How to Sow Zinnias: A Simple Guide to Growing the Perfect Companion for Dahlias

With their bright, cheerful faces and a long flowering season, zinnias are a favourite for both beginner gardeners and seasoned flower growers alike. They bloom generously throughout summer and are perfect for cutting, which means you can enjoy them both in the garden and in a vase (alongside your dahlias of course!).

We love planting zinnias alongside our dahlias on the farm, as their vibrant flowers attract pollinators and add another layer of colour to the fields as the season unfolds. And this year, we’re excited to be including our very own zinnia seeds with every dahlia collection purchased - originally planted in 2024 from Floret Seeds*. Over the past two years they have cross-pollinated with other zinnia varieties, to produce an especially diverse range of colours, forms and personalities.

If you’ve received a packet, here’s our simple guide to sowing and growing your zinnias.

What Are Zinnias?

Zinnias are known as annual flowers, which simply means they complete their entire life cycle in one growing season. From seed, they grow into plants, produce flowers, set seed and then naturally finish when the colder weather arrives in autumn.

While they don’t return the following year like perennials, annuals are wonderfully generous plants. They grow quickly, flower abundantly, and provide months of colour throughout summer.

When to Sow Zinnia Seeds

Like dahlias, zinnias are warm-loving flowers - so they’re best sown once the weather begins to warm up.

You have two options with sowing zinnia seeds. You can either start them early indoors from late March/early April to give them a head start (a bit like starting dahlias in pots) - or, you can sow them directly outdoors from late May/early June, after last frost. Starting them indoors gives them a head start, but zinnias are also very happy when sown directly into the garden.

What You'll Need to Grow Zinnias

Zinnias are wonderfully straightforward to grow, making them perfect if you’re new to sowing flowers from seed. It's why we love to include them in our collections!

To sow your zinnia seeds indoors, you’ll need:

• Small pots or seed trays

• Good quality seed compost

• Your Dahlia Beach zinnia seeds

• A warm, bright spot, such as a windowsill or greenhouse

Step-by-Step: How to Sow Zinnia Seeds

Follow these steps and you should begin to see seedlings appearing within 5–10 days:

1. Fill your pots or seed trays with compost and gently pat down.

2. Place your seeds on the surface, spacing them slightly apart.

3. Cover lightly with compost. Zinnias only need a thin covering.

4. Water gently. Keep the compost moist but not waterlogged!

5. Place somewhere warm and bright to encourage germination.

Once your seedlings have developed their first few true leaves, you can either pot them on into larger pots, or transfer them directly into the ground outside (after last frost). However...

6. Before transferring them outside, make sure to allow your young plants to gradually adjust to outdoor conditions by placing them outside during the day for a week or so.

7. When planting out, choose a sunny spot with well-drained soil and space plants around 25–30cm apart. Zinnias love warmth and sunshine, and the more sun they receive, the more flowers they will produce.

Like dahlias, you should water them regularly but avoid overly wet soil.

Final Tips (& Common Mistakes to Avoid!)

• Don't sow too early! Zinnias love warmth, so sowing them too early when temperatures are still cool can slow germination. If you intend to start them indoors, make sure they’re kept somewhere warm and bright.

• Don't plant in shade. These cheerful flowers are real sun worshippers. For the best blooms, plant your zinnias in a sunny spot where they’ll receive plenty of light and warmth throughout the day.

• Don't overwater. While seedlings need consistent moisture, overly wet soil can cause problems. Keep compost lightly moist rather than soggy.

• Pick them regularly. One of the joys of growing zinnias is that the more you cut them, the more they flower - making them a wonderful addition to any cut flower garden (and the perfect pairing for your dahlias). Regular picking encourages the plants to keep producing fresh blooms all summer long.

With plenty of sunshine, a little space to grow, and regular harvesting, your zinnias will reward you with months of bright, joyful flowers.

Growing Zinnias Alongside Dahlias

Zinnias make the perfect companion to dahlias in the summer garden. Both flowers thrive in sunny positions and well-drained soil, and together they create beds and borders bursting with colour throughout the season.

Because zinnias grow quickly from seed, they’re a wonderful way to fill spaces between your dahlia plants while they establish earlier in the season. By midsummer, the two flowers grow beautifully together to create an abundant, flower-filled garden.

Happy Growing!

Growing flowers from seed is a truly joyful task during the gardening season; watching tiny seedlings grow into vibrant blooms that fill your garden with colour all summer long.

This year, we’re so excited to be sharing a little piece of the Dahlia Beach farm with you, sending our zinnia seeds as part of our cut flower collections. We can’t wait to see them blooming in gardens across the country later this summer!

If you haven’t yet chosen your dahlias for the season, you can still explore our Dahlia Beach Collections, which have each been carefully selected to help you create a beautiful, flower-filled garden.

Here’s to a summer full of colour, flowers and plenty of joyful moments in the garden 🌸

*We would also like to take this opportunity to thank Erin and the team at Floret for their extraordinary contribution to flower breeding in the USA and if you don’t follow them already, click here to find out more.

Got questions or want to show off your flowers? Tag us on Instagram @dahliabeach - we love seeing what you’re growing.