Growing cosmos: planting, sowing & care
With its delicate and colourful flowers, the summer flower cosmos brightens up the garden or balcony. Find out what to bear in mind when planting and caring for the cosmos.
In summer, the cosmos (Cosmos) delight insects with their long flowering period and abundance of pollen and nectar. Their colourful flowers in shades of white, pink and red are real eye-catchers and beautiful to look at. Although most cosmos species and varieties are annuals, they are extremely easy to care for. Keep reading to learn how to plant and sow cosmos as well as its growing requirements.
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Planting cosmos
From July to October, you can admire the splendour of the cosmos. Many insects buzz around the colourful flowers in summer. In order for the summer flower to thrive, a few things need to be taken into account.
The right location for cosmos
The cosmos is a true sun worshipper and prefers a full sun and warm location where the sun shines at least half the day. In a moderately nutritious, humus-rich and well-drained soil, the summer flower can thrive ideally. The cosmos also feels at home in a pot. For pot planting, for example, our Plantura Organic Flower Compost is ideal. It provides the cosmos with the ideal nutrient supply and ensures vigorous root growth and the formation of countless flowers. In addition, the soil is peat-free and thus environmentally friendly in production.
- Perfect for all flowering plants in garden beds & pots
- For beautiful blossoms & healthy plant growth
- Peat-free & organic soil: CO2-saving composition
Note that cosmos does not tolerate water logging at all and prefers a dry to fresh soil. Therefore, it must be well loosened and, if necessary, mixed with sand or gravel to ensure good water drainage. If the cosmos is cultivated in a pot, a drainage layer, for example of expanded clay, should also be laid at the bottom of the pot.
Sowing cosmos
Cosmos is a frost-sensitive plant and should therefore only be sown in late spring. However the cosmos can be grown on the windowsill from March. Plants started indoors have the advantage that they are less susceptible to slugs and may flower earlier.
Sowing cosmos:
- Sowing in the open from May after the last chance of frost
- Moisten the seedbed a little
- Scatter seeds on the bed: leave about 5 – 8cm space between the individual seeds
- Rake in shallowly with a seed depth of about 0.5cm
- Cover minimally with soil and press down lightly
- Ideal germination temperature: approximately 20 °C
- Germination period: 2 – 3 weeks
Growing cosmos indoors:
- Possible from March
- Allow about 2cm of space between the seeds
- Note a seed depth of about 0.5cm
- Sow on nutrient-poor substrate (e.g. Plantura Organic Herb & Seedling Compost)
- Moisten and cover with a plastic bag
- Ideal germination temperature: approximately 20 °C
- Germination period: 2 – 3 weeks
- After germination, place in a cool location at 17 – 18 °C
- When young plants are 8 – 10cm tall, prick out
- Only plant out after the last signs of frost
- Perfect for herbs as well as sowing, propagating & transplanting
- For aromatic herbs & healthy seedlings with strong roots
- Peat-free & organic soil: CO2-saving composition
Tip: as the cosmos is a short-day plant, it needs a day length of about 8 hours for flower production. Therefore, they should not be sown indoors in a room with long hours of daylight.
Instructions: planting cosmos
The splendidly blooming summer flower is quite undemanding and easy to care for. To ensure that it bears many flowers, all that needs to be done is to pay attention to the right location and time of planting.
- Location: full sun
- Soil: low in nutrients, loose, dry to fresh
- Plant out from May after the last signs of frost
- Distance between plants: 30 – 40cm or 3 – 9 plants per m2
- Fill unfertilised substrate to below the first leaves
- Lightly press down and water well
Combining cosmos: dahlias (Dahlia), zinnia (Zinnia) and cosmos (Cosmos) go extremely well together in cottage gardens. Other flowers that go well with cosmos are: calendula (Calendula), aster (Aster), larkspur (Delphinium), phlox (Phlox) or marigold (Tagetes). By the way, cosmos comes into their own in small groups of about three to five plants.
Caring for cosmos
Once you have found a suitable location for the cosmos, it is not particularly demanding in terms of care and produces many colourful flowers without much effort.
Tip: cosmos is very tolerant. Nevertheless, frost damage can occur if they are exposed to temperatures below 15 °C. Common pests are aphids and slugs, mildew can often be seen on the leaves.
Watering and fertilising
In a pot or balcony box, the cosmos naturally needs a little water from time to time. However, the plant can cope with short dry periods without any problems. However, it does not tolerate waterlogging. In a good quality soil, the cosmos does not need fertilisation. On the contrary, if you do not fertilise it, it blooms all the more profusely during the flowering period.
Cutting cosmos
In a flower vase on the dining table, the cosmos is a real eye-catcher. If you want to use it as a cut flower, it is advisable to cut it in the morning on a dry day. This will keep the flowers fresh in the vase for between 5 and 7 days.
Pruning makes sense if you prefer a particularly bushy growth of the plant. The cosmos should be cut back regularly to about one third. The perennial chocolate cosmos can be cut back before the onset of winter and placed in a room where it can overwinter. This will allow numerous flowers to form again the following spring. To ensure a constant rebloom, it is advisable to cut out the wilted flowers regularly.
My cosmos is not flowering: what should I do?
Although the cosmos is very undemanding, it sometimes fails to produce flowers. There can be several reasons for this:
- Nutrient supply: care must be taken that the cosmos grow in a nutrient-poor substrate.
- Too frequent watering – waterlogging: cosmos prefer dry soil.
- If the soil is moderately fertile and sufficiently permeable, fertilising with a flower fertiliser can be useful.
- Short-day plant: sowing too late or sowing indoors in an illuminated room hinders the flower induction of the cosmos and therefore prevents flower formation. To flower, the plants need a short period of light and a long period of darkness.
Billy buttons (Craspedia) also produce beautiful, yellow round flowerheads that can be seen all summer long in the right location.
