How to Grow 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

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.

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. Space plants 6” to 18” apart depending on the variety to maximize air circulation and reduce powdery mildew.

2. Plant zinnias in the right location

• Plant zinnias in rich soil amended with compost and organic fertilizer. Zinnias don’t need supplemental fertilizer throughout the season.
• 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.
• I love planting zinnias along the edges or borders of garden beds, where they add beauty and attract pollinators.

3. Cut zinnias back when young for more blooms

This tip for how to grow zinnias will make the biggest difference in the number of blooms. When the young zinnia plant is 18 inches tall, cut the central stem just above 2-3 side shoots. This early pruning encourages multiple stems rather than one.

Flowers to Plant Outside & Seeds to Start Indoors Each Month in the Low Desert of Arizona.
• PLANTING GUIDE: Each month lists annual flowers and bulbs to plant outside & seeds to start indoors.
• BLOOMING GUIDE: Photos show what may be in bloom that month.

4. Harvest flowers often to encourage more blooms

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.

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).

5. Save zinnia seeds each season

At the end of the season, leave the blooms on the largest, prettiest flowers. Let the flower head dry completely on the plant. Seeds are ready when the flower head is dry and brittle. The petals will dry and fall away. The seeds are the large plump center of the flower head. Read this blog post to learn more about how to save seeds. 

Harvest the seeds to plant in your garden next season and to share with friends. Teach your friends how to grow zinnias too. 

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