How To Save Cosmos Seeds

Last updated on March 27th, 2023 at 08:10 pm

Saving cosmos seeds is an easy and economical way to preserve the seeds of this sweet romantic flower to plant in your flower garden the next growing season. Learn how to save cosmos seeds to continue to grow these cottage garden plants in your garden year after year.

a cosmos plant with multiple stems and seed heads harvested for seed collection, on a wooden railing, showing how to save cosmos seeds — how to save cosmos seeds- a cosmos plant with multiple stems and seed heads harvested for seed collection

Cosmos is an annual flower that gets planted in our garden every year.

It is a low-maintenance flower and makes a wonderful cut flower with a good vase life when picked in the right stage of growth.

Cosmos make a great addition to cut flower and cottage gardens.

The blooms are airy and ethereal, and always a pleasure to grow. The leaves are lacy and fine and soft to the touch.

pink cosmos blooms growing in the garden — cosmos blooms are delicate and airy and there are many varieties to chose from

deep pink cosmos growing in the garden — we grow lots of cosmos at the flower farm

For us it has many uses, as both a great flower and as well as a feathery filler.

I find myself growing more cosmos every year for this reason.

Saving Seeds Is Beneficial

Saving seeds helps to save on some costs for future crops, however it is much more than just that.

By saving the seeds of your plants you are actually saving the seeds of the most adapted plants in your garden, that have bloomed and then set seed.

These plants have grown in your own environment, and endured your weather patterns throughout the growing season.

If you harvest flower seeds and save your seed from year to year, over time the seeds will become more hardy and adapted to your garden space.

Cosmos seed is no exception.

We harvest and save cosmos seeds after every growing season, and plant them out again the following spring.

Cosmos are some of the easiest flowers from which to save seed.

pink cosmos flowers growing in the garden against a blurred background — cosmos has some of the easiest flower seeds to save

Where Are The Seeds In Cosmos?

Cosmos seeds are located in the centre disc of the flower. Seeds will form on the flower if pollinators fertilize the tiny florets growing within the centre disc.

a pink cosmos bloom with a bee harvesting pollen from the centre disc florets — cosmos seeds will form in the centre disc if the flower is fertilized- a bee harvesting pollen from the centre disc florets

After blooming, the cosmos flowers will lose their colourful petals which surround the disc, as the seeds inside the disc begin to mature.

Cosmos tends to produces numerous flowers in different stages of growth, so you can often find mature seed pods on the same stem with fresh blooms.

I usually wait until the end of the season, and harvest at that time.

a hand holding dried cosmos seed heads after harvesting — cosmos seed heads after harvesting

What Do Cosmos Seeds Look Like?

Cosmos seeds are light beige or brown in colour, and are elongated with a narrowing at each end.

The seeds measure approximately five to six mm in length.

The seeds are contained within the dried centre disc at maturity, along with white chaff and other plant debris. Mature seeds will fall easily out of the seed head at the slightest touch.

cosmos seed heads and seeds on a wooden railing — cosmos seed heads and seeds

cosmos seeds on a wooden railing — a closeup of cosmos seeds

cosmos seeds on a ruler against a pink background, showing that they are approximately 0.5 to 0.6 mm in length — the seeds of cosmos are approximately 5 to 6 mm in length

It is important to allow cosmos seeds to mature on the plant to get viable seeds for harvesting.

When the pod is mature, the seeds will just fall away from the pod with a simple touch.

For this reason , if you are planning to save the seeds for future planting, make sure to collect the seeds before they spill into the garden.

Generally there are always a few mature pods on each plant at the end of the season, even when some pods have lost their seeds.

cosmos stem on a wooden railing at the end of the season with various stages of seed pod formation — cosmos stem at the end of the season with various stages of seed pod formation- they are not all mature, and some have lost seeds

Tools For Harvesting

Container for collection, such as a seedling tray, a bowl, or a brown paper bag

Pair of sharp scissors or snippers

Labels to identify the seeds, such as a post it note to stick to the inside of the container, or a marker to write on the outside of the bag.

Harvesting Cosmos Seed

Harvest cosmos seed at the end of the growing season in early fall, when the seed heads have matured and you notice that the seeds become loose and begin to fall away from the pods.

a hand holding a mature cosmos seed head with seeds — harvest cosmos at the end of the season when the seeds fall away from the pods or seed heads

a hand holding a cosmos seed head with cosmos seeds falling out of the seed head — cosmos seeds falling out of the seed head

Harvesting at this stage is ideal, and the seeds should be viable.

