How to Grow Cosmos
'Cupcakes Blush' from Seed
Pale pink cosmos with petals fused into a shallow cup, on tall plants that flower from midsummer until the frost. The more you pick, the more you get.
'Cupcakes Blush' is a cosmos with a difference. Instead of opening flat, the petals are joined at the edges into a shallow bowl, like a paper cake case. The colour is the palest pink, with some flowers fading almost to white, and the plants grow to a metre or more.
Among the cupped flowers you will also see some ordinary single ones. That is normal for the Cupcakes strain, and most growers enjoy the mix. Grow it like any cosmos: raise it under cover, plant out after the frosts and keep cutting.
Quick Facts at a Glance
Plant Type
Half-hardy annual
Sowing Time
Mar to Jun, under cover
Flowering
July to October
Position
Full sun
Height
1m or more
Difficulty
1 out of 5, very easy
Understanding the Plant
'Cupcakes Blush' is a variety of Cosmos bipinnatus, the common cosmos from Mexico. The Cupcakes strain was selected for petals that fuse together into a cup. Some plants carry mostly cupped flowers, others a mix, and the proportion varies a little with the season.
Cosmos is frost-tender, so it cannot go outside until late May. Once planted, it grows quickly into a tall, airy plant with fine feathery leaves and flowers well into autumn. Bees and hoverflies visit the open flowers constantly.
Poor soil, more flowers
Cosmos grown in rich, well-fed ground puts on huge amounts of leaf and flowers late. An ordinary, unimproved soil in full sun gives shorter, sturdier plants that start flowering sooner.
When & How to Sow
Cosmos seed is long, thin and easy to handle, and it germinates quickly in warmth. Sow under cover from March to June; there is no advantage in sowing too early, as plants cannot go out until the frosts have passed.
Sow in April for the best plants
An April sowing gives plants that are ready to go out at the end of May without sitting in pots for weeks. A June sowing gives a later batch that keeps flowering fresh into October.
Sow in modules, 5mm deep. Sow one or two seeds per cell, cover lightly with compost and keep at around 18 to 20°C. Seedlings usually appear within 7 to 14 days.
Pinch out the tip. When plants have three or four pairs of leaves, nip out the growing tip. This gives bushier plants with many more flowering stems.
Harden off and plant out after frost. Plant out from the end of May, around 45cm apart. In windy gardens, put in a stake or run string supports along the row at planting time.
Growing On Tips
Full sun
Give it the sunniest spot you have, in average soil without extra feeding.
Support tall plants
At a metre or more, plants can blow over in exposed spots. A stake or a row of netting keeps them upright.
Cut constantly
Cosmos flowers harder the more you pick. Cut stems down to a side shoot and remove any seed heads you miss.
In the vase
Cut when flowers are just opening. The cupped shape looks lovely in small jugs and posies.
Watering
Water newly planted cosmos until established. After that, only water in long dry spells.
Pollinators
Bees and hoverflies work the open flowers from July until the frost.
Common Problems & How to Fix Them
| Problem | Likely Cause | What to Do |
|---|---|---|
| Some flowers flat, not cupped | Normal for the Cupcakes strain | A proportion of single flowers is expected. Enjoy the mix, or save seed only from the most cupped plants. |
| Tall plants with few flowers | Soil too rich or overfed | Stop feeding. Next year plant into unimproved ground in full sun. |
| Plants blown over | No support in an exposed spot | Stake plants or run netting along the row when you plant out. |
| Leggy seedlings | Too little light or sown too early | Grow seedlings in the brightest place you have and pinch them out. Sowing in April avoids long waits in pots. |
| Young plants eaten | Slugs and snails | Protect new plantings for the first few weeks. Established cosmos is rarely troubled. |
When to Expect Flowers
Plants sown in April and set out at the end of May usually start flowering in July. Keep cutting and they carry on until the first frost, often into October.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 🌱 Sow under cover | ||||||||||||
| 🪴 Plant out | ||||||||||||
| 🌸 Flowering |
Plant Specifications
Cup-shaped cosmos in the softest pink
Sow under cover in spring, plant out at the end of May and keep cutting. You will have pale pink cups for the house from July until the frost.
Shop Cosmos Cupcakes Blush Seeds →