The lovely flowers of cosmos plants are one of its most fantastic attractions. Even though its petals are as thin as paper, their vibrant hues shine through. The center of the Cosmos flower is often a dark color, with a ring of lighter colors around it. The term harmony in Greek is where the name originates.

It’s appropriate, as the flower’s presence is associated with calmness. Growing Cosmos is rewarding because the plant requires little attention but yields beautiful flowers.

It’s understandable to feel let down when your cosmos plants fail to bloom. Do not be concerned if your plant does not have any flowers. You may get your cosmos blooms back on track by addressing one of several potential causes. By reading this guide, you will be able to know, 10 Reasons Why Aren’t My Cosmos Flowering and How to Fix It.

10 Reasons Why Aren't My Cosmos Flowering and How to Fix It

Let’s start,

Beautiful and resilient, cosmos blooms may survive in less than perfect settings. Cosmos plants are a great addition to the flower garden and the organic vegetable garden since they attract pollinators and other helpful insects.

This annual deserves a place in your garden if it already doesn’t. Sun and heat are the perfect environments for this low-maintenance plant, which rewards you with spectacular color. The carefree nature of cosmo flowers is a plus, and their ability to transform a yard into a vibrant oasis is a definite plus.

You can sit back and enjoy the flurry of activity as bees, butterflies, and even hummingbirds visit the colorful blossoms on my cosmos plants. Moreover, you can enjoy these stunning blossoms from early July through the first frost of September.

Although cosmos are considered a low-maintenance plant, they nevertheless require your attention. They won’t be able to develop if you don’t provide the conditions necessary for their success.

What causes the cosmos not to flower?  

Some gardeners say their Cosmos didn’t blossom, but generally speaking, cosmos are easy to grow and relatively hardy. The most frequent causes of Cosmos plants are not flowering, as described below.

1. Wrong weather conditions 

Even if you give your cosmos the best possible circumstances to thrive, there are times when they won’t bloom.

Due to its preference for full sun, warmer weather, and dry summer, Cosmos is less likely to exhibit blossoms if the Spring or summer has been abnormally chilly, rainy, or cloudy.

How to fix it?

Suppose you’re growing cosmos in a container. In that case, you may get a better flower show by protecting the plant from rain, increasing the temperature and humidity indoors, and giving the plant a steady water supply.

2. Immature plants

It takes around seven weeks for cosmos to come into bloom from seed, yet we tend to get overzealous about plant bloom and neglect to account for that. It’s possible that your cosmos are not yet ready to bloom, which would explain why you haven’t seen any flowers on them.

How to fix it?

It’s best to wait until you see buds forming on the tips before you start worrying.

3. Insufficient light 

Once you know what they need, growing Cosmos isn’t that difficult of a task. One of the most important, though not the only, is ensuring your plant gets enough light. One of the essential things affecting how well your cosmos bloom is the amount of sunlight they receive. Planting cosmos in a shaded part of your garden will result in leggy plants that struggle to find enough light to bloom.

Perhaps surprising to you, cosmos plants have their origins in Mexico. Therefore, a warm environment is ideal, and they don’t mind always being in the sun.

These plants are unique amongst their kind, as they are short-day plants requiring 10-12 hours of darkness to bloom. But they also need a lot of exposure to natural light.

How to fix it?

If you want your Cosmos to bloom, move them to a more sunny spot, trim back any trees that are providing unwanted shade, or put new seedlings in a border of your garden where they will get enough sun and good drainage.

The sun’s energy gives a greater capacity to sustain plant life and provide aesthetic pleasure. Be sure to increase the amount of light reaching your plants by pruning any trees or shrubs in your garden.

4. Improper Soil Condition

Heavy clay soil is not ideal for growing cosmos since it is nutrient-rich but poorly drained, thereby encouraging foliage growth at the price of flower production.

A wet environment is not ideal for cosmos growth or flowering.

How to fix it?

Growing cosmos in pots, containers, or raised beds is preferable to doing it in soil with high clay content and requires extensive amendment.

Compared to amending a garden border, pot drainage characteristics are much more favorable, and it is much simpler to make a well-draining potting mix that favors Cosmos and stimulates flowering.

Growing Cosmos from seed is best done in the Spring, between March and April, to ensure the cosmos plants have enough time to mature and bloom before frost. However, if you’ve already started growing them in clay soil, you can try transplanting the plugs into pots to increase flower production.

5. Overwatering

Cosmos doesn’t require excessive amounts of water, even in the summer. Overwatering your cosmos will cause them to produce more leaves and fewer flowers.

If the soil is persistently saturated or marshy, the plant roots may even rot owing to a lack of oxygen, which may destroy the plant.

How to fix it?

If you want to keep your Cosmos from drowning, water it deeply once a week. Cosmos are drought-tolerant once established and require consistent watering to thrive as seedlings. Having evolved in Mexico’s dry climate, cosmos plants naturally resist drought.

Plants should water once weekly until they reach their full height to prevent overwatering. In the event of heavy precipitation in the Spring or summer, you may not need to water your plants at all that week.

