Growing Zinnias From Seed - Geeky Greenhouse (2024)

We grow zinnias in the garden every single year. They’re easy-growing annuals that come in a variety of different shapes and colors. Not only are they a cinch to grow, but they also appeal to a wide range of pollinators in the garden.

Zinnias belong to the Asteraceae family and have been developed into many different cultivars and hybrids. There are so many colors, sizes, and shapes to choose from! We consider zinnias to be one of the best flowers for beginners. They’re very low-maintenance and have beautiful, prolific blooms.

You can direct sow zinnia seeds, or start them indoors and transplant them into the garden. We have done both, but we prefer to transplant them and get a head start on their growth and flowers. In this guide, I’ll explain how to grow zinnias from seed for your garden.

Step 1: Starting zinnia seeds indoors

• Start seeds 4-6 weeks before they will go outside. Here in CT, our last frost is May 1st. We start our zinnias indoors in late March.
• Sow seeds 1/4″ deep in your preferred seed starting medium or potting mix. Keep the soil warm and moist for the best germination rate. We always use a humidity dome and heating mat to help provide the best conditions for sprouting.
• Seeds should germinate around 7 days with temperatures between 70-80°F. While they do not seed sun to germinate, you should place them in the sun or under grow lights as soon as they sprout for strong plants.
• On average, zinnias take about 80 days to bloom from the day they are planted. If you start your seeds in late March like us, you’ll have blooms in June.

Step 2: Transplanting zinnia seedlings outdoors

You can purchase zinnia seedlings at the nursery and transplant them outdoors, or you can grow them from seed and transplant your own outside. I like growing them from seed so I can choose my own varieties and colors.

• Before transplanting outdoors, harden off your zinnia seedlings for 1-2 weeks. This will help them acclimate to the sunshine, wind, and other outdoor elements.
• Transplant your zinnia seedlings outdoors before they become root-bound in their pots. You may need to up-pot them if it is too cold to plant them outdoors.
• Transplant outdoors when temperatures are at least 60°F. There should no longer be a danger of frost as they are sensitive to the cold.
• Zinnias do best in garden beds but can also be grown in containers. Knowing the final height of your zinnia variety can help you determine a suitable planting location. Learn all about zinnia companion plants here.
• Spacing will depend on the variety of zinnia you choose to grow. Typically, we plant zinnias about 10″ apart, with some larger varieties needing more room to spread out. Check your individual seed packet for spacing instructions.

Step 3: Providing ideal conditions

For the brightest and most colorful flowers, you’ll want to provide zinnias with the best conditions possible.

• Zinnias like full-sun and do best with at least 6 hours of direct sunlight per day.
• Like most plants, zinnias prefer well-draining soil that is rich in organic matter. We recommend amending with compost in fall or early spring.
• Avoid overwatering your plants and try to avoid splashing water over the leaves, as zinnias are prone to powdery mildew and do not fare well with being overwatered. They prefer drier conditions.
• Fertilization is optional but may help keep your zinnias stay strong and bloom continually. Fertilize your zinnias once or twice during the growing season with a complete fertilizer (this is especially recommended for growing in containers). We prefer to amend the planting site with a rich compost that will slow-feed the plants over the course of the growing season.

Tip: Remove old blooms to encourage new growth. You can also pinch your zinnia plants to encourage bushier growth.

Want to save your zinnia seeds? Learn the whole process of saving zinnia seeds here.

Zinnias are an excellent flower to start indoors, especially for beginners. Let us know which varieties of zinnia you’re growing in the garden this year.

A few varieties we like are Zinnia ‘Peppermint Stick’ and Zinnia ‘Orange King’.