Cosmos, a traditional cottage garden annual of the daisy family, is one of nature’s true delights, producing a vast range of large coloured flowers with both single and double flowered varieties available. Each elegant plant displays long slender stems with beautifully graceful, almost fern-like leaves, making them ideal as both cut flower and as border plants.
On top of that they will flower profusely throughout the summer months and right up until the first frosts. They are also very easy to grow in pots, containers or in beds and borders in the garden. Cosmos seeds can be sown directly into the soil or started off early under glass or even on a warm windowsill.
Variety: Cosmos 'Sonata' Mixed
No. of Seeds: 50
Germination Temp: 15 - 18C
Ideal Plant Spacing: For this variety plant spacing is 50cm minimum, or 3 in a large container.
Sow Seeds from: Late Mar - Early June
How to Successfully Grow Cosmos from Seed.
Cosmos are grown from large seeds, making them easy to sow. They germinate quickly and from then on - never stop. Whilst cosmos seeds can be directly seeded into your garden, an early, indoor start, translates into an earlier, so we recommend starting indoors. Sow seeds on a good quality compost straight into pots and cover lightly with compost or vermiculite.
Germination of seeds is usually around 5 - 7 days. Do not place the seedlings outside until after the last frost date your area as cosmos plants are susceptible to frost.
Growing cosmos from seed
Seeds can be sown directly outdoors into well-drained soil after all danger of frosts have passed or alternatively, and for a quicker start, they can be sown under cover. If you decide to get your plants started early, then you can either sow the seeds into modular trays or individually into 7cm pots from March. The seeds are quite large making them very easy to handle. Use a quality seed compost and cover the seed with 3mm of compost or vermiculite and then firm the surface. Water with a watering can and rose attachment and then leave to germinate. Do not allow the pots or trays to dry out.
Harden off and then plant out into their permanent outdoor positions during May or transplant into large pots or containers and then move to a sunny position. Some Cosmos varieties can grow to well over 120cm high so it is recommended to select varieties in the 50cm to 70cm range for most situations. The dwarf variety, Cosmos Sonata, is especially recommended for growing in pots and containers.
You can sow seed directly into beds and borders during May, allowing 50cm between plants. Cosmos will grow in virtually any type of soil and do not need any special treatment or feeding. However, soil that has been previously prepared with the addition of organic matter, will likely produce the most healthy and prolific plants.
Cosmos plants need little attention and will continue to flower until the first frosts but to encourage the growth of new flowers it is advisable to dead-head plants regularly. When dead-heading, remove the stem of the plant also, right down to the first leaf below the flower.
Keep plants well watered during dry spells although they are known to tolerate dry conditions for short periods. Taller plants, usually those above 60cm, may need some support in order to keep them in an upright and tidy condition.
Pests and diseases
Cosmos are rarely affected by pests and diseases but powdery mildew can sometimes affect plants that are grown in shade or if planted too close. Aphids can occasionally be a problem along with thrips. However, both these pests can be easily removed with a jet of water or in severe cases, spray with a proprietary insecticide.