To avoid overwatering, examining the soil before beginning to water is essential. Make a few shallow scratches on the soil’s surface to reveal the underlying earth. The plants won’t need to water if the soil is already damp. If the soil is dry, you should water them for an inch every week.

6. Old cosmos seeds

Although many plant seeds can store for years before planting, germination rates may decrease after a year. Planting Cosmos seeds from the current year’s crop is the standard approach.

The quality of the seed and its ability to produce a bloom may compromise by prolonged storage in less than optimum circumstances.

How to fix it?

Keep your seeds in an excellent dry spot such as a garage or a shed that helps not to become too hot or cold.

If your Cosmos failed to bloom, try starting new seeds from a trustworthy source the following Spring and planting them in whole light and well-drained soil without overwatering.

7. Excessive Fertilizer

Many people mistakenly believe that your plant will thrive as long as you add fertilizer. Giving your plant a nutritional boost could help, but too much of it could be harmful.

Cosmos do not like fertilizer since they thrive in low-nutrient sandy soils, and too much fertilizer might cause them to produce plenty of foliage but no flowers.

Therefore, fertilizer, organic feed, or even mulch is often to blame if your cosmos are tall and healthy, appearing with lots of foliage but no flowers.

How to fix it?

It is unlikely that fertilizer applications will stimulate blossoms, but cosmos may bloom in the fall if given the right conditions (whole light, well-drained soil, not too much water).

How does too much nitrogen affect not flowering Cosmos? 

The plants’ lack of enthusiasm for flowering may be due to the high nitrogen fertilization levels. While nitrogen is essential for plants to thrive, too much can be harmful. Overfertilization could be to blame if your cosmos plant produces lots of healthy-looking leaves but refuses to blossom.

How to fix it?

It may also be beneficial to provide fertilizer only when planting. Most galaxies will thrive in this setting if you supply them with organic compost. Once a month, you might use a non-chemical fertilizer, such as fish emulsion with a 5-10-10 composition to give your plants a boost.

Use a fertilizer that is heavy in phosphorus and low in nitrogen. The use of this fertilizer will encourage your plant to bloom more profusely. To promote flowering, amend the soil with bone meal or rock phosphate.

8. Short day Blooming-Cosmos 

As a general rule, Cosmos flowers best when there are fewer than 12 hours of daylight, which is why they are frequently at their finest in late summer or fall.

While full daylight is best for blooming, keeping cosmos in bright light for more than 12 hours can hinder blooming since they need a period of darkness. It occurs because the Cosmos has evolved to detect seasonal change based on the pattern of changes in day length, allowing the plant to know when to flower.

The cosmos begin to bloom as the days get shorter after the summer solstice in June in the northern hemisphere.

How to fix it?

Blossom may stunt if your Cosmos (or other short-day plants) expose to even a brief amount of light at night.

Since the cosmos need 12 hours of constant darkness to bloom, after-dark artificial sources of light such as street lights or security lights come to mind. Cosmic blooms are typically delayed by longer summer days in northern latitudes, extending their season into early autumn.

Blocking away light sources (with horticultural fleece or something similar) can help to stimulate blossoms at any time during the Spring or summer, or you can wait till late Summer or Fall for flowering.

9. Incorrect planting timing

Unlike many spring flowers, cosmos blooms bloom when days are shorter. If you need the plant to blossom in the summer, you may need to plant it earlier in the year to have enough time to germinate and grow.

How to fix it?

Reduce midday light coming in. Putting a thin curtain over the plant will accomplish this. As a result, the plant will respond to the longer nights as a signal to begin flowering. It’s better to start planting indoors in the Spring so that you can move your seedlings outside when the weather warms up.

10. Nutrients abound in the soil.

Cosmos first appeared in Mexico, where they flourished in the wild on nutrient-poor, well-draining sand. The soil in the garden may be too fertile for cosmos to thrive if you’ve recently applied fertilizers like compost or manure.

Plants grown in fertile soil produce abundant, stunning foliage but comparatively few flowers, as with cosmos.

How to fix it?

With a tremendous well-draining sand and peat soil mix, your Cosmos should bloom if you treat the soil as you would for Mediterranean plants like lavender and rosemary.

Replanting your Cosmos in sandy soil is, in a nutshell, the most excellent technique to get them to bloom again. Make your sandy soil by combining perlite, vermiculite, and sand if you don’t have any on hand. To improve water flow, amend the topsoil with grit or coarse sand.

How can I get my cosmos to flower? 

What you need to know to take the best possible care of these blooms is as follows.

10 Reasons Why Aren't My Cosmos Flowering and How to Fix It

1. Provide proper sunlight. 

To thrive, Cosmos require a lot of sunlight. This plant is sensitive to the duration of the day and is at its most beautiful and prolific in the late summer and early fall when daylight hours are shorter. But if given enough time, it will blossom.

2. Deadheading and Pinching.

When your cosmos are 4-8 inches tall, pinch them to encourage side branching and a fuller plant pinch just above a cluster of leaves.

If your Cosmos is under duress, it may attempt to flower when it is still relatively tiny. To encourage additional branches and subsequent flowers, pinch off the first bloom.

Remove spent blooms from a plant as they fade to encourage new development. If you want to encourage fresh flowers, snip faded blossoms off at the stem base or even farther into the plant.

