How to grow Zinnias – 5 Tips for Growing Zinnias

Learn how to grow low-maintenance zinnias and add a long-lasting pop of color to your garden during even the hottest months of the year.

Butterflies, bees, hummingbirds, and other pollinators are drawn to these vibrant flowers. Zinnias make excellent cut flowers, and come in varied sizes, colors, and textures. 

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5 Tips for How to Grow Zinnias

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1. Start zinnia seeds indoors or in the garden

If you have purchased zinnias from a local nursery and been disappointed with the results, try planting them from seed instead. I use zinnia seeds from Botanical Interests.

I’ve had the most success starting zinnias indoors in seed trays just a few weeks before the last frost date. I use these seed starting trays from Bootstrap Farmer. I transplant them into the garden when they are a few inches tall.

The best time to plant zinnias is in late spring after the last frost has passed and the soil has warmed up. Typically, this is around late April to early May in most regions, but it may vary depending on your local climate. Zinnias thrive in warm weather and full sun, so planting them at the right time ensures they grow strong and produce vibrant blooms throughout the summer.

In the low desert of Arizona: 

• Start seeds indoors:
• February – May
• Plant seeds or transplants outside:
• March – June
• Zinnias bloom from April to November.

To start zinnias from seed (indoors or outside), poke the pointy end of the seed into the soil and then cover it lightly with soil.

Sow zinnia seeds about 1/4-inch deep and space them 6-12 inches apart, depending on the variety. For larger varieties, allow 12-18 inches between plants. This will ensure proper air circulation and reduce the risk of diseases.

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2. Care for zinnias as they grow

Plant zinnias in rich soil amended with compost and organic fertilizer. Choose well-draining soil with a pH between 6.0 and 7.0. Amend the soil with compost or aged manure to improve fertility and drainage if needed. Zinnias don’t need supplemental fertilizer throughout the season.

I love planting zinnias along the edges or borders of garden beds, where they add beauty and attract pollinators.

Give zinnias plenty of sun. Zinnias grown in the shade are often leggy and susceptible to mildew. 

Zinnias do not like getting their leaves wet. Use drip irrigation rather than spraying them overhead. Water can cause problems with powdery mildew. Zinnias prefer consistent moisture but don’t like to be over-watered. Water them deeply once or twice a week, depending on your local climate. Avoid overhead watering to prevent leaf diseases.

Taller zinnia varieties may require staking or support to prevent them from toppling over in heavy rain or wind.

Watch for pests such as aphids, spider mites, and caterpillars. Treat any infestations with organic solutions. To prevent fungal diseases like powdery mildew, ensure proper spacing and avoid overhead watering.

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3. Cut zinnias back when young for more blooms

I recommend cutting back zinnia seedlings to encourage more blooms and create bushier plants. For most zinnia varieties, start pruning when the seedlings are about 6-8 inches tall. Use clean, sharp pruning shears or scissors to make the cuts.

To properly prune zinnia seedlings, pinch or cut off the top 1-2 inches of the main stem just above a leaf node or set of leaves. This will stimulate side branching and result in a bushier plant with more flowers. Make sure to remove any weak or leggy growth, leaving only strong and healthy stems.

Prune your zinnias periodically throughout the growing season to maintain their shape and maximize blooming potential.

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4. Harvest flowers often to encourage more blooms

Cut zinnia flowers in the morning when they are fully open for the longest vase life. Zinnia blooms don’t continue to open once cut. Harvest flowers when the petals are open and the stem has stiffened. Zinnias are an excellent cut flower and last up to 10 days in a vase with a floral preservative. Change the water in the vase every couple of days to keep them looking fresh.

If you are not harvesting the blooms for cut flowers, keep the spent flowers deadheaded to encourage the plant to produce new blooms (not seeds).

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5. Save zinnia seeds each season

To save and store zinnia seeds for future planting:

1. Begin by allowing a few of your healthiest blooms to mature fully and dry out on the plant.
2. Once the flower heads turn brown and become brittle, carefully snip them off with clean, sharp scissors or pruning shears.
3. Bring the flower heads indoors and place them in a well-ventilated area to continue drying for a week or two.
4. When fully dry, gently break apart the flower head, revealing the arrowhead-shaped seeds attached to the base of each petal. Separate the seeds from debris and allow them to air-dry for another day or two.
5. Store the seeds in a labeled paper envelope or small glass jar, ensuring they are completely dry before sealing. Keep the container in a cool, dark, and dry location, such as a cupboard or closet, until you’re ready to plant the seeds in the next growing season.

This method preserves the genetic diversity of your zinnias and allows you to enjoy their vibrant blooms year after year.  Read this blog post to learn more about how to save seeds. 

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