Chose a dry day on which to harvest so that the seed heads will be dry. This is important to help prevent moulding of the seeds.

Place your label inside or on your container. This is especially important if you are going to be harvesting more than one variety. It is very easy to mix seed heads up if they are not identified, as they often look similar.

flower seeds and stems in a black cell tray with paper labels, showing that labeling the seeds is important for identification — labeling the seeds is important for identification

For the collection you have several options:

You can cut stems from the plant with multiple seed heads on each stem, or

You can cut the individual seed heads and leave the stems in the field or garden.

I have done it both ways, depending on how many other flower seeds I also intend to harvest on that day.

Harvesting the stems with multiple seed pods is the fastest way, although you do have to separate the seed pods from the stem on the other end eventually when you bring them inside.

cosmos stems with multiple seed heads and seeds on a wooden railing — harvesting cosmos stems with multiple seed heads is the fastest way to collect the seeds

Removing The Seed From The Cosmos Seed Head

Removing the seeds from the cosmos seed head is extremely easy, because the seeds are right there, mixed in with a bit of seed chaff.

When the seeds are fully ripe, just brushing the seed pod with your finger will dislodge the seeds from the seed head.

Hold each flower head over a container and give them a rub, allowing the contents to fall into your container.

a hand holding a cosmos seed head — the cosmos seeds are easy to remove from the seed head

a hand holding a cosmos seed head on a wooden railing, demonstrating that the seeds and chaff fall out easily from the seed head — the seeds and chaff fall out easily from the seed head

Separating The Seeds from The Chaff

There is a bit of chaff with the cosmos seeds, although it is quite easy to distinguish the seed from the chaff. The seeds are easily picked out manually with a pair of tweezers.

It’s always a good idea to clean the seeds and remove as much chaff as possible before storing.

tweezers holding a cosmos seed against a blurred background — separating cosmos seed from the chaff with tweezers is easy

Drying Cosmos Seed

To dry the cosmos seeds, spread them out on a surface so that they can air dry.

I usually use a plate or a tray. A baking sheet is also an option if you have lots of seeds.

Dry seeds for a couple of days before storing away.

Storing Cosmos Seed

Cosmos seeds can be stored in paper envelopes or Kraft bags, which will help to keep them dry.

Make sure to label your envelopes with the seed type and variety, along with the date, which should include the year as well.

For best results, store seeds in a cool dark place in a dry location.

The seeds will last for a few years or even longer given the right storage conditions.

cosmos seeds in a paper bag on a wooden railing — store cosmos seeds in an envelope or bag and record the harvest date

How Long Can You Keep Cosmos Seeds?

Cosmos seeds will last from three to five years in storage if kept in ideal conditions.

Here is a great reference from Johnny’s seeds which includes a table with viability times for different seed types:

How Long Can Seeds Last In Storage?

We usually don’t keep our seeds for this long, as we generally collect fresh seed every season, and plant out new plants the following year.

However, you may want to gift a few packages, or have some on hand for future years. It’s always nice to know that you can save your cosmos seeds for a few years, and that they will last for a while.

Will Cosmos Reseed Itself?

Cosmos does reseed, although not excessively in our zone 5b garden.

pink cosmos flowers and leaves in the garden — cosmos will readily reseed if it likes it’s location

Whenever I find a volunteer cosmos plant, I am always happy to discover it. I generally let these self sown plants continue to grow wherever they have put down their roots if I possibly can.

Sometimes however the cosmos will pop up in spaces where the plant has to be moved, such as in a row where I have laid landscape fabric in which to plant another plant.

The tiny cosmos seedlings are easy to identify by their leaves, and occasionally will shoot up inside one of the holes in the fabric.

When this happens I will just dig them up and relocate them to another area in the garden.

pink cosmos flowers in the garden — cosmos plants are easy to relocate

Conclusion

Cosmos are great cut flowers, and they will always have a place in our cutting garden.

Saving cosmos seeds is a fun and easy activity for the end of the gardening season. It’s a great way to perpetuate these beautiful flowers in your garden year after year.

Seed saving is also economical, since the seeds saved are essentially free seeds straight from the garden.

Having the seeds from your own garden and the seed collection process is a wonderful experience. Keep in mind however that not all seed will come true to the parent plant.

If you have other cosmos varieties growing in your garden, the flowers will be open pollinated, and you may end up with different varieties of flowers, and even new hybrid plants.

Enjoy the fruits of your garden, save some cosmos seeds, and enjoy your sweet cosmos plants.

How To Save Cosmos Seeds – Harvest And Storage

Saving Seeds Is Beneficial