When to sow sweet williams in Beijing

Why these dates

Sow in early summer, six weeks after the last frost, in a seedbed. Move the plants to their final position in autumn at 25cm spacing. They flower the following June for a solid six weeks; cutting the stems long encourages more, and a hard cut back afterwards sometimes buys a third year.

Hardy to about -20C as an overwintering plant and needs the cold to flower. Wants sharp drainage and a neutral to alkaline soil; it is short-lived on acid clay.

Seed packets and extension guides express timing as weeks either side of the last spring frost, because that is the only reference point that travels. Sweet williams are timed with planting out 20 weeks after it, and this page simply resolves those offsets against the frost date computed for Beijing.

Hardiness is not the obstacle here. Beijing is zone 7a, comfortably inside the range this crop is rated for, so an established plant should come through an average winter without protection.

This is a two-season crop, so the dates above describe a sowing in one year and a flowering in the next. The plant spends the winter in the ground as a small rosette, which is why the frost-free season in Beijing does not limit it the way it would limit a tomato: it is not trying to finish before the cold arrives, it is trying to be well enough rooted to sit through it. Sowing too late is the real risk, because a plant that goes into winter undersized often fails to flower at all the following year.

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