How To Grow Beautiful Cosmos

I absolutely love the delicate romantic flowers of cosmos growing in the garden. They are a great addition to any cutting garden, and add a whimsical touch to farmhouse bouquets. Here are some insights on how to grow beautiful cosmos in your garden for all to enjoy!

Different Types Of Cosmos

Cosmos is a charming annual cottage flower with soft lacy fernlike foliage and a simple daisy-like form. It is a wonderful cut flower, and adds a rustic romantic look to farmhouse bouquets.

There are three types of cosmos available:

1. Cosmos bipinnatus, the typical white, pink and burgundy varieties that we grow in our garden.
2. Cosmos sulphureus, the yellow, orange and red varieties native to the South (Mexico and Central and South America).
3. Perennial cosmos, Cosmos atrosanguineus, a scented herbaceous perennial known as chocolate cosmos, which is not as common or readily available as the annual varieties.

There are many different varieties of annual cosmos available.

Some of the varieties of cosmos bipinnatus that we have grown in our garden include fizzy white, afternoon white, pied piper red, double click snow puff, xsenia, purity, double click bicolor rose, double click mix, cupcake white, double click cranberry, and apricot lemonade (my absolute favorite).

Cosmos comes in three different forms:

1. singles which look like single form dahlia flowers
2. doubles with their adorable frilly double blooms, and
3. fluted which look like they have been sheared with pinking shears

The Benefits Of Growing Cosmos

• Bees and pollinators love this wonderful flower!

• Cosmos is easy to grow and requires little maintenance once it is planted in the ground.

• It is a wonderful cut flower, and we love it for this reason!

• The flower can be displayed in a bouquet all on it's own, or mixed with other cottage style flowers.

• Cosmos gives a soft airy look to any spot where it is planted in the garden.

How Big Does Cosmos Grow?

Cosmos can grow up to four to six feet tall, and two feet wide.

The plants will become bushier if they are pinched at an early stage, which promotes side growth of more stems early on.

How To Grow Cosmos From Seed

Cosmos Seeds Appearance

• Cosmos seeds are black, long and slightly curved. They vary in size but on average they are about ¼ inch long.

• We store our seeds in paper envelopes, and they keep well for several years.

Are Cosmos Easy to Grow?

• Cosmos is very easy to grow from seed.

• You can direct sow the seeds right into your garden when the weather warms up.

• Alternatively the seeds can be sown indoors six weeks before the last frost, and then planted out when the chance of all frost has passed.

• Planting them early indoors or in the greenhouse will give them a head start on flowering.

Planting Cosmos Flower Seeds

• Cosmos flower seeds need moisture and warmth to germinate. If planting directly into the garden make sure your soil temperature is warm enough, and that the soil remains evenly moist.

• If planting inside, a heat mat will help to keep your soil warm during the germination process. Keep the soil slightly moist during germination .

• Cosmos seeds do not require light to germinate, and they can be covered with ⅛ inches of soil or vermiculite

When To Plant Cosmos Seeds

• It's important to consider the flowering time of cosmos to determine when is the best time to plant cosmos seeds. Cosmos is a quantitative short-day flowering plant.

• This means is that the blooming time for cosmos occurs when the daylight hours become shortened to fourteen hours or less. Essentially, this period of time occurs towards the end of summer when the days are getting shorter.

• Your spring planted cosmos will be full of blooms towards the end of summer, as the days become shorter.

• We have definitely noticed this trend!

There Can Be An Exception To This Short-Day Flowering Time.

• This exception has to do with when the cosmos seeds are planted.

• If you sow the cosmos seeds in winter, either in a greenhouse or indoors under lights, and plant a more mature plant into your garden in spring, this mature cosmos plant should bloom during the long days of summer.

Knowing this information about cosmos can help you make your decision about planting time for your cosmos seed.

When does Cosmos Bloom?

• If you plant your cosmos seeds in spring, they will grow and bloom sparsely throughout the long days of summer. Then in late summer as the day length shortens, they will put on their best display with a plant bursting with blooms.

• If you plant your seeds in winter in the greenhouse or under lights, you will have a more mature plant to plant out in the spring. These plants are more apt to flower well during the long days of summer.

How Long Does It Take Cosmos To Grow?

