How To Grow Cosmos From Seed

Flower farms and backyard cut flower gardens are going crazy for cosmos, it would have to be our most popular flower variety to grow. Here's some simple tips to grow your best cosmos from seed! 

Cosmos are a super easy flower to grow and will bloom 12 weeks after you sow! Best sown from Spring to Summer.

Sowing + Germination Tips: 

  • Once frosts have passed, start seeds in a greenhouse like environment for the first 6 weeks.
  • Sow the seeds in punnets, just cover the seeds with soil, it doesn't matter which way the seed is up - as long as it is vertical. 
  • Grow the seedlings at 20-22 degrees.
  • The seeds will germinate at around 7-10 days. 
  • Alternatively cosmos can be sown direct after frost have passed and then thinned out to 20-30cm apart. 

Planting Tips:

  • After six weeks of growth, the seedlings are ready to begin to venture into the outside world. Start by letting them spend 1 hour a day, working up to 5 hours over a week. This is called 'hardening off'.
  • Pinch out your cosmos seedlings when they are 30cm tall (3 true sets of leaves). Pinching out means taking the top 10cm off your seedling. This will encourage a bushier foliage, and more flowers! If you do not pinch the seedlings it may result in excessively tall plants with less flowers.
  • Taller varieties such as the sensation may need netting for support, to avoid being damaged in wind.
  • Cosmos like full sun and well draining soil. 
  • Once the plants are established, they do not need a lot of water. 
  • Deadheading your cosmos will keep a continuous supply of blooms to be enjoyed over Spring and Summer. 
  • Too much nitrogen in the soil can result in unhealthy plants and fewer stems.
  • From seed to bloom takes around 8-12 weeks. 

Harvesting Tips:

When the petals are just opened, but not yet flattened. 

They last about 4-7 days in a vase.

Cosmos is an annual flower but the seeds can be saved for next year by letting the flower die back and the petals will fall off - the seeds will then form. They will be ready to harvest once the head has completely opened and brown and dry. They need to be 100% dry before storing, they can then be labelled and put in an airtight container, ready to be sown again next year!

Cosmos seeds are open pollinated, this means they are a non-hybrid type of seed that can reproduce itself to have similar traits to the parent plant from one generation to the next. If you are saving the seeds, as long as pollen is not shared between two varieties of the same species, the seeds should remain true to type year after year.

Our top most loved Cosmos Varieties:

Cosmos Cupcake flowers in different shades of blush in colour, and make an absolutely stunning cut flower. 

A small percentage of flowers have lovely, tufted centres. The cupcakes are a mix of singles and semi doubles + some will be solid and some will be streaked. All cosmos cupcakes bloom differently, a small percent of the plants may come through white cosmos cupcakes. Nature is so beautifully unique and different! 

Cosmos Apricotta - a new variety in an amazing apricot shade with rose centres. A must grow!

Cosmos Apricot Lemonade - a sweet peach and yellow variety with a soft pink centre. 

Cosmos Double Click + Double Dutch Bon Bon - semi doubles and doubles in a range of straight + bi colours.

Cosmos Fizzy - sweet tufted centres.

Cosmos Seashells - unique tuber petals.

Cosmos Sensations - simple and sweet single daisy like blooms in pure white, pink and mixed.

Cosmos Popsocks - a brand new variety that has some anemone heads as well as singles and doubles. 

Cosmos Double Click Snowpuff

Cosmos Purity White 

Cosmos Picotee

Cosmos Seashell

View all our Cosmos Varieties.

Frequently asked questions about growing cosmos flowers:
Why are my cosmos seedling leggy?
If your cosmos seedlings are legging this means they are lacking sunlight.
They have become legging as they are looking for light. To stop them from being leggy put the cosmos seedlings in a sunny spot where there is plenty of sunlight all day long.
Why are my cosmos plants tall and not bushy?
Pinching out the tip of the cosmos seedlings when they are 30cm tall will encourage bushier foliage and more flowers. 
Why are my cosmos not flowering?
Cosmos love sun! Making sure they are sown or planted in a full sun position will help encourage growth and flowers.
When to sow cosmos in Australia?
Spring to mid summer in most areas and can also be planted over winter in warmer areas of Australia.