Growing cosmos from seed. In this article, we will learn step by step how to grow annual cosmea from seed (Cosmos bipinnatus).
Flowering continuously from midsummer until autumn, this is one of the best annuals. The flowers are good for cutting and come in shades of white to pink to purple, with yellow centers. Deadhead spent flowers regularly to ensure a display until the first frosts.
They can grow large, almost shrubby, although in containers they may remain compact. Should be pruned from early stage to keep bushy.
The light green feathery foliage is also very attractive. This plant is also good for filling gaps in borders.
Don’t plant in too much rich soil, otherwise they will produce lot of foliage but no flowers.
Although many annuals can be sown directly in the garden, sowing early seeding in a sheltered location gives the plants an advance in growth and a more assured germination that generally produces better results.
Cosmos seeds are better sown in trays and kept at good temperature in a greenhouse, cold frame or even inside in a sunny window sill.
You can buy Cosmos bipinnatus seeds in garden centers, in supermarkets or online. Check the package to see if the seeds are within expiration date and if it is sealed and in good condition. If you need to store seeds for some time, do so in a cool, dry place. A refrigerator is perfect for it.
Cosmea seeds are small but easily handled to sow in a tray.
When to sow
Cosmos can be sown from late winter to mid spring. You can start them earlier in a sheltered place. Keep in mind they will need to be protected until the last frost has passed.
How to sow
Fill the tray with good quality seed compost adding some grit for good drainage. Leave some space below the pot edge. Lightly press the soil to make it firmer.
Distribute the seeds in the tray.
Do not sow too much tighter. This was a mistake I did, I sown to much seeds and you will see the result later in this post .
See how close they are… cosmos germination rate is very high…
Then lightly cover the seeds with more soil. Water the tray with a fine-grained watering can or dip the tray in a bucket of water so it is absorbed from bottom-up.
You can cover the seed tray and keep it protected to improve germination. A temperature of 20 to 23ºC is ideal for the germination to occur.
The seeds had germinate easily…
How to plant
6 days after sowing, there are already seedling emerging.
They grow very fast.
When the seeds have already developed some leaves, it is time to plant them individually. In the picture below, the seedlings are ready to be replanted individually and allowed to grow more before plant in final place. One month passed between sowing and the picture below.
Look how tight and leggy they are. one third of the seeds would be perfectly enough.
Lift the seedlings and plant in small pots.
Allow them to grow and develop. They are fast growers. Prune the top to encourage lateral shoots that will result in bushy plants.
Finally, when they are robust, plant them in the final position. Keep watered in the first weeks until established and dead head to keep the plants flowering.
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