How to grow cosmos

How to grow Cosmos

Cosmos are easy to grow from seeds, if they are located on a sunny spot. They form a cloud of color that not only looks attractive throughout the summer but also attracts bees, butterflies, and birds to your garden.

Location

For the best flowering, choose a site that gets full sun. Avoid soils that are too rich, they will do best in well-drained poor soils. They will survive winter as seeds and will self-sow, if you leave some seeds.

Sowing

For an early blooming, you can start seeds indoors from March/April. Use a growing medium that is relatively low in nutrients and may also contain a little sand. Plant the seeds and cover them with some soil (0,25 cm). The optimal germination temperature is about 20°C, then the first seedlings appear after 12-21 days. Important: keep moist, but not wet. A water sprayer is best suited for this. When the seedlings are 8-10 cm tall, prick them out. They should only be planted outdoors after the last night frosts.

Cosmos sown outdoors directly in the garden will quickly catch up. Wait until all danger of frost has passed before sowing or transplanting outdoors. Cosmos grow very quickly but can be killed by a late frost, so don`t rush it. The soil should be rather poor and kept evenly moist.
Seed packets usually recommend precise spacing, but you will get a better display if you simply scatter the seeds and let the plants support each other as they grow. You can always thin if you need to, moving the extra plants to another part of the garden.

Care

You should not need to water your cosmos plants at all unless there is a prolonged drought. Where water is limited, these are the last plants that require irrigation. Only the young seedlings need even moisture. Cosmos do not need fertilizer at all. And fertilizing can actually have a negative impact. Too much fertilizer can create strong plants with lots of foliage-but few blooms. For a bushier growth you can cut the plants from a height of 40 cm, but be careful not to remove too many flower shoots.

Flowering

Flowering starts in May and can last until the end of September or, in a sunny spot, until the first frost. The only real maintenance cosmos plants need is deadheading which will prolong the flowering season. The flowers are edible and a great eye-catcher in salads.

Protection against pests and diseases

Cosmos is robust, there are only some pests, like aphids, flea beetles, and thrips. They`re easy to control with a strong spray of water with soap. Powdery mildew may also affect cosmos. Space plants accordingly to ensure good airflow to avoid diseases.