Cosmos
Cosmos bipinnatus
An ornamental plant, sown February to May.
In September: deadhead the cosmos.
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Cosmos, month by month
Bar: the usual months. Sprout: this month.
| Sowing, planting or job | Sep | Oct | Nov | Dec | 2027Jan | Feb | Mar | Apr | May | Jun | Jul | Aug |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sow under cover. | none | none | none | none | none | usual | usual | usual | none | none | none | none |
| Sow outdoors. | none | none | none | none | none | none | usual | usual | usual | none | none | none |
| Plant out. | none | none | none | none | none | none | none | usual | usual | usual | none | none |
| Pinch out the tips of the cosmos. | none | none | none | none | none | none | none | none | none | usual | none | none |
| Deadhead the cosmos. | usual | usual | none | none | none | none | none | none | none | none | none | none |
What to do, and when
The usual months for a UK garden. Your own plan gives the week.
Sowing and planting
Sow under cover February to April, 5mm deep. Moderate sources: Sarah Raven, Mr Fothergill’s and Suttons.
Sow outdoors March to May, 1.5cm deep, 30cm apart, rows 15 to 20cm apart. Moderate sources: Sarah Raven, Mr Fothergill’s, Suttons and Gardeners’ World.
Plant out April to June, 30cm apart. Moderate sources: Sarah Raven, Mr Fothergill’s and Gardeners’ World.
Pinch out the tips of the cosmos
Once seedlings have 2 to 3 pairs of leaves, pinch out the tips for bushier plants and more flowers. From Gardeners’ World.
Usually June. Moderate source: Sarah Raven.
Deadhead the cosmos
Usually September to October. Moderate source: Sarah Raven.
What the source words mean
Moderate: another trusted UK source, or the RHS on its group.
Every line above names the page it comes from. Where we found no good source for a job, we left it out. Where the name “Cosmos” comes from.