I am sure you will appreciate that sadly we cannot give individual growing advice, as unfortunately we just don’t have the time to deal with bespoke requests, with all the variables that they may include. 

We obviously want you to be successful in growing your own cosmos, so here is some advice that we hope is helpful

INTRODUCTION
Cosmos, in its annual form is native to Mexico, and is often known as the Mexican aster. It wasn’t collected until the late 1700s and the flower made its way to England in 1789, thanks to the Marchioness of Bute, wife of the English ambassador to Spain.

They are prized for their abundant, daisy-like flowers and are simple and inexpensive to grow from seeds. Plant them in full sun, providing protection from strong winds for some of the taller cultivars. Cosmos tolerates a wide range of soil types, including poor soil. Plants need even moisture to get started, but mature cosmos can be quite drought tolerant; plants produce more and larger flowers, however, if they are watered regularly. Regular and methodical dead-heading prolongs the flowering season. They will happily self-seed if required.

HABIT & CULTIVATION
Cosmos bipinnatus is a tall, bushy annual which grows up to 2.5m, with very finely divided, mid-green leaves, and large flowers up to 8cm across, usually white or pink the wide outer rays surround a central disc of tightly clustered, usually yellow, inner disc florets. They flower in late summer and into autumn, until the first frosts arrive. Many named cultivars and selections are available, including doubles, forms with tubular rays, and picotee colours. They can be grown in containers, or directly in flower beds, with some of the taller cultivars being suited to back of bed positioning. A great plant in terms of attracting pollinators such as bees to the garden.

PROPAGATION
Cosmos are a relatively simple plants to propagate from seed. Seeds can be sowed at 16°C to 20°C in the UK from February onwards, although a later sowing really can be advisable, as you will have to keep the plants frost free until planting them in situ in early May, depending on your location. Alternatively seeds can be sown in situ in late spring in a weed free bed. Remember that from whenever you sow them you are going to have to ensure the pkant gets enough light while also keeping it frost free until it can be planted out. So that can depend on where you live and what equipment - be it heated propagators, a greenhouse, and so on that you have. 

PESTS & DISEASES
Cosmos bipinnatus have relatively few pest and diseases that cannot be kept in check. New seedlings can fall foul of inquisitive birds pulling them up, or slugs, which can be combated with selective mulching products. Similarly if rabbits are an issue, they make take a liking to fresh young leaves, so protective measures may need to be employed. Cosmos can be impacted by grey mould, which can be combated by extra ventilation when growing under cover, removal of infected material, and not overcrowding with your planting schemes. Historically a fungicide has also been used in order to prevent foot rot, although there is evidence some treatments still on the market can impact pollinators.
 

AN OFTEN ASKED QUESTION IS, WHY IS MY COSMOS NOT FLOWERING?

NOT ENOUGH SUNLIGHT FOR COSMOS TO BLOOM 

Cosmos are native of Mexico and South Africa. They like the sun.

If your cosmos have been planted in a shady area of your garden then they tend to grow leggy in search of more light and with few flowers.

The amount of sunlight is one of the most influential factors for how well your cosmos flower.

NUTRIENT RICH SOIL AND TOO MUCH MTROGEN RICH FEED PREVENTS FLOWERING 

As previously mentioned, cosmos are native to Mexico where they grow wild and flower in great number in sandy soil that is low in nutrients and very well draining.

If your garden soil is rich in nutrients and has had amendments such as compost, or manure added to it recently then it is likely that the soil is too rich for cosmos to flower.

Nitrogen feed leads to cosmos putting on green growth at the expense of flowering. Essentially you are coddling your plants. A period of neglect is no bad thing. 

WATERING COSMOS TOO FREQUENTLY CAUSES FEWER FLOWERS 

Cosmos prefer a soil that is well draining and dries out somewhat after watering or rain as this is the conditions to which it is adapted. They thrive in full sun. Therefore if cosmos are to flower, you should refrain from over watering the soil.

Cosmos are very hardy when it comes to tolerating drought like conditions. If the soil is kept consistently moist then this can promote healthy foliage with few flowers.

Cosmos thrive in conditions that are fairly harsh as it is adapted to sandy soils in arid climates.

To promote flowers for cosmos that may be not flowering due to over watering, you should scale back the watering so that the soil has a chance to dry out between bouts of water.

TIMING OF SOWING CAN IMPACT BLOOMS

The optimal time for sowing seeds of cosmos is around March or April or after the threat of frost.

If you sow seeds after the optimal window of March and April then this can delay flowering for some weeks, however with patience and the right conditions the cosmos can still bloom.

Sowing in the middle of Summer can often be detrimental as the cosmos has less time to germinate, and has to contend with particularly high temperatures as it grows and it the flowering period may be late enough in the year that there could be a threat of frost which damages the flowers.

Planting cosmos too early can also risk frost damage from a late frost in the very early Spring which can prevent flowers.

To ensure your cosmos are safe from the risk of frost in the early Spring, it is a good idea to sow the seeds indoors in a greenhouse to protect them whilst they are still tender and give the seedlings time to grow in the early Spring so they can flower as early as possible and for a long time in the Summer.

SHORT DAY FLOWERING - COSMOS WANT TO FLOWER WHEN DAYS ARE SHORTER THAN NIGHTS

Cosmos can often flower best in late Summer or Autumn when as they tend to flower best when the day length is less the 12 hours (short day length plants).

Whilst full sun is beneficial for flowering if cosmos are in bright light for longer then 12 hours then this can impact flowering as the require a period of darkness.

This is due to the cosmos being adapted to sense seasonal change by the pattern of changes in day length so that the plant knows when to flower.

In the northern hemisphere the longest day is on the 21st of June, so cosmos start to develop flowers after this date as the days grow shorter.

If you have a source of light at night that may light up around your cosmos (and other short day plants) then this can reduce flowering even if it is just for a few minutes.

Think of artificial sources of light such as street light or security light that are bright after dark as cosmos require 12 hours of consistent darkness to flower.

In Northerly latitudes the day length tends to be longer which causes the cosmos to flower later in the Summer and perhaps into the Fall.

If you can successfully block out light sources (with horticultural fleece or something similar) so that the day length and hours of light is less then 12 hours then this can help to promote flowers at any time during the Spring or Summer or you can wait until late Summer or Fall for flowering.

CLAY SOIL CAN PREVENT FLOWERING

Clay soil (particularly heavy clay) is not well suited for growing cosmos as it is rich in nutrients (which promotes foliage at the expense of flowers) and does not drain very well and cosmos prefers well draining sandy soil.

If the soil is consistently damp then you cosmos may not necessarily flower.