Cosmos is a half-hardy annual, which means it loves warmth but cannot tolerate frost. In the UK, this means we either sow indoors from March onwards and plant out after the last frosts, or we sow directly outside from mid-May once the soil has warmed up. Both approaches work well — the choice largely comes down to how early you want flowers and how much indoor growing space you have.

Cosmos seeds are large enough to handle easily and germinate with impressive enthusiasm in a little warmth.

Step by step:

1. Fill your containers. Use a good peat-free seed compost in small modules or 7–9cm pots. Cosmos doesn't need rich compost at this stage — seed compost or a general multi-purpose mix is ideal. Water before sowing so the compost is evenly moist.

2. Sow one or two seeds per module. Cosmos seeds are slender and elongated — easy to handle individually. Push each seed approximately 1cm deep and cover lightly with compost or a little vermiculite.

3. Place in a warm spot. Cosmos germinates best at around 18–21°C. A warm windowsill, propagator or airing cupboard (check daily if using a dark spot) all work well. Germination is usually quick — five to ten days in warmth.

4. Move to bright light immediately after germination. As soon as seedlings emerge, move them to the brightest spot available. Cosmos seedlings stretch quickly towards light — a south-facing windowsill is ideal. Turning pots daily helps prevent them leaning to one side.

5. Thin or pot on. If two seeds germinated in the same module, snip the weaker one at soil level rather than pulling it out. Once seedlings have two or three sets of true leaves, pot on into 9cm pots if they need more root space before planting out.

6. Harden off before planting out. From late April or May, start bringing cosmos outside for increasing periods each day over one to two weeks before leaving them out permanently. Don't rush this stage — a cold shock can set plants back significantly.

7. Plant out after the last frosts. In most of the UK this means from mid-May onwards, though in northern areas or exposed gardens, early June is safer. Space plants around 30–45cm apart in their final position in full sun.

Like sweet peas, cosmos responds beautifully to being pinched out — and it's a step that makes a real difference to the quality and quantity of your display. Unpinched cosmos tends to produce a single tall stem with flowers at the top. Pinched cosmos branches freely, producing a much bushier plant with far more flowers over a longer period.

A simple pinch at the right moment transforms a single-stemmed seedling into a bushy, floriferous plant.

When to pinch out: When seedlings are around 20–25cm tall and have several pairs of leaves, pinch or snip out the very tip of the main stem just above a pair of leaves. This is best done before planting out, though it can also be done shortly after.

What to expect: Within a week or two, you'll see side shoots developing from the leaf joints below the pinch point. Each of these will become a flowering stem — so instead of one or two flowers, you'll have five, six or more. The wait is absolutely worth it.

Once cosmos is in the ground and established, it is wonderfully undemanding. In fact, one of the most important things to understand about cosmos is that it actually performs better in poorer conditions — rich, fertile soil pushes it into lush leafy growth at the expense of flowers. The lean, sunny border is where cosmos truly thrives.

Cosmos fills a border with airy, romantic charm — and asks remarkably little in return.

Cosmos is generally one of the most trouble-free flowers in the cottage garden — but here are the issues worth knowing about, and how to deal with them if they arise.

Indoor-sown cosmos started in March or April will typically begin flowering from late June or early July. Plants sown in May — whether indoors or directly outside — will usually flower from late July or August. Once flowering begins, cosmos is extraordinarily generous, producing a continuous succession of blooms right through until the first frosts of autumn in October or even November in a mild year.

This makes cosmos one of the longest-flowering plants in the cottage garden calendar — a single sowing can give you four or even five months of continuous colour and cutting material.

Once cosmos starts flowering, it rarely stops — right through until the first frosts arrive.

Cosmos is one of the finest and most generous cut flowers a cottage garden can produce. The stems are long, the flowers are beautiful, and the more you cut, the more the plant produces — making it an ideal choice for anyone who loves filling the house with fresh flowers through summer and into autumn.

How to cut for the vase

Cut cosmos early in the morning when stems are well hydrated. Choose stems where the flower is fully open or just about to open — buds cut too early will not open well in the vase. Cut right back to where the stem meets a side shoot or leaf joint, using sharp scissors or snips. Place immediately into deep, cool water.

Cosmos is not the longest-lasting cut flower — expect around five to seven days in a vase — but what it lacks in longevity it more than makes up for in abundance. Because the plant produces so prolifically, you can cut freely and often without any guilt whatsoever.

Is cosmos good for drying?

Cosmos is not typically grown as a dried flower — the petals do not hold their structure or colour well when dried, unlike larkspur or statice. It is very much a fresh flower, best enjoyed in a vase or left in the garden for pollinators. For drying, allow seed heads to ripen fully at the end of the season — these have a quiet, architectural beauty of their own and can also be collected for sowing next year.