• Cosmos can germinate fairly quickly if given the right growing conditions. Typical germination time is 3 to 10 days, but they can take longer.

• Days to plant maturity from seeding date is approximately 75 to 90 days.

When Can Cosmos Be Planted Outside?

Annual cosmos is a half hardy annual, so should be planted into the garden after the chance of spring frosts has passed.

If your plants look somewhat leggy when first transplanted out, take heart, they will soon fill out as they begin to take hold and grow in their new location.

Where To Plant Cosmos

• Cosmos should be planted in a well drained average soil, in a location where they will get full sun.

• Since cosmos can grow tall, giving them some protection from wind is helpful. Supporting the plants with stakes, netting or some form of corralling is also an option.

• We grow our cosmos in an open field without support. Sometimes they get blown over by the wind. Sometimes stems will break from the force of the strong winds that blow in off the water.

• The close planting space between the plants allows them to support each other.

• We plant our cosmos into landscape fabric which has holes burned for a spacing of 9 to 12 inches between plants. We do this to suppress our weeds and have had some degree of success using this method.

• Cosmos requires moisture early on when getting established. For us, the rain was sufficient to maintain adequate hydration for our cosmos, with a few extra waterings during dry spells.

• From our experience cosmos has been fairly drought tolerant as the plants became mature.

All in all the cosmos was a pretty easy plant to grow.

Pinching Out Cosmos

Pinching your cosmos plants will allow them to develop into fuller and bushier plants.

• This can feel very counterintuitive, but trust me it is worth it! It feels like you are setting your plants back, but they will quickly catch up.

• Pinch the centre growing tip of the cosmos plant when it is approximately one foot tall. Sometimes this will involve cutting off the first bud beginning to form.

• The pinching process will promote the development of side shoots on the plant. The plant will become fuller as it grows to maturity.

Then at harvest time, cut deeply into the plant to cut long flower stems. As a result of these cuts, deep at the base of the plant where the cuts were made, the plant will continue to develop more side shoots.

Cosmos is considered a cut and come again flower. The more flower stems that you harvest, the more that will be produced.

Growing Cosmos In Pots

Cosmos grow well in pots. Place your pots in a sunny location, and maintain the moisture level in the soil.

Some support for the plant in the pot may be required depending on the size of your cosmos plants. Stake as needed.

If growing the edible form of cosmos, cosmos sulphureus, place the pot close to your kitchen for quick access.

Deadheading Cosmos

Cosmos will benefit from deadheading of spent blooms.

Deadheading cosmos promotes further blooms, and pruning deeply promotes the development of more stems.

Do Cosmos Come Back Every Year?

• Annual cosmos does not come back every year. Sometimes it will reseed itself in the garden in warmer zones.

• You can harvest and save your cosmos seeds at the end of the season, to replant the following year.

• Perennial cosmos, or chocolate cosmos, is hardy to zones 7 and above. Since it is perennial, if planted in warmer zones it has the potential to come back every year.

How To Grow Cosmos For Cutflowers

• Cosmos is one of our best annual flowers for cutting in the garden.

• Cosmos flowers have a vase life of about seven days, and are best sourced in-season, either from your own garden or from a local flower farm or market, if you are planning to use them as a cut flower.

• They add such a soft romantic effect to the bouquet or vase, and they are well worth using as a cut flower.

• The best stage to harvest cosmos for the longest vase life is when the flower bud is just starting to open. Flowers that are fully open when picked will not last long in the bouquet, and I usually remove the fully opened flowers from the stem when I am harvesting.

• It's important to put freshly cut cosmos stems directly into water. Before doing this, remove about half to two thirds of the foliage before inserting the stem into the water.

• Allow the stems to rehydrate in the water. We use a holding solution to fully hydrate and condition the flowers for their best vase life, however fresh cool water in a clean bucket will also do the trick.

Use Cosmos As A Bouquet Filler

Another use for cosmos is as a bouquet filler.

• I will often use the soft fernlike foliage as a green filler in bouquets, even if the stem has buds that are still small and too immature to open.

• In this case I use the stem solely for the greenery, although the little buds will add some visual interest, as they are pretty cute!

If you have any questions or comments about how to grow cosmos, please leave a comment below!

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