How to Sow Cosmos: A Colourful Companion For Dahlias

Cosmos are flowers that instantly bring a sense of softness and movement to the garden. With their delicate, daisy-like blooms and airy foliage, they seem to float above beds and borders, catching the light and attracting the bees and butterflies. Flowering generously from early summer right through to first frost, cosmos are loved by gardeners and flower growers alike.

We love planting cosmos alongside our dahlias and annual flowers on the farm and we grow 6 different varieties that we have found best for picking.

This year, we’re excited to be including our very own cosmos seeds with every dahlia collection — lovingly collected from the annuals grown on our farm last summer, professionally cleaned and carefully packed by our very own Nona (we love you, Nona!).

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

When to Sow Cosmos Seeds

Like dahlias, cosmos prefer warm conditions, so they are best sown once temperatures begin to rise in spring.

Cosmos are very easy to grow and, like other annuals, 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 April/May, after last frost. Starting seeds indoors will give plants a helpful head start before planting them into the garden.

What You'll Need to Grow Cosmos

Cosmos seeds are wonderfully easy to germinate and are often recommended for beginner gardeners. It’s one of the reasons we love including it in our Dahlia Beach collections.

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

• Small pots or seed trays

• Good quality seed compost

• Your Dahlia Beach cosmos seeds

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

Step-by-Step: How to Sow Cosmos Seeds

Cosmos seeds are long and slender, almost like tiny brown needles, which makes them easy to handle and space out when sowing. Follow these steps and you should begin to see seedlings appearing within 7–10 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 . Cosmos only need a thin layer!

4. Water gently. Keep the compost lightly moist.

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 30–40cm apart. Cosmos thrive in sunshine and will continue producing flowers throughout the summer, especially when regularly picked.

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

Final Tips (& Common Mistakes to Avoid!)

• Don't plant in shade. Cosmos love sunshine and will flower best in a bright, sunny spot.

• Don't overfeed the soil. Rich soil can encourage leafy growth rather than flowers. Cosmos actually prefer slightly poorer soil.

• Don't forget to pick them! Regular picking encourages cosmos (and many plants!) to keep producing fresh blooms throughout the summer.

With plenty of sunshine and a little space to grow, cosmos will reward you with months of beautiful flowers.

Happy Growing!

You'll find the process of growing something from seed so rewarding — and we promise you'll be back to sow more next year.

The Dahlia Beach cosmos seeds included in our collections were gathered from the flowers grown here on our farm last season and have been naturally cross-pollinated over the past two seasons on our farm in Woodstock. So they are really special — and we're so excited to see them grow in your own gardens this year.

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.

We hope these pretty flowers bring a touch of Dahlia Beach magic to your own garden this summer 🌸

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