Cosmos
Resist the urge to feed this genus — unlike most summer bedding, Cosmos flowers best in lean soil, and rich ground or regular feeding trades flowers for leafy growth.
Care
Reasonably drought-tolerant once established; overwatering or overly rich soil leads to lush leaves and few flowers.
Free-draining soil of low to moderate fertility — this genus actually flowers best in poorer soil, unlike most bedding plants.
Pinch out the growing tip of young plants to encourage bushier, more floriferous growth. Deadhead spent flowers regularly to prolong flowering right through to the first frost.
Don't feed — this is the classic case where feeding backfires. On rich soil or with fertiliser, cosmos makes a huge ferny plant with almost no flowers; on poor dry ground it flowers until the frosts.
From seed, sown under cover in early spring and planted out after the last frost. It germinates in days, grows fast, and one packet fills a border — there is no reason to bother with cuttings.
Month by month
Months change with the climate: in southern Italy tomatoes go out two months earlier than in England.
- MayPinch out young plants once a few sets of leaves have formed, to encourage bushiness. how ›
- JulyDeadhead spent flowers regularly to keep the display going. how ›
- SeptemberTallest cultivars may need staking or twiggy support, as they carry a lot of flower for their stem width. how ›
Months based on climate: UK. Your choice stays on this device.
- MayPinch out young plants once a few sets of leaves have formed, to encourage bushiness. how ›
- JulyDeadhead spent flowers regularly to keep the display going. how ›
- SeptemberTallest cultivars may need staking or twiggy support, as they carry a lot of flower for their stem width. how ›
Months based on climate: Northern Italy. Your choice stays on this device.
- AprilPinch out young plants once a few sets of leaves have formed, to encourage bushiness. how ›
- JulyDeadhead spent flowers regularly to keep the display going. how ›
- SeptemberTallest cultivars may need staking or twiggy support, as they carry a lot of flower for their stem width. how ›
Months based on climate: Central Italy. Your choice stays on this device.
- AprilPinch out young plants once a few sets of leaves have formed, to encourage bushiness. how ›
- JulyDeadhead spent flowers regularly to keep the display going. how ›
- OctoberTallest cultivars may need staking or twiggy support, as they carry a lot of flower for their stem width. how ›
Months based on climate: Southern Italy and islands. Your choice stays on this device.
Common problems
How to spot it. Vigorous green growth with a disappointing amount of flowering.
What to do. Usually from soil that's too rich or fertile — avoid feeding; this genus prefers to be grown lean.
How to spot it. Tall plants leaning or collapsing, especially after rain or wind.
What to do. Stake or support tall cultivars, or choose a more compact variety next time.
How to spot it. White coating on leaves as the season cools.
What to do. Usually cosmetic this late in the year; remove badly affected leaves if it bothers you.
Popular varieties
Questions
Cosmos: is it hardy?
H3: Half hardy. It survives down to −5 °C.
Can it grow in a pot?
Compact cultivars do well in a large pot; tall types are better in the ground or a big container with support.
Cosmos: when do you prune it?
Pinch out the growing tip of young plants to encourage bushier, more floriferous growth.
Cosmos: when does it flower?
In the climate of UK it flowers in June–October.
When do you feed it?
Don't feed — this is the classic case where feeding backfires. On rich soil or with fertiliser, cosmos makes a huge ferny plant with almost no flowers; on poor dry ground it flowers until the frosts.