3. Water properly.

Once established Cosmos, you will not need to water your plants unless there is a protracted drought. 

Water the plants often until they are well-rooted or if the soil is dry. Make sure you don’t give cosmos too much water.

4. Use suitable soil conditions.

Inadequate amounts of organic matter can lead to uneven germination and stunted growth in the cosmos; hence sandy soil is preferable.

Although many flowering plants struggle in low-quality soil, cosmo plants thrive in this environment. They thrive in soils with medium moisture content and good drainage but can survive in relatively dry soils.

If you want your plants to stay short and bushy, avoid planting them in overly fertile soil. Staking the plants or planting them near sturdy companions might help prevent drooping.

5. Cutting the plant back.

If the flowers on your spring-planted cosmos have faded or the plant looks tired, cutting it back to a height of 13 to 18 inches can stimulate a new growth spurt that will produce flowers in late summer or early fall.

You can expect additional seedlings to emerge from the ground the following Spring if you leave the cut seed heads where they fell.

6. Keep an eye on temperature and humidity. 

Temperatures above 70⁰F are best for the cosmos, and they can tolerate high humidity levels.

7. Consider fertilizing.

The cosmic environment may suffer from fertilization. Poor soil is no problem for the cosmos. Over-fertilized plants tend to be robust and produce lots of foliage but few flowers. Cosmos plants do not require fertilizer unless they are struggling.

5 Beautiful cosmos varieties to grow in your garden

All these cosmos varieties will add color and beauty to the park while also drawing in a variety of beneficial insects and birds. There are aromatic perennials in deep, rich hues and annuals with showy blooms suitable for a vase. A wide range of popular Cosmos varieties is below.

1. Cosmos Bipinnatus’ Pied Piper Red

This cosmos variety is quite unique and beautiful with its magenta-hued inside and lavender-colored exterior. Because of its long blooming period and finely split, feathery leaves, it makes an excellent cut flower—the plant in full sun in slightly acidic and wet soil.

Grow in masses in an annual meadow with white and pink cosmos; use to cover gaps in borders with perennials like Achillea’ Terracotta;’ or arrange in a vase for a lovely display.

2. Cosmos Sulphureus ‘Bright Lights’

Semi-double flowers in shades of yellow, orange, and red, reminiscent of marigolds or geums. Floriferous from June through October and simple to cultivate in full sun and moist, well-drained soil. Vase-cutting options are available.

Collaborate with other cheerful brights (like raspberry-pink Knautia macedonica), velvet hues (such purple Salvia Viridis’ Blue Monday’ and claret Penstemon’ Raven,’ and limes (like Nicotiana’ Lime Green’) for a lively garden color palette.

3. Cosmos Bipinnatus ‘Purity

Only this kind of Cosmos belongs within the borders of your garden. Large, pure white daisy flowers with golden centers rise above beautiful apple-green foliage from June till October. Cosmos Bipinnatus Purity thrives in full sun and moist, well-drained soil and makes an attractive cut flower.

4. Cosmos Atrosanguineus Chocamocha

This dwarf variety of the plant has velvety chocolate-scented flowers and may be grown in a sunny container all summer long before being brought inside for the winter. Be sure to keep it well-watered while it is actively growing.

5. Cosmos Bipinnatus ‘Double Click Rose Bonbon’

Regarding the cosmos, this particular type is as good as it gets in terms of visual appeal. These double-pink blooms are reminiscent of satin flowers and have an air of a bygone era. Sow seeds in full sun and moist soil that drains well.

Are you cutting flowers for an indoor vase arrangement? Try scabious, verbena, and the ever-popular dahlias. In this guide, we cover several topics related to growing dahlias.

Watch How to pinch cosmos for more flowers | Video

Top 5 FAQs & answers related to 10 reasons why aren’t my cosmos flowering and how to fix it

Why are my cosmos so tall? 

You should only supplement the soil with what the plant needs. Tall, spindly Cosmos can also result from too much water. Hot and dry circumstances are indeed ideal for this flowering plant.

How long do cosmos take the flower from seeds?  

Because of how simple they are to grow, cosmos are an excellent choice for first-time gardeners. Seeds can plant indoors to gain a head start on the growing season.
However, seeds can sow immediately into garden beds once the weather warms up. The Cosmos will bloom in under three months regardless of when you plant them.

Does Cosmos come back every year?

Cosmos is a reseeder, spreading from year to year by its seeds. Cosmos will reseed itself if you let the spent flowers remain on the plant for a while.

Why are my cosmos seedlings so leggy?

Young cosmos seedlings that don’t get enough light to grow tall and leggy. Please make sure the legs hide when you transplant them. If you’re like me and your seedlings have reached for the heavens because you waited too long to replant them, try burying a good portion of the stem in the ground.

Can the cosmos grow from cuttings? 

Chocolate cosmos (rosanguineus) is a well-liked perennial that spreads from root cuttings—plant seeds or seedlings from a nursery for annuals. Annuals should be started from seed 4 to 6 weeks before the final spring frost, or they can plant directly in the garden once the danger of frost has passed.


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