When to sow sweet williams in Mexico City

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 Mexico City.

Mexico City sits in zone 9b, which is milder than this crop wants, and a winter that never really arrives is its own problem. The dates below still describe the right time of year; the open question is survival rather than timing.

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 Mexico City 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.

See every crop timed for Mexico City →