How to Sow Amaranthus: Adding Height & Drama to Your Dahlia Garden

Amaranthus is one of our favourite annual flowers to grow alongside dahlias, bringing height, texture and dramatic colour to the summer garden.

We love growing amaranthus alongside our dahlias and annual flowers on the Dahlia Beach farm. The deep colours and unusual shapes bring contrast and movement to the fields - and they make a wonderful addition to our cut flower harvest throughout the summer.

This year, we’re excited to be including our very own amaranthus seeds with every dahlia collection — lovingly collected from the annuals grown on our farm last summer.

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

What Are Amaranthus?

With its striking tassel-like blooms and rich, velvety colours, amaranthus is a plant that adds something truly special to summer borders and flower arrangements. Some varieties produce long, cascading trails that spill beautifully downwards, while others form upright plumes that create height and structure among softer flowers.

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 Amaranthus Seeds

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

You have two options with sowing amaranthus 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 seeds indoors will give plants a helpful head start before planting them into the garden.

What You'll Need to Grow Amaranthus

Amaranthus is a wonderfully rewarding flower to grow from seed, making it a great choice whether you’re new to sowing annuals or already love growing your own cut flowers. It’s one of the reasons we love including it in our Dahlia Beach collections.

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

• Small pots or seed trays

• Good quality seed compost

• Your Dahlia Beach amaranthus seeds

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

Step-by-Step: How to Sow Amaranthus Seeds

Amaranthus seeds are very small, but they germinate readily when kept warm and lightly moist. 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 or vermiculite.

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 30–40cm apart. Amaranthus grows quickly once established and can reach impressive heights by mid to late summer.

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

Final Tips (& Common Mistakes to Avoid!)

• Don't sow too early! Amaranthus prefers warmth, so seeds may struggle if temperatures are too cool. If you intend to start them indoors, make sure they’re kept somewhere warm and bright.

• Don't plant in shade. These plants love warmth and grow best in full sun, where they develop strong stems and rich colour.

• Don't overcrowd them. Amaranthus can grow quite large, so giving these plants enough space helps them develop strong, healthy stems.

With sunshine, warmth and a little space to grow, amaranthus will reward you with beautiful, dramatic flowers throughout the summer months.

Growing Amaranthus Alongside Dahlias

Amaranthus makes a beautiful companion plant for dahlias. Its tall stems and dramatic blooms bring contrast and texture to borders, creating a layered and abundant summer garden.

As dahlias begin to bloom, the cascading tassels or upright plumes of amaranthus add movement and depth to the garden. Together, they create the kind of flower-filled garden we love — full of colour, texture and flowers to enjoy throughout the season.

Happy Growing!

There’s something incredibly special about growing flowers from seed — nurturing a tiny seedling and watching it flourish into a plant that fills your garden with colour and movement throughout the summer.

The Dahlia Beach amaranthus 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.

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 beautiful plants bring height, texture and 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.