
• Suitable for pots, but larger varieties thrive better in the ground.
• Blooms all summer, and cutting flowers generally promotes more blooms.
• Replant annually, but seeds can self-sow or be harvested.
• Help prevent powdery mildew by avoiding crowding plants and watering in the morning at the base of the plants.

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